WO2006065774A1

WO2006065774A1 - Inter-facet implant

Info

Publication number: WO2006065774A1
Application number: PCT/US2005/044979
Authority: WO
Inventors: Charles J. Winslow; James F. Zucherman; Ken Y. Hsu; Steven T. Mitchell; Scott A. Yerby; John J. Flynn; Carl Lauryssen
Original assignee: St. Francis Medical Technologies, Inc.
Priority date: 2004-12-13
Filing date: 2005-12-13
Publication date: 2006-06-22
Also published as: EP1824427A1; CA2590049A1; IL182915A0; JP2008522787A; KR20070108151A; AU2005316646A1; AU2005316646B2; EP1824427A4; MX2007006808A

Abstract

Systems and method in accordance with the embodiments of the present invention can include an implant (1900) for positioning within a facet joint for distracting the spine, thereby increasing the area of the canals and openings through which the spinal cord and nerves must pass, and decreasing pressure on the spinal cord and/or nerve roots. The implant (1900) can be inserted laterally or posteriorly.

Description

INTER-FACET IMPLANT

CLAIM OF PRIORITY

This application claims priority to the following applications, which are all incorporated herein by reference:

United States Provisional Application No. 60/635,453 entitled INTER-CERVICAL FACET IMPLANT AND METHOD, by James F. Zucherman et al., filed December 13, 2004 (Attorney Docket No. KLYC-01118US0);

United States Provisional Application No. 60/668,053 entitled INTER-CERVICAL FACET IMPLANT DISTRACTION TOOL, by Scott A. Yerby et al , filed April 4, 2005 (Attorney Docket No. KLYC-01125US0);

United States Provisional Application No. 60/679,363 entitled INTER-CERVICAL FACET IMPLANT WITH IMPLANTATION TOOL, by Charles J. Winslow et al , filed May 10, 2005 (Attorney Docket No. KLYC-01118US7);

United States Provisional Application No. 60/679,361 entitled INTER-CERVICAL FACET IMPLANT WITH IMPLANTATION TOOL, by Charles J. Winslow et al. , filed May 10, 2005; (Attorney Docket No. KLYC-01118US8); United States Provisional Application No. 60/679,377 entitled INTER-CERVICAL FACET

IMPLANT WITH IMPLANTATION TOOL, by Charles J. Winslow et al , filed May 10, 2005 (Attorney Docket No. KLYC-01118US9);

United States Provisional Application No. 60/687,765 entitled INTER-CERVICAL FACET IMPLANT WITH MULTIPLE DIRECTION ARTICULATION JOINT AND METHOD FOR IMPLANTING, by James F. Zucherman et al. , filed June 6, 2005 (KLYC-01118US6);

United States Provisional Application No. 60/717,369 entitled INTER-CERVICAL FACET IMPLANT WITH SURFACE ENHANCEMENTS, by James F. Zucherman et al, filed September 15, 2005; (Attorney Docket No. KLYC-01133USO);

United States Utility Patent Application No. 11/053,399 entitled INTER-CERVICAL FACET IMPLANT AND METHOD, by Charles J. Winslow et al. , filed February 8, 2005 (Attorney Docket No. KLYC-01118US 1);

United States Utility Patent Application No. 11/053,624 entitled INTER-CERVICAL FACET IMPLANT AND METHOD, by Charles J. Winslow et al , filed February 8, 2005 (Attorney Docket No KLYC-011 18US2); United States Utility Patent Application No. 1 1/053,735 entitled INTER-CERVICAL FACET IMPLANT AND METHOD, by Charles J Winslow et al , filed February 8, 2005 (Attorney Docket No. KLYC-Ol 118US3);

United States Utility Patent Application No. 1 1/053,346 entitled INTER-CERVICAL FACET IMPLANT AND METHOD, by Charles J. Winslow et al , filed February 8, 2005 (Attorney Docket No. KLYC-01122US0);

United States Utility Patent Application No. 11/093,557 entitled INTER-CERVICAL FACET IMPLANT WITH LOCKING SCREW AND METHOD, by Charles J. Winslow et al , filed March 30, 2005 (KLYC-01118US5); and United States Utility Patent Application No. 11/093,689 entitled INTER-CERVICAL FACET

IMPLANT AND METHOD FOR PRESERVING THE TISSUES SURROUNDING THE FACET JOINT, by Carl Lauryssen et al, filed March 30, 2005 (KLYC-01124US0).

TECHNICAL FIELD This invention relates to interspinous process implants.

BACKGROUND OF THE INVENTION

The spinal column is a bio-mechanical structure composed primarily of ligaments, muscles, vertebrae and intervertebral disks. The bio-mechanical functions of the spine include: (1) support of the body, which involves the transfer of the weight and the bending movements of the head, trunk and arms to the pelvis and legs, (2) complex physiological motion between these parts, and (3) protection of the spinal cord and the nerve roots.

As the present society ages, it is anticipated that there will be an increase in adverse spinal conditions which are characteristic of older people. By way of example only, with aging comes an increase in spinal stenosis (including, but not limited to, central canal and lateral stenosis), and facet arthropathy.

Spinal stenosis results in a reduction foraminal area (i.e., the available space for the passage of nerves and blood vessels) which compresses the cervical nerve roots and causes radicular pain. Humpreys, S.C. et al.,

Flexion and traction effect on C5-C6 foraminal space, Arch. Phys. Med. Rehabil., vol. 79 at 1105 (Sept.

1998). Another symptom of spinal stenosis is myelopathy, which results in neck pain and muscle weakness. Id. Extension and ipsilateral rotation of the neck further reduces the foraminal area and contributes to pain, nerve root compression, and neural injury. Id.; Yoo, J.U. et al., Effect of cervical spine motion on the neuroforaminal dimensions of human cervical spine, Spine, vol. 17 at 1131 (Nov. 10, 1992).

In contrast, neck flexion increases the foraminal area. Humpreys, S.C. et al., supra, at 1105.

In particular, cervical radiculopathy secondary to disc herniation and cervical spondylotic foraminal stenosis typically affects patients in their fourth and fifth decade, and has an annual incidence rate of 83.2 per 100,000 people (based on 1994 information). Cervical radiculopathy is typically treated surgically with either an anteπor cervical discectomy and fusion ("ACDF") or posterior laminoforaminotomy ("PLD"), with or without facetectomy. ACDF is the most commonly performed surgical procedure for cervical radiculopathy, as it has been shown to increase significantly the foramina dimensions when compared to a PLF.

It is desirable to eliminate the need for major surgery for all individuals, and in particular, for the elderly. Accordingly, a need exists to develop spme implants that alleviate pain caused by spinal stenosis and other such conditions caused by damage to, or degeneration of, the cervical spine. The present invention addresses this need with implants and methods for implanting an apparatus into at least one facet joint of the cervical spine to distract the cervical spme while preferably preserving mobility and normal lordotic curvature.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a lateral view of two adjacent cervical vertebrae and spinous processes, highlighting the cervical facet joint.

FIG. 2 depicts a lateral view of the cervical spine with spinal stenosis

FIG.3 A depicts correction of cervical stenosis or other ailment with a wedge-shaped embodiment of the implant of the invention positioned in the cervical facet joint. FIG. 3B depicts correction of cervical kyphosis or loss of lordosis with a wedge-shaped embodiment of the invention with the wedge positioned in the opposite direction as that depicted in FIG. 3A.

FIG. 4 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention including a screw fixation device for attaching to a single vertebra. FIG. 5 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising screw fixation of two implants, one implant fixed to each of two adjacent vertebrae.

FIG. 6 shows cervical spine kyphosis, or loss of lordosis.

FIG. 7 shows correction of cervical kyphosis, or loss of lordosis, with a further embodiment of the implant of the invention comprising two facet implants with screw fixation.

FIG. 8 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising a facet implant and a keel.

FIG. 9 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising facet implant, a keel, and screw fixation. FIG. 10 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, compπsing a facet implant with teeth.

FIG. 11 depicts correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, compπsing a facet implant with teeth and screw fixation. FIG. 12 depicts correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising two facet implants having bony ingrowth surfaces.

FIG. 13 depicts correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, compπsing two facet implants having bony ingrowth surfaces and posterior alignment guide. FIG. 14 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, compπsing two facet implants with increased facet joint contact surfaces.

FIG. 15 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising two facet implants having bony ingrowth surfaces and screw fixation.

FIG. 16 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising two facet implants with articular inner surfaces.

FIG. 17 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising a facet joint implant with a roller.

FIG. 18 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising a facet joint implant with a plurality of rollers. FIG. 19 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising two facet joint implants, screw fixation, and elastic restraint.

FIG. 20 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, compπsing two facet joint implants, screw fixation, and spring restraint.

FIG. 21 shows correction of cervical stenosis or other ailment with a further embodiment of the implant of the invention, comprising two facet joint implants, screw fixation, and magnetic restraint.

FIG. 22 A shows a perspective view of a further embodiment of implant of the invention.

FIG. 22B shows a perspective exploded view of the embodiment of the invention shown in FIG. 22A.

FIG. 23 A depicts a posterior view of the embodiment of the implant of the invention shown in FIG. 22A.

FIG. 23B shows a posterior view of a locking plate of the embodiment of the implant of the invention shown in FIG. 22A.

FIG. 24 A depicts a lateral side view of the embodiment of the implant of the invention shown in FIG. 22A FIG. 24B shows a lateral side view of the keel of the locking plate of the embodiment of the implant of the invention shown in FIG. 22 A.

FIG. 25A shows a perspective view of a further embodiment of the implant of the invention.

FIG. 25B shows a side view of the embodiment of the implant of the invention in FIG. 25A, having a curved, uniformly-thick artificial facet joint spacer or inter-facet spacer including a tapered end

FIG. 26A shows a perspective view of a further embodiment of the implant of the invention having a locking cam in a first position.

FIG. 26B shows a posterior view of the embodiment of the implant of the invention depicted in FIG. 26A. FIG. 27A depicts a side view of the embodiment of the implant of the invention shown in FIGS.

26A and 26B, implanted in the cervical spine

FIG. 27B shows a posterior perspective view of the embodiment of the implant of the invention shown in FIGs. 26A, 26B, and FIG. 27A.

FIG. 28A depicts a posterior perspective view of a further embodiment of the implant of the invention.

FIG. 28B depicts a side view of the embodiment of the implant of the invention shown in FIG. 28A.

FIG. 29A depicts a side view of an embodiment of a sizing tool of the invention

FIG. 29B depicts a top view of an embodiment of the sizing tool of the invention depicted in FIG. 29A.

FIG. 29C depicts a perspective view of an embodiment of the sizing tool of the invention depicted in FIGs. 29A and 29B.

FIG 29D depicts a side view of the head of the sizing tool of the invention depicted in FIG. 29A.

FIG. 29E depicts a cross-sectional view of the head of the sizing tool of the invention depicted in FIGS. 29A-29C.

FIG. 30 is a flow diagram of an embodiment of a method of the invention.

FIG. 31 A is posterior view of a further embodiment of the implant of the invention

FIG. 31B is a side view of an embodiment of a locking screw of the implant of the invention depicted in FIG. 3 IA. FIG. 32 is a posterior view of a further embodiment of the implant of the invention

FIGs. 33 A and 33B depict initial and final insertion positions of the embodiment of the invention depicted in FIG 32.

FIGs. 34A and 34B illustrate a top and bottom plan view of an alternative embodiment of an mter-cervical facet implant in accordance with the present invention.

FIG. 35 is a partially exploded perspective view of the implant of FIGs. 34A and 34B.

FIGs. 36A and 36B illustrate side views of the implant of FIGs. 34A and 34B illustrating a general range of motion of the implant. FIG. 37 is a side view of still another embodiment of an implant in accordance with the present invention

FIG. 38 is a flow diagram of an embodiment of a method in accordance with the present invention

FIG. 39 A is a posterior view of a further embodiment of the implant of the invention.

FIG. 39B is a side view of a further embodiment of the implant of the invention. FIG. 4OA is a perspective view of an embodiment of the implantation tool of the invention.

FIG. 4OB is a perspective view of the engagement head of the implantation tool of the invention.

FIG. 41 A shows a perspective view of a further embodiment of the implant of the invention having a locking cam in a first position. FIG. 41B shows a perspective view of a further embodiment of the implant of the invention having a locking cam in a second position.

FIG. 42A is a side view of still another embodiment of an implant in accordance with the present invention.

FIG. 42B is a top view of the implant of FIG. 42A. FIG. 42C is a bottom view of the implant of FIG. 42 A.

FIG. 42D-F are side views of the implant of FIG. 42A illustrating the various arrangements of a bone screw associated the implant.

FIG. 42G is an end view of the implant of FIG. 42F illustrating the arrangement of the bone screw associated the implant from an alternative viewing angle. FIG. 43 is a side view of still another embodiment of an implant in accordance with the present invention.

FIG. 44 illustrates a side view of a distraction tool in accordance with one embodiment of the present invention.

FIG. 45 illustrates a side view of the distraction tool in accordance with one embodiment of the present invention.

FIG. 46 A illustrates a perspective view of a distraction head of the distraction tool in accordance with one embodiment of the present invention.

FIG. 46B illustrates a perspective view of the distraction head of the distraction tool in accordance with one embodiment of the present invention. FIG. 47 A illustrates a side view of a curved distraction head of the distraction tool in accordance with one embodiment of the present invention.

FIG. 47B illustrates a side view of the curved distraction head of the distraction tool in accordance with one embodiment of the present invention FIG. 48A illustrates a perspective view of a distraction tool in accordance with one embodiment of the present invention.

FIG. 48B illustrates a top view of the distraction tool in accordance with one embodiment of the present invention

FIGs. 49A-49C illustrate one distraction process using the distraction tool of the present invention.

FIG. 49D illustrates a flow chart of one implantation method in accordance with one embodiment of the present invention.

FIG. 5OA illustrates a perspective view of a distraction and insertion tool in accordance with one embodiment of the present invention. FIG. 5OB illustrates a top view of the distraction and insertion tool shown in FIG. 5OA in accordance with one embodiment of the present invention.

FIG. 51 illustrates a perspective view of a distraction tool with sizing mechanism in accordance with one embodiment of the present invention.

Detailed Description

Embodiments of the present invention provide for a minimally invasive surgical implantation method and apparatus for cervical spine implants that preserves the physiology of the spine. In particular, embodiments provide for distracting the cervical spine to increase the foraminal dimension in extension and neutral positions. Such implants, when implanted in the cervical facet joints, distract, or increase the space between, the vertebrae to increase the foraminal area or dimension, and reduce pressure on the nerves and blood vessels of the cervical spine.

The facet joints in the spine are formed between two vertebrae as follows. Each vertebra has four posterior articulating surfaces: two superior facets and two inferior facets, with a supeπor facet from a lower vertebra and an inferior facet of an upper vertebra forming a facet joint on each lateral side of the spine. In the cervical spine, the upward inclination of the superior articular surfaces of the facet joints allows for considerable flexion and extension, as well as for lateral mobility. Each facet joint is covered by a dense, elastic articular capsule, which is attached just beyond the margins of the articular facets The capsule is larger and looser in the cervical spine than in the thoracic and lumbar spine. The inside of the capsule is lined by a synovial membrane which secretes synovial fluid for lubricating the facet joint. The exterior of the joint capsule is surrounded by a capsular ligament. It is this ligament and the joint capsule that must be cut in the embodiments of the method described herein for inserting the artificial facet joint spacer or inter-facet spacer.

In a specific preferred embodiment, an implanted interfacet spacer of 1 5 mm to 2.5 mm in width can result in interfacet distraction that increases foraminal dimension in extension and neutral Other interfacet spacer dimensions also are contemplated by the invention described herein below. The present embodiments also preserve mobility of the facet joints.

Further embodiments of the present invention accommodate the distinct anatomical structures of the spine, minimize further trauma to the spine, and obviate the need for invasive methods of surgical implantation. Embodiments of the present invention also address spinal conditions that are exacerbated by spinal extension.

FIG. 1 shows a simplified diagram of a portion of the cervical spine, focusing on a cervical facet joint 1 formed between two adjacent cervical vertebrae. The spinous processes 3 are located posteriorly and the vertebral bodies 5 are located anteriorly, and a nerve root canal 7 is visible. Each vertebra has four posterior articulating surfaces: two superior facets and two infeπor facets, with a superior facet from a lower vertebra and an infeπor facet of an upper vertebra forming a facet joint on each lateral side of the spme. In the cervical spine, the upward inclination of the superior articular surfaces of the facet joints allows for considerable flexion and extension, as well as for lateral mobility. Each facet joint is covered by a dense, elastic articular capsule, which is attached just beyond the margins of the articular facets. The capsule is large and looser in the cervical spme than in the thoracic and lumbar spine. The inside of the capsule is lined by a synovial membrane which secretes synovial fluid for lubricating the facet joint. The exterior of the joint capsule is surrounded by a capsular ligament. It is this ligament that may be pushed out of the way in the embodiments of the method for inserting the facet joint spacer or inter-facet spacer, described herein. FIG. 2 depicts cervical foraminal stenosis. From the drawing, the nerve root canal 7 is narrowed relative to the nerve root canal 7 depicted in FIG. 1. The spinal canal and/or intervertebral foramina also can be narrowed by stenosis. The narrowing can cause compression of the spinal cord and nerve roots.

FIG. 3A shows a first embodiment 100 of the present invention, which is meant to distract at least one facet joint, in order to increase the dimension of the neural foramen while retaining facet joint mobility. The wedge-shaped embodiment or inter-facet spacer 100 is a wedge-shaped implant that can be positioned in the cervical facet joint 101 to distract the joint and reverse narrowing of the nerve root canal 107. In this embodiment or inter-facet spacer 100, the implant is positioned with the narrow portion of the wedge facing anteriorly. However, it is also within the scope of the present invention to position embodiment or inter-facet spacer 100 (FIG. 3B) with the wide portion of the wedge facing anteriorly, to correct for cervical kyphosis or loss of cervical lordosis.

Referring to FIG.4, the embodiment 200 of the implant has a joint insert or inter-facet spacer 210, also herein referred to as a facet joint spacer or inter-facet spacer, that is positioned in the cervical facet joint 101. The joint insert or inter-facet spacer 210 can be wedge-shaped with the narrow part of the wedge facing anteriorly. Alternatively, the joint insert or inter-facet spacer 210 need not be wedge-shaped but can be of substantially uniform thickness, the thickness determined by an individual patient's need for distraction of the cervical facet joint 201. As with embodiment 100, one objective of this embodiment is facet joint distraction, and joint mobility after implantation. The joint insert or mter-facet spacer 210 is continuous with a posterior sheath 220 bent at an angle from the joint insert or mter-facet spacer 210 to align substantially parallel with the bone. The posteπor sheath can lie against the lamina, preferably against the lateral mass. The posteπor sheath 220 can have a bore 230 which can accept a bone screw 240. Alternatively, the bore 230 can accept any other appropriate and/or equivalent fixation device capable of fixing the embodiment 200 to the spine. The device is thereby affixed to the vertebra, preferably by fixing to the lateral mass. FIG. 5 shows embodiment 300, which is the use of two embodiments 200, each fixed to one of two adjacent cervical vertebrae. As with embodiment 200, the implanted facet joint is distracted andjoint mobility is retained. A joint insert or inter-facet spacer 310 from each of the two implants is inserted and positioned in the cervical facet joint 301. In this embodiment, the joint inserts or inter-facet spacers 310 are substantially flat and parallel to each other and are not wedge-shaped. Alternatively, thejomt inserts or inter-facet spacers 310 can together define a wedge-shaped insert that is appropriate for the patient. The two joint inserts or inter-facet spacers 310 combined can have, by way of example, the shape of the joint insert or mter-facet spacer 210 in FIG.4. Embodiment 300 then can be fixed to the spine with a screw 340 or any other appropriate fixation device, inserted through a bore 330 in the posterior sheath 320. The posterior sheath 320 can be threaded to accept a screw. The screw can be embedded in the lamina, preferably in the lateral mass, where possible.

It is within the scope of the present invention to use and/or modify the implants of the invention to correct cervical spine kyphosis, or loss of lordosis. FIG. 6 depicts a cervical spine lordosis. FIG. 7 demonstrates an embodiment 400 which contemplates positioning two implants to correct for this spinal abnormality while retaining facet joint mobility. Thejoint insert or mter-facet spacer 410 of each implant is shaped so that it is thicker at its anterior portion. Alternatively, the implants can be shaped to be thicker at the posterior ends, for example as depicted in FIG.3 A. The posteπor sheath 420 of each implant is bent at an angle from thejoint insert or inter-facet spacer 410 to be positioned adjacent to the lateral mass and/or lamina, and has a bore 430 to accept a screw 440 or other appropriate and/or equivalent fixation means to fix the embodiment 400 to the spine, preferably to the lateral mass. The placement of two joint inserts or inter-facet spacers 410 in the cervical facet joint 401 distracts the facet joint, which shifts and maintains the vertebrae into a more anatomical position to preserve the physiology of the spine.

FIG. 8 shows a further embodiment 500 of the implant of the invention, wherein the joint insert or inter-facet spacer 510 has a keel 550 on an underside of the joint insert or inter-facet spacer 510. The keel 550 can be made of the same material or materials set forth above. The surfaces of the keel 550 can be roughened in order to promote bone ingrowth to stabilize and fix the implant 500. In other embodiments, the keel 550 can be coated with materials that promote bone growth such as, for example, bone morphogenic protein ("BMP"), or structural mateπals such as hyaluronic acid "HA," or other substances which promote growth of bone relative to and into the keel 550.

The keel 550 can be embedded in the facet bone, to facilitate implant retention. The keel 550 can be placed into a channel in the facet bone. The channel can be pre-cut. Teeth (not shown), preferably positioned posteriorly, also may be formed on the keel 550 for facilitating retention of the implant 500 in the cervical facet joint 501. As noted above, the joint insert or inter-facet spacer 510 can be substantially flat or wedge-shaped, depending upon the type of distraction needed, i.e., whether distraction is also necessary to correct abnormal curvature or lack of curvature in the cervical spine. Because the joint is not fused, mobility is retained, as with the embodiments described above and herein below.

FIG. 9 illustrates that a further embodiment 600 of the implant of the invention can have both screw fixation and a keel 650 for stability and retention of the implant 600. On embodiment 600, the joint insert or mter-facet spacer 610 is continuous with a posterior sheath 620 having a bore hole 630 to accept a screw 640 which passes through the bore 630 and into the bone of the vertebrae, preferably into the lateral mass, or the lamina. The bore 630 can be threaded or not threaded where it is to accept a threaded screw or equivalent device. Alternatively, the bore 630 need not be threaded to accept a non-threaded equivalent device. The keel 650 is connected with the joint insert or mter-facet spacer 610 and embeds in the bone of the cervical facet joint 601 to promote implant retention.

A further alternative embodiment 700 is illustrated in FIG. 10. In this embodiment 700, thejoint insert or inter-facet spacer 710 has on a lower side at least one tooth 760. It should be clear to one of ordinary skill in the art that a plurality of teeth 760 is preferable. The teeth 760 are able to embed in the bone of the cervical facet joint 701 to facilitate retention of the implant 700 in the joint 701. The teeth 760 can face m a direction substantially opposite the direction of insertion, for retention of the implant 700. As above, the joint insert or inter-facet spacer 710 can be wedge-shaped or substantially even in thickness, depending upon the desired distraction. Because the implant distracts and is retained without fusion, facet joint mobility is retained. FIG. 11 depicts a further embodiment 800 of the implant of the invention. In this embodiment 800, the joint insert or inter-facet spacer 810 is continuous with a posteπor sheath 820 having a bore 830 for accepting a fixation device 840, as described above. The fixation device 840 can be a screw which fits into a threaded bore 830; alternatively, the fixation device 830 can be any other compatible and appropriate device. This embodiment 800 further combines at least one tooth 860 on an underside of the joint insert or inter-facet spacer 810 with the posterior sheath 820, bore 830 and fixation device 840 to address fixation of the implant 800 in a cervical facet joint 801. It will be recognized by one of ordinary skill in the art that the implant 800 can have a plurality of teeth 860 on the underside of the joint insert or inter-facet spacer 810. FIG. 12 shows yet another embodiment 900 of an implant of the present invention. In this embodiment 900, the joint inserts or inter-facet spacers 910 of two implants 900 are positioned in a cervical facet joint 901. As descπbed above, the joint inserts or inter-facet spacers 910 can be wedge- shaped as needed to restore anatomical curvature of the cervical spine and to distract, or thejoint inserts or inter-facet spacers 910 can be of substantially uniform thickness. The implants 900 each compnse ajoint insert or inter-facet spacer 910 with an outer surface 970 that interacts with the bone of the cervical facet joint 901. On the upper implant 900, the surface 970 that interacts with the bone is the upper surface 970 and on the lower implant 900, the surface 970 that interacts with the bone is the lower surface 970. Each surface 970 can comprise a bone ingrowth surface 980 to create a porous surface and thereby promote bone ingrowth and fixation. One such treatment can be with plasma spray titanium, and another, with a coating of sintered beads. Alternatively, the implant 900 can have casted porous surfaces 970, where the porous surface is integral to the implant 900. As a further alternative, the surfaces 970 can be roughened in order to promote bone ingrowth into these defined surfaces of the implants 900. In other embodiments, the surfaces 970 can be coated with materials that promote bone growth such as for example bone morphogeny protein ("BMP"), or structural materials such as hyaluronic acid ("HA"), or other substances which promote growth of bone on other external surfaces 970 of the implant 900. These measures facilitate fixation of the implants 900 in the facet joint, but do not result in fusion of the joint, thereby retaining facet joint mobility, while also accomplishing distraction of the joint.

FIG. 13 depicts yet another embodiment 1000 of the implant of the present invention. In this embodiment 1000, the joint inserts or inter-facet spacers 1010 of two implants 1000 are positioned in a cervical facet joint 1001. As described above, thejoint inserts or mter-facet spacers 1010 can be wedge- shaped as needed to restore anatomical curvature of the cervical spine and to distract, or thejoint inserts or inter-facet spacers 1010 can be of substantially uniform thickness. The implants 1000 each comprise a _joint insert or inter-facet spacer 1010 with an outer surface 1070 that interacts with the bone of the cervical facet joint 1001. On the upper implant 1000, the surface 1070 that interacts with the bone is the upper surface and on the lower implant 1000, the surface 1070 that interacts with the bone is the lower surface. As set forth above, each outer surface 1070 can comprise a bone ingrowth surface 1080 to create a porous surface and thereby promote bone ingrowth and fixation, without facet joint fusion and loss of mobility. In one preferred embodiment, the bone ingrowth surface 1080 can be created with plasma spray titanium, and/or with a coating of sintered beads. In an alternative preferred embodiment, the implant 1000 can have casted porous surfaces 1070, where the porous surface is integral to the implant 1000. In a further alternative preferred embodiment, the surfaces 1070 can be roughened in order to promote bone ingrowth into these defined surfaces of the implants 1000. In other preferred embodiments, the surfaces 1070 can be coated with materials that promote bone growth such as for example BMP, or structural materials such as HA, or other substances which promote growth of bone on other external surfaces 1070 of the implant 1000.

The implant 1000 can have a posterior alignment guide 1090. The posterior alignment guides 1090 of each implant 1000 can be continuous with the joint inserts or inter-facet spacers 1010. The posterior alignment guides substantially conform to the bone of the vertebrae when the joint inserts or inter-facet spacers 1010 are inserted into the cervical facet joint 1001. The posterior alignment guides 1090 are used to align the implants 1000 so that the joint inserts or inter-facet spacers 1010 contact each other and not the bones of the cervical facet joint 1001 when the joint inserts or inter-facet spacers 1010 are positioned in the cervical facet joint 1001. FIG. 14 depicts a further embodiment 1100 of the implant of the present invention. In this embodiment 1100, the joint inserts or inter-facet spacers 1110 of two implants 1100 are inserted into the cervical facet joint 1101. Each of the joint inserts or mter-facet spacers 1110 is continuous with a cervical facet joint extender or facet-extending surface 1192. The bone contacting surfaces 1170 of thejoint inserts or inter-facet spacers 1110 are continuous with, and at an angle to, the bone contacting surfaces 1193 of the cervical facet joint extenders 1192, so that the cervical facet joint extenders 1192 conform to the bones of the vertebrae exterior to the cervical facet joint 1101. The conformity of the cervical facet joint extenders 1192 is achieved for example by forming the cervical facet joint extenders 1192 so that when the join inserts 1110 are positioned, the cervical facet joint extenders 1192 curve around the bone outsider the cervical facet joint 1101. The cervical facet joint extenders have a second surface 1184 that is continuous with the joint articular surfaces 1182 of the joint inserts or inter-facet spacers 1110. The second surfaces 1184 extend the implant 1100 posteriorly to expand the joint articular surfaces 1182 and thereby to increase contact and stability of the spine at least in the region of the implants 1100. It is to be understood that such facet joint extenders 1192 can be added to the other embodiments of the invention descπbed and depicted herein.

The embodiment depicted in FIG. 15 shows two implants 1200 positioned in a cervical facet joint

1201, having bony ingrowth surfaces as one preferred method of fixation, and using screws as another preferred method of fixation. In this embodiment, each of two implants 1200 has a joint insert or inter- facet spacer 1210 positioned in a cervical facet joint 1201. As described above, the joint inserts or lnter- facet spacers 1210 can be wedge-shaped as needed to restore anatomical curvature of the cervical spine and to distract, or the joint inserts or inter-facet spacers 1210 can be of substantially uniform thickness. The implants 1200 each comprise a joint insert or inter-facet spacer 1210 with an outer surface 1270 that interacts with the bone of the cervical facet joint 1001. On the upper implant 1200, the surface 1270 that interacts with the bone is the upper surface and on the lower implant 1200, the surface 1270 that interacts with the bone is the lower surface. As set forth above, each outer surface 1270 can comprise a bone ingrowth surface 1280 to create a porous surface and thereby promote bone ingrowth and fixation. In one preferred embodiment, the bone ingrowth surface 1280 can be created with plasma spray titanium, and/or with a coating of sintered beads. In an alternative preferred embodiment, the implant 1200 can have casted porous surfaces 1270, where the porous surface is integral to the implant 1200 In a further alternative embodiment, the surfaces 1270 can be roughened in order to promote bone ingrowth into these defined surfaces of the implants 1200. In other preferred embodiments, the surfaces 1270 can be coated with materials that promote bone growth such as for example BMP, or structural materials such as HA, or other substances which promote growth of bone on other external surfaces 1270 of the implant 1200 Screw fixation or other appropriate fixation also can be used with implants 1200 for fixation in the cervical facet joint 1201. The joint insert or inter-facet spacer 1210 is continuous with a posteπor sheath 1220 bent at an angle from the joint insert or mter-facet spacer 1210 to align substantially parallel with the bone, preferably the lateral mass or lamina The posteπor sheath 1220 can have a bore 1230 which can accept a bone screw 1240, preferably into the lateral mass or lamina. Alternatively, the bore 1230 can accept any other appropriate and/or equivalent fixation means for fixing the embodiment 1200 to the spine.

FIG. 16 depicts a further preferred embodiment of the present invention In this embodiment 1300, two joint inserts or inter-facet spacers 1310 are positioned in the cervical facet joint 1301. Thejomt inserts or mter-facet spacers each have outer surfaces 1370 that interact with the bone of the vertebrae forming the cervical facet joint These outer surfaces 1370 of the embodiment 1300 can be treated to become bone ingrowth surfaces 1380, which bone ingrowth surfaces 1380 contribute to stabilizing the two joint inserts or inter-facet spacers 1310 of the implant 1300. In one preferred embodiment, the bone ingrowth surface 1380 can be created with plasma spray titanium, and/or with a coating of sintered beads In an alternative preferred embodiment, the implant 1300 can have casted porous surfaces 1370, where the porous surface is integral to the implant 1300. In a further alternative embodiment, the surfaces 1370 can be roughened in order to promote bone ingrowth into these defined surfaces of the implants 1300. In other preferred embodiments, the surfaces 1370 can be coated with materials that promote bone growth such as for example BMP, or structural materials such as HA, or other substances which promote growth of bone on other external surfaces 1370 of the implant 1300. This fixation stabilizes the implant 1300 in the facet joint without fusing the joint, and thus the implant preserves joint mobility, while accomplishing distraction and increasing forammal dimension.

Also shown in FIG. 16 are articular inner surfaces 1382 of the implants 1300. These surfaces can be formed from a metal and polyethylene, the material allowing flexibility and providing for forward bending/flexion and backward extension of the cervical spine. The embodiment 1300 of FIG. 16 can be made in at least two configurations. The first configuration includes a flexible spacer 1382 made, by way of example, using polyethylene or other suitable, flexible implant mateπal. The flexible spacer 1382 can be permanently affixed to the upper and lower joint insert or mter-facet spacer 1310. The spacer 1382 can be flat or wedge-shaped or have any other shape that would correct the curvature of the spme. In other configurations, the spacer 1382 can be affixed to only the upper insert 1310 or to only the lower insert 1310. Alternatively, a spacer 1382 can be affixed to each of an upper insert 1310 and a lower insert 1310 with the upper insert 1310 and the lower insert 1310 being separate units.

FIG. 17 shows a further preferred embodiment of the implant of the present invention. In this embodiment 1400, the implant has a roller 1496 mounted on a joint insert or mter-facet spacer 1410, the roller being a further means of preserving joint mobility while accomplishing distraction. Both the roller 1496 and the joint insert or inter-facet spacer 1410 are positioned in the cervical facet joint 1401. The joint insert or inter-facet spacer 1410 as in other embodiments has a bone-facing surface 1470 and joint articular surface 1482. The bone-facing surface 1470 can interact with the lower bone of the cervical facet joint 1401 Alternatively, the bone-facmg surface can interact with the upper bone of the cervical facet joint 1401. Between the bone-facing surface 1470 and the joint articular surface 1482 is an axis about which the roller 1496 can rotate. The roller 1496 rotates in a cavity in the j oint insert or inter-facet spacer 1410, and interacts with the top bone of the cervical facet joint 1401. Alternatively, where the bone- facing surface 1470 of the joint insert or inter-facet spacer 1410 interacts with the top bone of the cervical facet joint 1401, the roller 1496 rotates in a cavity in the joint insert or inter-facet spacer 1410 and interacts with the lower bone of the cervical facet joint 1401. The rotation of the roller 1496 allows flexion and extension of the cervical spine. Alternatively, a roller such as roller 1496 can be secured to an upper and a lower insert such as inserts 410 in FIG. 7. As depicted in FIG. 18, a plurality of rollers 1496 also is possible FIG. 19 depicts a further embodiment of the implant of the present invention. In this embodiment, two implants 1500 are implanted in the cervical facet joint 1501. Screw fixation or other appropriate fixation is used with implants 1500 for fixation in the cervical facet joint 1501. The joint insert or inter- facet spacer 1510 is continuous with a posterior sheath 1520 bent at an angle from the joint insert or lnter- facet spacer 1510 to align substantially parallel with the bone, preferably the lateral mass or lamina. The posterior sheath 1520 of each implant 1500 can have a bore 1530 which can accept a bone screw 1540, preferably into the lateral mass or lamina. Alternatively, the bore 1530 can accept any other appropriate and/or equivalent fixation means for fixing the embodiment 1500 to the spine. The head of the screw 1540 in each posterior sheath 1520 of each implant 1500 has a groove 1598 or other mechanism for retaining an elastic band 1597. The elastic band 1597 is looped around each of the two screws 1540 to restrain movement of the cervical spine without eliminating facet joint mobility. The band 1597 preferably can restrain flexion and lateral movement. The elastic band 1597 can be made of a biocompatible, flexible material.

FIG. 20 shows an alternative to use of an elastic band as in FIG. 19. In the embodiment in FIG. 20, the elastic band is replaced with a spring restraint 1699, which extends between the heads of two screws 1640, one screw fixing each of two implants 1600 in the cervical facet joint 1601.

FIG. 21 shows another alternative to using an elastic band and/or a spring as in FIGs. 19 or 20. In FIG.21, magnets 1795 is used for restraint between the two screws 1740. The magnet 1795 can either be compπsed of two opposing magnetic fields or two of the same magnetic fields to operate to restrain movement. The head of one of the two screws 1740 is magnetized, and the head of the other screw 1740 is magnetized with either the same or opposite field. If the magnets 1795 have the same polanty, the magnets 1795 repel each other and thus limit extension. If the magnets 1795 have opposite polarities, the magnets 1795 attract each other and thus limit flexion and lateral movement.

FIGs. 22A-24B, depict a further embodiment 1800 of the implant of the present invention. In this embodiment, a facet joint spacer (or insert) or inter-facet spacer (or insert) 1810 is connected with a lateral mass plate (also referred to herein as an anchoring plate) 1820 with a hinge 1822. The hinge 1822 allows the lateral mass plate 1820 to bend at a wide range of angles relative to the facet joint spacer or mter-facet spacer and preferably at an angle of more than 90 degrees, and this flexibility facilitates positioning and insertion of the facet joint spacer or inter-facet spacer 1810 into a patient's facet joint, the anatomy of which can be highly variable among individuals. This characteπstic also applies to embodiments descπbed below, which have a hinge or which are otherwise enabled to bend by some equivalent structure or mateπal property. The hinge 1822 further facilitates customizing the anchonng of the implant, i.e., the positioning of a fixation device. The hinge enables positioning of the lateral mass plate 1820 to conform to a patient's cervical spinal anatomy, and the lateral mass plate 1820 accepts a fixation device to penetrate the bone The facet joint spacer or inter-facet joint spacer 1810 can be curved or rounded at a distal end 1812 (FIG. 23A), and convex or dome-shaped on a supeπor surface 1813 to approximate the shape of the bone inside the facet joint. The inferior surface 1815 can be flat or planar. Alternatively, the infenor surface 1815 can be concave. As another alternative, the inferior surface 1815 can be convex.

The lateral mass plate 1820, when implanted in the spine, is positioned outside the facet joint, preferably against the lateral mass or against the lamma. The lateral mass plate 1820 has a bore 1830 therethrough The bore 1830 can accept a bone screw 1840, also referred to as a lateral mass screw, to secure the lateral mass plate 1820 preferably to the lateral mass or alternatively to another part of the spine, and thus to anchor the implant. The lateral mass screw 1840 preferably has a hexagonal head to accept an appropriately-shaped wrench. As described below, the head accepts a compatible probe 1826 from a locking plate 1824

The locking plate 1824 includes a keel 1828 with a wedge shaped distal end to anchor the implant, preferably in the lateral mass or in the lamina, outside the facet joint and to prevent rotation of the lateral mass plate 1820 and the locking plate 1824 The keel 1828 aligns with a groove 1823 through an edge of the lateral mass plate 1820 to guide and align the keel 1828 as the keel 1828 cuts into a vertebra

As noted above, the locking plate 1824 includes a probe 1826 that fits against the head of the lateral mass screw 1840. The locking plate further includes a bore 1831 that can accept a machine screw (not shown) which passes through to an aligned bore 1829 in the lateral mass plate 1820 to hold the locking plate 1824 and the lateral mass plate 1820 together without rotational displacement relative to each other. The locking plate 1824 thus serves at least two functions: (1) maintaining the position of the lateral mass screw 1840 with the probe 1826, so that the screw 1840 does not back out, and (2) preventing rotation of the implant with the keel 1828 and machine screw relative to the cervical vertebra or other vertebrae. It is to be understood that other mechanisms can be used to lock the locking plate 1824 to the lateral mass plate 1820. For example, the locking plate can include a probe with barbs that can be inserted into a port in the lateral mass plate The barbs can become engaged in ribs that define the side walls of the port in the lateral mass plate

In the preferred embodiment depicted in FIGs. 25A, 25B, the lateral mass plate 1920 includes a recessed area 1922 for receiving the locking plate 1924 so that the locking plate 1924 is flush with the upper surface 1925 of the lateral mass plate 1920 when the probe 1926 is urged against the lateral mass screw 1940 and the keel 1928 is inserted into the lateral mass or the lamina of the vertebra In the preferred embodiment depicted in FIGs. 25A, 25B, the shape and contours of the facet joint spacer or mter-facet joint spacer 1910 can facilitate insertion of the facet joint spacer or mter-facet joint spacer 1910 into the cervical facet joint. In this embodiment, the facet joint spacer or inter-facet joint spacer 1910 has a rounded distal end 1912. The distal end 1912 is tapered in thickness to facilitate insertion. The tapered distal end 1912 meets and is continuous with a proximal mid-section 1916 which, in this preferred embodiment, has a uniform thickness, and is connected flexibly, preferably with a hinge 1922, to the lateral mass plate 1920, as described above. The facet joint spacer (or insert) or inter-facet joint spacer (or insert) 1910, with its proximal mid-section 1916 and tapered distal end 1912, is curved downward, causing a superior surface 1913 of the facet joint spacer or mter-facet joint spacer 1910 to be curved. The curve can cause the supeπor surface 1913 to be convex, and the convexity can vary among different implants 1900 to suit the anatomical structure of the cervical facet jomt(s) of a patient. An inferior surface 1915 accordingly can be preferably concave, flat, or convex. The curved shape of the implant can fit the shape of a cervical facet joint, which is comprised of an inferior facet of an upper vertebra and a supeπor facet of a lower adjacent vertebra. The convex shape of the superior surface 1913 of the facet joint spacer or mter-facet joint spacer 1910 fits with a concave shape of the inferior facet of the upper cervical vertebrae. The concave shape of the inferior surface 1915 of the facet joint spacer or inter-facet joint spacer 1910 fits with the convex shape of the superior facet of the cervical vertebrae. The degree of convexity and concavity of the facet joint spacer or inter-facet joint spacer inferior and supeπor surfaces can be vaπed to fit a patient's anatomy and the particular pairing of adjacent cervical vertebrae to be treated. For example, a less-curved facet joint spacer or inter-facet joint spacer 1910 can be used where the patient's cervical spinal anatomy is sized (as described below) and found to have less convexity and concavity of the articular facets. Generally for the same level the input for the right and left facet joint will be similarly shaped. It is expected that the similarity of shape of the facet joint spacer or inter-facet joint spacer and the smooth, flush surfaces will allow distraction of the facet joint without loss of mobility or damage to the bones of the cervical spine. Further, and preferably, the width of the mid-section 1916 is from 1.5 mm to 2.5 mm. Except as otherwise noted above, the embodiment shown in FIGs. 22A-24B is similar to the embodiment shown in FIGs. 25A, 25B. Accordingly the remaining elements on the 1900 seπes of element numbers is preferably substantially similar to the described elements in the 1800 series of element numbers, as set forth above. Thus, by way of example, elements 1923, 1928, 1929 and 1930 are similar, respective elements 1823, 1828, 1829 and 1830. FIG. 30 is a flow chart of the method of insertion of an implant of the invention. The embodiment

1800 or 1900 of the present invention preferably is inserted in the following manner (only elements of the embodiment 1800 will be set forth herein, for purposes of the wntten description of a method of the invention). First the facet joint is accessed. A sizing tool 2200 (see FIGs. 29A-C) can be inserted to select the appropriate size of an implant of the invention for positioning in the cervical facet joint. This step may be repeated as necessary with, if desired, different sizes of the tool 2200 until the appropπate size is determined. This sizing step also distracts the facet joint and surrounding tissue in order to facilitate insertion of the implant. Then, the natural or artificial facet joint spacer or inter-facet joint spacer 1810 is urged between the facets into the facet joint. The facet itself is somewhat shaped like a ball and socket joint. Accordingly, in order to accommodate this shape, the spacer 1810 can have a rounded leading edge shaped like a wedge or tissue expander to cause distraction of the facet joint as the facet joint spacer or inter-facet joint spacer is urged into the facet joint of the spine. The natural or artificial facet joint spacer or inter-facet joint spacer 1810 also includes the convex surface 1813 in order to more fully accommodate the shape of the facet joint of the spine. However, as set forth above and as depicted in FIG. 25B, it is possible in the alternative to have a curve-shaped natural or artificial facet joint spacer (or insert) or lnter- facet joint spacer (or insert) 1910 with a convex superior surface 1913 and a concave infeπor surface 1915, the distal end 1912 tapering to facilitate insertion, while the remainder of the natural or artificial facet joint spacer or inter-facet joint spacer 1910, (i.e., the proximal section 1916) has a uniform thickness. Once the natural or artificial joint spacer 1810 is positioned, the lateral mass plate 1820 is pivoted downward about the hinge 1822 adjacent to the vertebrae and preferably to the lateral mass or to the lamma. Thus the lateral mass plate 1820 may be disposed at an angle relative to the natural or artificial facet joint spacer or mter-facet joint spacer 1810 for a representative spme configuration. It is to be understood that as this embodiment is hmged the final position of the lateral mass plate 1820 relative to the natural or artificial facet joint spacer or inter-facet joint spacer 1800 will depend on the actual spine configuration. It is to be understood that embodiments of the invention can be made without a hmge, as long as the connection between the natural or artificial facet joint spacer or inter-facet joint spacer and the lateral mass plate is flexible enough to allow the lateral mass plate to be bent relative to the natural or artificial facet joint spacer or inter-facet joint spacer in order to fit the anatomy of the patient. Once the lateral mass plate 1820 is positioned, or prior to the positioning of the lateral mass plate 1820, a bore can be drilled in the bone to accommodate the bone screw 1824 Alternatively the screw 1824 can be self- tapping. The screw is then placed through the bore 1830 and secured to the bone, preferably the lateral mass or the lamina, thereby holding the natural or artificial facet joint spacer or inter-facet joint spacer 1800 in place. In order to lock the bone screw 1824 in place and to lock the position of the natural or artificial facet joint spacer or inter-facet joint spacer 1800 and the lateral mass plate 1820 in place, the locking plate 1824 is positioned over the lateral mass plate 1820. So positioned, the probe 1826 is positioned through the bore 1830 and against the head of the bone screw to keep the bone screw from moving. The keel 1828, having a sharp chisel-shaped end, preferably can self-cut a groove in the bone so that the keel 1828 is locked into the bone as the keel 1828 is aligned by, and received in, a groove 1831 of the lateral mass plate 1820. Alternatively, a groove can be pre-cut in the bone to receive the keel 1828. As this occurs the bore 1829 of the locking plate 1824 aligns with the threaded bore 1831 of the lateral mass plate 1820 and a machine screw can be inserted to lock the locking plate relative to the lateral mass plate. This locking prevents the lateral mass plate 1820 and the natural or artificial facet joint spacer or inter-facet joint spacer 1810 from rotating and, as previously indicated, prevents the bone screw 1840 from backing out from the vertebra. Preferably the implant is between the C5 and C6 vertebrae level, or the C6 and C7 vertebrae level. It is noted that two implants preferably will be implanted at each level between vertebrae. That is, an implant 1800 will be placed in a right facet joint and also in a left facet joint when viewed from a posterior view point. This procedure can be used to increase or distract the foraminal area or dimension of the spine in an extension or in neutral position (without having a deleterious effect on cervical lordosis) and reduce the pressure on the nerves and blood vessels. At the same time this procedure preserves mobility of the facet joint.

FIGs. 26A-27B show a further embodiment of the implant of the invention, with the embodiment 2000 implanted in the cervical spine as depicted in FIGs. 27A and 27B. The implant 2000 comprises a first natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2010 and a second natural or artificial facet joint spacer or mter-facet joint spacer 2010. Each natural or artificial facetjomt spacer or mter-facet joint spacer can have a distal end 2012 that is tapered or wedge-shaped in a way that facilitates insertion into the cervical facet joints on both sides of two adjacent cervical vertebrae at the same level. The natural or artificial facet joint spacer or inter-facet joint spacers further can be dome-shaped, or convex on a supenor surface 2013, to approximate the shape of the cervical facets of the cervical facet joints.

The first and second natural or artificial facet joint spacers or mter-facet joint spacers 2010 are bridged together by a collar 2015. The collar 2015 passes between the spinous processes of the adjacent cervical vertebrae. As can be seen in FIG. 26B, the implant can preferably be "V" shaped or "boomerang" shaped. The entire implant 2000 or the collar 2015 of the implant can be made of a flexible material such as titanium, so that it is possible to bend the collar 2015 so that it conforms preferably to the shape of the lateral mass or the lamina of the cervical vertebrae of the patient and thereby holds the implant in place with the natural or artificial facet joint spacer or inter-facet joint spacers 2010 inserted in the cervical facet joints Bores 2029 are preferably are provided through implant 2000 adjacent to the natural or artificial facet joint spacer or inter-facet joint spacer 2010 respectively. These bores 2029 can receive bone screws to position the implant 2000 against the lateral mass or the lamina as shown in FIGs. 27A, 27B. The description of the embodiment 2100, in FIGs.28A, 28B provide further details concerning the method of affixing the implant 2000 to the vertebrae. The implant 2100 also can be made of PEEK or other materials as described herein. Embodiment 2000 (the "boomerang" shape depicted in FIG. 27B) further can have a locking plate as, for example, the locking plate 1824 in FIG. 22 A. The locking plate for embodiment 2000 (not shown) can have the same features as locking plate 1824, that is: (1) a probe 1826 that interacts with the bone screws to prevent the bone screws from backing out of the bone, the likely consequence of which would be displacement of the implant 2000; and (2) a keel 1828 with a chisel end to embed in the bone and thus to prevent rotational displacement of the implant. However, given the collar 2015 configuration of embodiment 2000, a chisel may not serve the same purpose as with the embodiments set forth above, which lack a collar stabilized by two bone screws. Therefore, a locking plate on embodiment 2000 can be provided without a keel.

FIGs. 28A and 28B depict a further embodiment of the implant of the invention 2100. In this embodiment 2100, the collar 2115 can be made of a flexible material such as titanium, of a substantially inflexible material, or of other materials described herein. Substantial flexibility can also be derived from connecting a first natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2110 with the collar 2115 using a first hinge 2117, and connecting a second natural or artificial facet joint spacer or inter-facet j oint spacer 2110 with the collar 2115 using a second hinge 2117. Using the first hinge 2117 and the second hinge 2117, the collar 2115 can be pivoted downward to conform to a particular patient's cervical spinal anatomy. In other words, the degree of pivoting will vary among different patients, and the first hinge 2117 and second hinge 2117 allow the implant 2100 to accommodate the variance. In the hinged embodiment 2100, and similar to the embodiment 2000, the collar 2115 can have a first bore 2129 inferior to the first hinge 2117, and a second bore 2129 inferior to the second hinge 2117. A first bone screw penetrates the first bore 2130 and into the lateral mass or the lamina, and the second bone screw penetrates the second bore 2130 and into the lateral mass or the lamina, the first and second bone screws serving to anchor the implant. A bore, preferably in the lateral mass, can be drilled for the first bone screw and for the second bone screw. Alternatively, the bone screws can be self-tapping. A first locking plate similar to the plate 1924 (FIG. 25A) can be secured about the head of the first bone screw and a second locking plate can be secured about the head of the second bone screw to prevent displacement of the first and second bone screws 2140. The first locking plate can block the first bone screw with a probe and the second locking plate can block to the second bone screw with a probe. It should be noted that embodiments 2000 and 2100 also can be configured for accommodating treatment of cervical spinal stenosis and other cervical spine ailments where only a single cervical facet joint between adjacent vertebrae requires an implant, i.e., where treatment is limited to one lateral facet joint. In that case, the collar 2015, 2115 extends medially without extending further to join a second natural or artificial facet joint spacer or inter-facet joint spacer 2010, 2110. For the hinged embodiment 2100, the implant comprises a single hinge 2117, and the collar 2115 has only one bore 2129 to accept one bone screw to secure the implant 2100.

FIGs. 29A-E, depict a sizing and distracting tool 2200 of the invention. Sizing tool 2200 has a handle 2203 and a distal head 2210 that is shaped as a natural or artificial facet joint spacer or inter-facet joint spacer (e.g., 1810) of an implant of the invention. That is, the head 2210 preferably will have essentially the same features as the natural or artificial facet joint spacer or mter-facet joint spacer 1810, but the dimensions of the head 2210 will vary from one tool 2200 to the next, in order to be able to use different versions of the sizing tool 2200 to determine the dimensions of the cervical facet joint that is to be treated and then to select an appropriately-sized implant. The head 2210 preferably can be used to distract the facet joint pπor to the step of implanting the implant in the facet joint. In this regard, the head 2210 is rounded at the most distal point 2212, and can be a tapered to facilitate insertion into a cervical facet joint. The head 2210 also can have a slightly convex superior surface 2213, the degree of convexity varying among different sizing tools 2200 in order to determine the desired degree of convexity of an implant to be implanted in the cervical facet j oint. The head 2210 may have a uniform thickness along a proximal midsection 2216. Accordingly, the inferior surface 2215 preferably can be concave. Alternatively, the proximal mid-section 2212 may be convex on the superior surface 1813 without being uniform in thickness. Thus, the inferior surface 2215 can be flat or planar. The head also can be curved.

The head 2210 has a stop 2218 to prevent over-insertion of the head 2210 of the sizing tool 2200 into the facet joint. The stop 2218 can be a πdge that separates the head 2210 from the handle 2203. Alternatively, the stop 2218 can be any structure that prevents insertion beyond the stop 2218, including pegs, teeth, and the like.

Different sizing tools 2200 covering a range of dimensions of the head 2210 can be inserted successively into a cervical facet joint to select the appropriate size of an implant to position in the cervical spine, with the appropriate convexity and concavity of natural or artificial facet joint spacer or inter-facet joint spacer. Each preferably larger head also can be used to distract the facet joint

FIG. 31A depicts a posterior view of a further embodiment 2300 of the implant of the invention Embodiment 2300, as well as all of the embodiments herein, can benefit from some or all of the advantages described herein with regard to the other embodiments described herein. Further, FIG.31 A, embodiment 2300 has a natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2310 that can have a tapered or thinned distal end 2312 so that the distal end 2312 facilitates insertion of the natural or artificial facet joint spacer or inter-facet joint spacer 2310 into a cervical facetjomt The distal end 2312 can be rounded, as seen in the plan view of FIG. 31 A, in order to conform to the roundness of the facet joint. The natural or artificial facet joint spacer or inter-facet joint spacer 2310 further can be curved so that a superior surface 2313 of the natural or artificial facet joint spacer or mter-facet joint spacer 2310 is convex, and an inferior surface 2315 is concave, to approximate the natural shape of the cervical facet joint that is to receive the implant 2300. The curve can have a uniform thickness, or it can have a varied thickness Further, the lateral edges of the natural or artificial facet joint spacer or inter-facet joint spacer 2310 are curved or rounded, for distribution of load-bearing stress. As with other embodiments described herein, the natural or artificial facet joint spacer or inter-facet joint spacer 2310 also can be made of a flexible, biocompatible mateπal, such as PEEK, to maintain joint mobility and flexibility.

The natural or artificial facet joint spacer or mter-facet joint spacer 2310 is connected flexibly with a lateral mass plate 2320, the flexible connection preferably being a hmge 2322. As seen in the plan view of FIG.31 A, the implant 2300 is substantially hour-glass shaped. This shape, as well as the shape of FIG. 32, will be discussed further below. The hinge 2322 is narrower than the natural or artificial facet joint spacer or mter-facet joint spacer 2310, with the hmge 2322 sitting at substantially the isthmus 2317 between natural or artificial facet joint spacer or inter-facet joint spacer 2310 and the lateral mass plate 2320 The curved edges, or fillets, about the hmge 2322 serve to distribute more evenly the load-bearing stress on the implant 2300, and thus prevent concentrating the stress about the edges

The hinge 2322 allows the implant 2300 to bend at the hmge 2322, bringing a lateral mass plate 2320 adjacent to the lateral mass and/or lamina of the patient's spme, and to conform to a particular patient's anatomy. The lateral mass plate 2320 is made of a biocompatible flexible material, preferably titanium or any other biocompatible flexible material as described herein, for example PEEK, that will support the use of bone screws and other hardware, as described below. The lateral mass plate 2320 bends downward at the hmge 2322 over a wide range of angles relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2310, and preferably at an angle of more than 90 degrees, and this flexibility facilitates positioning and insertion of the natural or artificial facet joint spacer or inter-facet joint spacer. This flexibility of the lateral mass plate 2320 relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2310 further facilitates positioning of the lateral mass plate relative to the lateral mass and/or the lamina of the patient's spine. Once the lateral mass plate 2320 is positioned adjacent to the bone, preferably the lateral mass of a cervical vertebra, a first bone screw, such as bone screw 1840, can be inserted through a first bore 2330 through the lateral mass plate 2320 and embedded into the bone of the lateral mass of the cervical vertebra.

The lateral mass plate 2320 further comprises a second bore 2329 which is preferably positioned medially, relative to the first bore 2330. Thus, viewing the implant from a postenor perspective as in FIG. 31 A, the second bore 2329 in the lateral mass plate 2320 can be positioned either to the left or to the right of the first bore 2330. The position of the second bore 2329 will depend upon whether the implant 2300 is intended to be inserted into a cervical facet joint on the left or right side of a patient. Specifically, an implant 2300 to be inserted into a right-side cervical facet joint (i.e., the patient's rights side) will have a second bore 2329 positioned to the left of the first bore 2330 as in FIG.31 A, when implant 2300 is viewed from a posterior perspective, while an implant 2300 to be inserted into a left-side cervical facet joint will have a second bore 2329 positioned to the πght of the first bore 2330, when implant 2300 is viewed from a posteπor perspective.

The second bore 2329 through the lateral mass plate 2320 is adapted to accept a second screw 2390 (FIG.31B), which preferably is a locking screw with a chisel point 2391. The locking screw 2390 is received by the second bore 2329 and the chisel point 2391 self-cuts a bore into the bone. The locking screw 2390 preferably is inserted through the second bore 2329 and embedded in the bone, after the bone screw is embedded in the bone through the first bore 2330. The position of the second bore 2329, i.e., medial to the first bore 2330, positions the locking screw 2390 so that it embeds in stronger bone tissue than if the second bore 2329 were located more laterally. The locking screw, in combination with the bone screw, prevents rotational and/or backward displacement of the implant 2300. As the locking screw 2390 is received by the second bore 2329, the head 2392 of the locking screw 2390 aligns with the head of the first bone screw in the first bore 2330, blocking the head of the first bone screw to prevent the first bone screw from backing out of the bone of the vertebra and the first bore 2330.

FIG.32 depicts a further embodiment 2400 of the implant of the invention, from a posteπor view. Embodiment 2400 is adapted to be implanted in a manner that preserves the anatomy of the cervical facet joint, in particular, the soft tissues around the cervical facet joint, including the joint capsule.

Implant 2400, like implant 2300 and other implants disclosed above, has a natural or artificial facet joint spacer (or inert) or inter-facet joint spacer (or insert) 2410, flexibly connected, preferably by a hinge 2422, to a lateral mass plate 2420. As can be seen m FIG 32, the implant 2400 including the natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2410 and the hinge 2422 is substantially "P" shaped. As explained below, its "P" shape assists in the insertion of the implant 2400 into the facet joint with most of the facet capsule and facet capsule ligament and other soft tissue associated with the facet joint still left intact. The natural or artificial facetjoint spacer or inter-facet joint spacer, as above for implant 2300 and the other implants disclosed above, can have a superior surface 2413 of the natural or artificial facetjoint spacer or inter-facet joint spacer 2410 that is convex, and an inferior surface 2415 that is concave, or any appropriate shaping to approximate the natural shape of the cervical facetjoint that is to receive the implant 2400. The thickness of the natural or artificial facetjoint spacer or mter-facet joint spacer 2410 can be uniform, or varied. The natural or artificial facetjoint spacer or inter-facet joint spacer 2410 also can be made of a flexible, biocompatible mateπal, such as PEEK, to maintain joint mobility and flexibility. The hinge 2422 can have smooth, rounded edges, for distribution of load stress, as disclosed above. Other features and advantages of the other embodiments can be, if desired, incorporated into the design of the embodiment of FIG. 32. For example, the natural or artificial facet joint spacer or inter-facet joint spacer 2410 further can have a tapered or thinned edge 2412 so that the edge 2412 facilitates insertion of the natural or artificial facet joint spacer or inter-facet joint spacer 2410 into a cervical facet joint. The edge 2412 can be curved. In this embodiment 2400, however, the thinned edge 2412 of the natural or artificial facet joint spacer or inter-facet joint spacer 2410 preferably is not at the distal end of the natural or artificial facet joint spacer or inter-facet joint spacer 2400 as is the thinned edge 2312 of the natural or artificial facet joint spacer or inter-facet joint spacer 2300; rather, the thinned edge 2412 preferably is positioned laterally, toward the hinge 2422 of the implant 2400. The thinned edge 2412 coincides substantially with a lateral curvature 2440 of the natural or artificial facet joint spacer or inter- facet joint spacer 2410, which is pronounced relative to the curvature on the medial side of the implant 2400, i.e., a "P" shape. In other words, the curved part of the head of the "P" 2440 corresponds to the thinned edge 2412, and serves as the leading edge of the implant 2400 to begin insertion of the natural or artificial facet joint spacer or mter-facet joint spacer 2410 into a cervical facet joint, preferably through an incision in the soft tissue of the facet joint. The "P" shape narrows at isthmus 2417 where the natural or artificial facet joint spacer or inter-facet joint spacer 2410 that is joined by the hinge 2422 with the lateral mass plate 2420. The smooth or rounded edges or fillets serve to distribute stresses on the implant 2400. The above descπbed "P" shape of implant 2400 allows the implant 2400 to be pivoted into place into a facet joint as descπbed below. The thinned edge 2412 and leading lateral curvature 2440 of the natural or artificial facet joint spacer or mter-facet joint spacer 2410 are adapted to facilitate urging implant 2400 into the cervical facet joint, through the incision in the joint capsule. The implant 2400 then is pivoted into position so that the lateral mass plate 2420 can be bent downward, relative to the natural or artificial facet joint spacer or mter-facet joint spacer 2410, to align with and he adjacent to the lateral mass and/or the lamina. The lateral mass plate 2420 is then fastened to the bone.

The lateral mass plate 2420 of implant 2400, like the lateral mass plate for implant 2300, is flexibly connected, preferably by the smooth-edged hinge 2422, to the natural or artificial facet joint spacer or inter-facet joint spacer 2410 at the narrow lower part of the natural or artificial facet joint spacer or mter- facet joint spacer. The lateral mass plate 2420 is made of a biocompatible flexible mateπal, preferably titanium or any other biocompatible flexible material such as PEEK that will support the use of bone screws and other hardware, as descπbed below.

The lateral mass plate 2420 bends downward at a wide range of angles relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2410, and preferably at an angle of more than 90 degrees. The flexibility of the lateral mass plate 2420 relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2410 further facilitates positioning of the lateral mass plate 2420 relative to the lateral mass and/or the lamma of the patient's spine. Like embodiment 2300, described above, the lateral mass plate 2420 has first bore 2430, which is adapted to receive a bone screw 2440, to help anchor implant 2400 in position. The lateral mass plate 2420 further includes a second bore 2429 adapted to be positioned medially, relative to the first bore 2430, as disclosed above for implant 2300. The position of the second bore 2429, when viewing implant 2400 from a posterior perspective (FIG.32), will depend upon whether implant 2400 is intended to be implanted into a left-side or right-side cervical facet joint of a patient. Thus, implant 2400 with the second bore 2429 positioned to the left of the first bore 2430 is intended to be implanted in a right-side cervical facet joint of a patient, as depicted in FIG.32, while an implant 2400 with a second bore 2429 positioned to the πght of the first bore 2430 is intended to be implanted in a left-side cervical facet joint of a patient.

The second bore 2429 through the lateral mass plate 2420 is adapted to receive a second screw 2490 with head 2492, which preferably is a locking screw with a chisel point, such as screw 2390. The function and purpose of the bone screw disposed through bore 2430 and the locking screw disposed through bore 2429 are as described above with respect to the implant 2300

The present invention further includes a method of implanting the implant 2400 (FIGS. 33A, 33B) To insert the natural or artificial facet joint spacer or mter-facet joint spacer 2410, a facet joint is accessed and an incision or a pair of incisions is made in the capsular ligament, the joint capsule, and the synovial membrane so that the thinned edge 2412 of the implant 2400 can be urged into the cervical facet joint through these tissues. The capsular ligament and the joint capsule and other soft tissues around the cervical facet joint are allowed to remain substantially intact, except for the small incision, and will be sutured and allowed to heal around the implant 2400 If desired, the cervical facet joint can be distracted prior to urging the curved section 2440 with the thinned edge 2412 of the natural or artificial facet joint spacer or inter-facet joint spacer 2410 into the cervical facet joint. Once the curved section 2440 of the natural or artificial facet joint spacer or inter-facet joint spacer 2410 with the thinned edge 2412 is urged into the cervical facet joint, implant 2400 is pivoted, preferably about 90 degrees, so that the second bore 2429 is placed medially relative to the first bore 2430. This allows the natural or artificial facet joint spacer or inter-facet joint spacer 2410 to be positioned in the facet joint It is noted that the overall size, including the isthmus 2417, of the natural or artificial fact joint 2410, as that of 2310, can be somewhat smaller than in prior embodiments to allow the natural or artificial facet joint spacer or inter-facet joint spacer to be positioned within the edges of the facet joint with the joint capsule substantially intact. The lateral mass plate 2420 then can be bent downward about the hinge 2422 into position adjacent the lateral mass or lamina of the spine of the patient, which position will depend upon the anatomy of an individual patient's cervical spine.

Once the lateral mass plate 2420 is positioned adjacent to the bone, preferably the lateral mass of a cervical vertebra, a first bone screw can be inserted through the first bore 2430 through the lateral mass plate 2420 and become embedded into the bone of the lateral mass of the cervical vertebra to anchor the implant 2400. After the bone screw is embedded, a locking screw is inserted through the second bore 2429 of the lateral mass plate 2420, the second bore 2429 medial to the first bore 2430. The locking screw has a chisel end that allows the locking screw to dig into the bone without use of a tool to pre-cut a bore. Alternatively, a bore can be pre-cut and a locking screw without a chisel end can be used As the locking screw is embedded in the bone, the locking head of the locking screw is brought into proximity with the head of the bone screw to block its backward movement so that the implant 2400 remains anchored with the bone screw, i.e., so that the bone screw cannot back out of the bone. The embedded locking screw also serves to prevent rotational displacement of implant 2400, while blocking backward displacement of the first bone screw.

Referring to FIGs.34A through 36B, a still further embodiment of an implant 2500 in accordance with the present invention can include a natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2510 connected with a lateral mass plate (also referred to herein as an anchoring plate) 2520 by a spheroidal joint arrangement 2538 or otherwise shaped multiple direction articulation joint arrangement. The natural or artificial facet joint spacer or inter-facet joint spacer 2510 has a load bearing structure sized and shaped to distπbute, as desired, a load applied by opposing surfaces of superior and inferior facets to one another. As shown, the load bearing structure has a saucer shape, but as described in further detail below (and as described in previous embodiments above), in other embodiments the load bearing structure can have some other shape so long as a desired load distribution and separation between superior and inferior facets is achieved. The natural or artificial facet joint spacer or inter-facet joint spacer 2510 includes a handle-like structure connected with the load bearing surface, the handle-like structure necking at an isthmus 2517 and terminating at a pivot end 2526. In an embodiment, the pivot end 2526 is substantially spherical, ovoidal, or similarly rounded in shape. As further descπbed below, the natural or artificial facet joint spacer or inter-facet joint spacer 2510 can comprise a flexible material, for example a biocompatible polymer such as PEEK, or a more rigid material, for example a biocompatible metal such as titanium. As shown, the lateral mass plate 2520 has a generally square shape with rounded corners, however, in other embodiments the lateral mass plate 2520 can have any number of shapes so long as the lateral mass plate 2520 provides sufficient support for anchoring the implant 2500 in position and so long as the lateral mass plate 2520 allows a desired range of motion for the natural or artificial facetjoint spacer or inter-facet joint spacer 2510. The lateral mass plate 2520 includes a cavity 2527 within which the pivot end 2526 is held. The spheroidal joint arrangement 2538 comprises the pivot end 2526 and the cavity 2527 and as described below allows the natural or artificial facet joint spacer or inter-facet joint spacer 2510 to tilt and swivel relative to the lateral mass plate 2520 FIG. 34A is a posterior view showing a posterior face 2532 of the lateral mass plate 2520, while

FIG. 34B is an anterior view showing an anterior face 2534 of the lateral mass plate 2520. The lateral mass plate 2520 includes an anterior notch 2524 (see FIG.35) or other indentation formed along the edge of the anterior face 2534 and a posterior notch 2522 or other indentation formed along the posterior face 2532 The posteπor and anterior notches 2522,2524 are generally aligned with one another along the edge of the lateral mass plate 2520 and are connected with the cavity 2527 The notches 2522,2524 confine movement of the natural or artificial facet joint spacer or mter-facet joint spacer 2510 in the anteπor and posterior directions relative to the lateral mass plate 2520, allowing the natural or artificial facet joint spacer or inter-facet joint spacer 2510 to tilt at varying degrees of angle in an anterior and posteπor direction. Referring to FIG. 35, the anterior notch 2524 can have a narrower width than the posterior notch 2522 which is sized to provide the pivot end 2526 of the natural or artificial facet joint spacer or inter-facet joint spacer 2510 with access to the cavity 2527 so that the pivot end 2526 can be inserted into the cavity 2527 Once the pivot end 2526 is positioned withm the cavity 2527 a plug 2528 can be mated with the lateral mass plate 2520 to lock the pivot end 2526 in place withm the cavity 2527 and to further limit freedom of movement of the natural or artificial facet joint spacer or mter-facet joint spacer 2510, particularly limiting tilting of the natural or artificial facet joint spacer or inter-facet joint spacer 2510 in a posterior direction. The plug 2528 can be press fit to the posteπor notch 2522 and further welded or otherwise fixedly fastened with the lateral mass plate 2520. A physician can select an appropnate and/or desired natural or artificial facet joint spacer or mter-facet joint spacer 2510, lateral mass plate 2520, and plug 2528 according to the motion segment targeted for implantation and/or the particular anatomy of the patient. Once an appropriate combination of components is identified, the natural or artificial facet joint spacer or inter-facet joint spacer 2510 and the lateral mass plate 2520 can be mated, and the natural or artificial facet joint spacer or inter-facet joint spacer 2510 can be locked in place by the plug 2528.

As can further be seen in FIGs. 34A through 35 the lateral mass plate 2520 has a first bore 2530 therethrough. The first bore 2530 can accept a bone screw 2540 (also referred to herein as a lateral mass screw) to secure the lateral mass plate 2520 preferably to the lateral mass, lamina, or alternatively to another part of the spme, and thus to anchor the implant 2500. The lateral mass screw 2540 preferably has a head 2542 that can accept a tool chosen for the surgical procedure whether a wrench, screwdriver, or other tool. The lateral mass plate 2520 further has a second bore 2529 which is preferably positioned medially, relative to the first bore 2530. Referring to FIG. 34A, the second bore 2529 in the lateral mass plate 2520 can be positioned either to the left or to the πght of the first bore 2530. The position of the second bore 2529 will depend upon whether the implant 2500 is intended to be inserted into a cervical facet joint on the left or right side of a patient. Specifically, an implant 2500 to be inserted into a πght-side cervical facet joint (i.e., the patient's rights side) will have a second bore 2529 positioned to the left of the first bore 2530 as in FIG. 34A, when implant 2500 is viewed from a posterior perspective, while an implant 2500 to be inserted into a left-side cervical facet joint will have a second bore 2529 positioned to the πght of the first bore 2530, when implant 2500 is viewed from a posterior perspective.

The second bore 2529 through the lateral mass plate 2520 is adapted to accept a second screw 2590 which preferably is a locking screw having a chisel point 2591. The locking screw 2590 is received by the second bore 2529 and the chisel point 2591 self-cuts a bore into the bone The locking screw 2590 is preferably inserted through the second bore 2529 and embedded in the bone after the bone screw 2540 is embedded in the bone through the first bore 2530 The medial position of the second bore 2529 relative to the first bore 2530 positions the locking screw 2590 so that it embeds in stronger bone tissue than if the second bore 2529 were located more laterally. The locking screw 2590, in combination with the bone screw 2540, prevents rotational and/or backward displacement of the lateral mass plate 2520 As the locking screw 2590 is received by the second bore 2529, the head 2592 of the locking screw 2590 aligns with the head 2542 of the first bone screw 2540 in the first bore 2530, blocking the head 2542 of the first bone screw 2540 to prevent the first bone screw 2540 from backing out of the bone of the vertebra and the first bore 2530. The posteπor face 2532 can include a recessed portion 2539, and/or the second bore 2529 can be countersunk, so that the locking screw 2590 does not protrude farther from the posteπor face 2532 than desired.

In a preferred embodiment (as shown in FIGs. 34A-37), the spheroidal joint arrangement 2538 includes a spherical pivot end 2526 and a cavity 2527 having a shape approximately conforming to the spherical pivot end 2526 so that the spheroidal joint arrangement 2538 is a ball-in-socket arrangement. The ball-in-socket arrangement 2538 allows the natural or artificial facet joint spacer or in ter-facet joint spacer 2510 to move freely relative to the lateral mass plate 2520 where the natural or artificial facet joint spacer or inter-facet joint spacer 2510 is unobstructed by the lateral mass plate 2520 For example, as shown in FIG. 36A the natural or artificial facet joint spacer or inter-facet joint spacer 2510 can tilt in an anterior direction (to position 1, for example) and can tilt in a posterior direction (to position 2, for example). As the natural or artificial facet joint spacer or inter-facet joint spacer 2510 tilts in an anterior direction, the isthmus 2517 moves within the anterior notch 2524 so that the natural or artificial facet joint spacer or mter-facet joint spacer 2510 can continue tilting without obstruction. Conversely, as the natural or artificial facet joint spacer or inter-facet joint spacer 2510 tilts in a posterior direction (to position 2, for example), the isthmus 2517 contacts the plug 2528, limiting the amount of tilt of the natural or artificial facet joint spacer or inter-facet joint spacer 2510 in a posterior direction.

Referring to FIG. 36B, the ball-and-socket arrangement allows the natural or artificial facet joint spacer or inter-facet joint spacer 2510 to swivel (to position 3, for example) relative to the lateral mass plate 2520, potentially providing a more conformal arrangement of the natural or artificial facet joint spacer or inter-facet joint spacer 2510 with the surfaces of the supeπor and inferior facets Further, the ability of the natural or artificial facet joint spacer or in ter-facet joint spacer 2510 to swivel can increase options for lateral mass plate 2520 anchor positions. A physician can anchor the lateral mass plate 2520 in a more conformal or advantageous orientation and/or position along the lateral mass, for example, by alteπng the arrangement of the lateral mass plate 2520 relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2510. The amount of swiveling accommodated (and the degree of freedom of movement accommodated in general) depends on the geometries of the components. For example, where the isthmus 2517 is sufficiently narrow and long in length, a greater degree of swiveling in combination with tilt can be achieved, or for example where the plug 2528 extends over a portion of the natural or artificial facet joint spacer or inter-facet joint spacer 2510, as shown in FIGs. 36A and 36B, the amount of tilt possible in the posterior direction can be limited. One of ordinary skill in the art will appreciate that the freedom of movement of the natural or artificial facet joint spacer or inter-facet joint spacer 2510 relative to the lateral mass plate 2520 is limited substantially or wholly by the geometries of the components, and therefore can be substantially altered to achieve a desired range of movement. The ball-and-socket arrangement need not include a ball that extends from the natural or artificial facet joint spacer or inter-facet joint spacer and a socket that is formed in the lateral mass plate. For example, the ball of such a joint can extend from a locking or anchoring plate and the socket can be included in the natural or artificial facet joint spacer or inter-facet joint spacer. Further, while the preferred embodiment has been described as a ball-and-socket arrangement, other arrangements can be employed with varied results. It should not be inferred that embodiments in accordance with the present invention need include a spheroidal shaped end mated with a rounded cavity. The scope of the present invention is not intended to be limited to ball-and-socket arrangements, but rather is intended to encompass all such arrangements that provide a plurality of degrees of freedom of movement and substitutability of components. Referring again to FIGs. 36A and 36B, the load bearing structure of the natural or artificial facet joint spacer or inter-facet joint spacer 2510 includes a superior surface 2513 having a generally convex shape and an inferior surface 2514 having a slightly concave shape. The shape of the load beaπng structure is intended to approximate a shape of opposing surfaces of the superior and inferior facets The shape of the supeπor and inferior surfaces 2513,2514 can vary between motion segments and between patients. For example, as shown in FIG.37, where the cervical vertebra includes an infeπor facet having a substantially convex natural surface, a physician may select a natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2610 including a load bearing structure with an infeπor surface 2614 having a more concave shape combined with a lateral mass plate 2620 having a bone screw 2640 more appropriately sized for the particular lateral mass to which it will be fixed. (As shown the bone screw 2640 has a shorter length and wider diameter ) A physician can be provided with a natural or artificial facet joint spacer or inter-facet joint spacers having a multiplicity of load bearing structure shapes. As mentioned above, the ability to match different natural or artificial facet joint spacer or mter-facet joint spacers with different lateral mass plates can improve a physician's ability to provide appropnate treatment for a patient, and can further provide the physician flexibility to reconfigure an implant once a surgical site has been exposed and the physician makes a determination that a different combination of components is appropnate.

In yet another embodiment, the spheroidal joint arrangement 2538 of FIGs.34A-37 can be applied to collar structures, for example as shown in FIGs. 26A-27B so that the natural or artificial facet joint spacer or inter-facet j oint spacers at each end of the collar structure include an increased range of motion to improve surface matching between the natural or artificial facet joint spacer or inter-facet joint spacers and the surfaces of the superior and inferior facets (i.e., increasing the amount of facet surface area contacting the natural or artificial facet joint spacer or inter-facet joint spacers).

FIG.38 is a flow chart of an embodiment of a method in accordance with the present invention for implanting an implant as described in FIGs.34A through 37. An incision must first be made to expose the surgical site and access the targeted facet joint (Step 2500). Once the facet joint is made accessible, the facet joint can be sized and distracted (Step 2502). A sizing tool 2200 (for example, see FIGs.29A-C) can be inserted to select the appropriate size of an implant 2500 of the invention for positioning in the cervical facet joint. This step may be repeated as necessary with, if desired, different sizes of the tool 2200 until the appropnate size is determined. This sizing step also distracts the facet joint and surrounding tissue in order to facilitate insertion of the implant 2500. Once the appropriate size is determine, the physician can select an appropriate natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2510 with the lateral mass plate 2520 (Step 2504). The natural or artificial facet joint spacer or inter-facet joint spacer 2510 can then be urged between the facets into the facet joint (Step 2510). The facet itself is somewhat shaped like a ball and socket joint. Accordingly, in order to accommodate this shape, the natural or artificial joint 2510 can have a rounded leading edge shaped like a wedge or tissue expander to cause distraction of the facet joint as the natural or artificial facet joint spacer or mter-facet joint spacer is urged into the facet joint of the spine. The natural or artificial facet joint spacer or inter-facet joint spacer 2510 also includes the convex superior surface 2513 in order to more fully accommodate the shape of the facet joint of the spine. However, as set forth above and as depicted in FIG.37, it is possible in the alternative to have a curve-shaped natural or artificial facet joint spacer or inter-facet joint spacer 2610 with a convex superior surface 2613 and a concave inferior surface 2614, the distal end of the natural or artificial facet joint spacer or inter-facet joint spacer 2610 tapering to facilitate insertion, while the remainder of the natural or artificial facet joint spacer or inter-facet joint spacer 2610 has a uniform thickness.

Once the natural or artificial joint 2510 is positioned, the lateral mass plate 2520 is tilted and/or swiveled so that the lateral mass plate 2520 is adjacent to the vertebrae and preferably to the lateral mass or to the lamina (Step 2512). Thus the lateral mass plate 2520 may be disposed at an angle relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2510 for a representative spine configuration. It is to be understood that the final position of the lateral mass plate 2520 relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2510 will depend on the actual spine configuration. Once the lateral mass plate 2520 is positioned, or prior to the positioning of the lateral mass plate 2520, a bore can be drilled in the bone to accommodate the bone screw 2540. Alternatively the screw 2540 can be self-tapping. The screw 2540 is then placed through the first bore 2530 and secured to the bone, preferably the lateral mass or the lamina, thereby holding the natural or artificial facet joint spacer or mter-facet joint spacer 2510 in place (Step 2514) In order to lock the bone screw 2540 in place and to lock the position of the natural or artificial facet joint spacer or inter-facet joint spacer 2510 and the lateral mass plate 2520 in place, a self-tapping locking screw 2590 is positioned within a second bore 2529 of the lateral mass plate 2520 and secured to the bone, thereby resisting undesirable movement of the lateral mass plate 2520 (Step 2516). A head 2592 of the locking screw 2590 can further block movement of the bone screw 2540 by trapping the bone screw head 2542 between the locking screw head 2592 and the first bore 2530. The locking screw 2590 therefore prevents the lateral mass plate 2520 and the natural or artificial facet joint spacer or inter-facet joint spacer 2510 from rotating and, as previously indicated, prevents the bone screw 2540 from backing out from the vertebra. Preferably the implant is between the C5 and C6 vertebrae level, or the C6 and C7 vertebrae level. It is noted that two implants preferably will be implanted at each level between vertebrae. That is, an implant will be placed in a right facet joint and also in a left facet joint when viewed from a posterior view point. This procedure can be used to increase or distract the foraminal area or dimension of the spine in an extension or in neutral position (without having a deleteπous effect on cervical lordosis) and reduce the pressure on the nerves and blood vessels. At the same time this procedure preserves mobility of the facet joint.

FIG. 39A depicts a posterior view of another embodiment 2600 of the implant of the invention. Embodiment 2600, as well as all of the embodiments herein, can benefit from some or all of the features and advantages with regard to the other embodiments descπbed herein. As shown, embodiment 2600 has a natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2610 that can have a tapered or thinned distal end 2612. The natural or artificial facet joint spacer or inter-facet joint spacer 2610 further can be curved so that a superior surface 2613 of the natural or artificial facet joint spacer or mter-facet joint spacer 2610 is convex, and an infeπor surface 2615 is concave, to approximate the natural shape of the cervical facet joint that is to receive the implant 2600. In one embodiment, the inferior surface 2615 is substantially flat whereby the superior surface 2613 is convex (FIG. 39B). As shown in FIG. 39B, the convex superior surface 2613 tapers downward at an increased angle toward the inferior surface 2615 at the distal end 2612. This contour of the superior surface 2513 aids in smooth insertion of the natural or artificial facet joint spacer or inter-facet joint spacer 2610 into the facet joint As with other embodiments described above, the natural or artificial facet joint spacer or mter-facet joint spacer 2610 also can be made of a flexible, biocompatible material, such as PEEK, to maintain joint mobility and flexibility.

The natural or artificial facet joint spacer or inter-facet joint spacer 2610 is connected flexibly with the lateral mass plate 2620, preferably with a hinge 2622. The hmge 2622 allows the natural or artificial facet joint spacer or inter-facet joint spacer 2610 and the lateral mass plate 2620 of the implant 2600 to bend with respect to one another between an extended position and a bent or folded position as discussed above. Once the lateral mass plate 2620 is positioned adjacent to the bone, preferably the lateral mass of a cervical vertebra, a first bone screw, such as bone screw 1840, can be inserted through a first bore 2630 through the lateral mass plate 2620 and embedded into the bone of the lateral mass of the cervical vertebra. In addition, once the lateral mass plate 2620 is secured with the first bone screw, a second bone screw can be inserted through a second bore 2629 in the lateral mass plate 2620, whereby the second bone screw would be embedded into the bone of the lateral mass of the cervical vertebra Details of the first and second bores are discussed above.

The lateral mass plate 2620 is made of a biocompatible flexible material, preferably titanium or any other biocompatible flexible material as descπbed herein, for example PEEK, that will support the use of bone screws and other hardware, as described below. The lateral mass plate 2620 bends downward about the hinge 2622 over a wide range of angles relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2610. In another embodiment, any other type of interface between the natural or artificial facet joint spacer or mter-facet joint spacer 2620 and the lateral mass plate 2610 is contemplated (e.g. ball and socket joint). This flexibility facilitates positioning and insertion of the natural or artificial facet joint spacer or inter-facet joint spacer 2610

FIG.39B depicts a side view of the natural or artificial facet joint spacer or inter-facet joint spacer and lateral mass plate in accordance with one embodiment As shown in FIG.39B, the natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2610 includes an hyper-extension tab 2622 in one embodiment. The hyper-extension tab 2622 prevents the natural or artificial facet joint spacer or inter-facet joint spacer 2610 as well as the lateral mass plate 2620 from moving in a direction beyond the extended position which is shown in FIGS.39A and 39B The lateral mass plate 2620 preferably includes a recess 2611 at the interface between the lateral mass plate 2620 and the natural or artificial facet joint spacer or inter-facet joint spacer 2610 which seats the tab 2622 in the extended position which is shown in FIG. 39A. When the natural or artificial facet joint spacer or inter-facet joint spacer 2610 is bent at an angle, the tab 2622 is not in contact with the recess 2611. However, the tab 2622 comes into contact with the recess 2611 when in the extended position, as shown in FIG. 39A. In addition, the tab 2622, when seated in the recess 2611, prevents the natural or artificial facet joint spacer or inter-facet joint spacer 2610 and lateral mass plate 2620 from moving beyond the extended position. This features aids in placing the implant into the facet joint as the implant is prevented from bendng back beyond the extended position shown in FIG.39B. This arrangement, however, allows the lateral mass plate 2620 to bend down to meet the spine when the natural or artificial facet joint 2610 is implanted in the facet joint.

As shown in FIG.39A, the lateral mass plate 2620 preferably includes a third bore 2602 located near a rear edge, whereby the third bore 2602 preferably receives an engaging rod 2716 (FIG. 40B) of an implantation tool 2600 described below. The third bore 2602 preferably extends through the superior and inferior surfaces of the lateral mass plate, although not necessarily. Although the third bore 2602 is circular in shape, any other shape is contemplated which engages a correspondingly shaped engaging rod 2716 (FIG. 40B). The rear edge 2604 of the lateral mass plate 2620 can be engaged by the engagement head 2706 (FIG. 40B) of the implantation tool 2700 as described below.

In addition, the lateral mass plate 2620 preferably includes one or more winged protrusions, such as tabs, wmglets or ears, 2608 which protrude from the side edges of the lateral mass plate 2620. FIG. 39A illustrates the implant 2600 having two wmged protrusions 2608. The protrusions 2608 serve as guides to successfully couple the implant 2600 to the implantation tool 2700. In addition, the protrusions act as an engaging mechanism which secures the implant 2600 to the tool 2700. It should be noted that the winged protrusions 2608 are preferred and the implant 2600 can be configured in any other appropπate design to ensure that the implant 2600 is able to be effectively guided and secured to the implantation tool 2700.

FIG. 4OA depicts an implantation tool in accordance with one embodiment of the present invention. As shown in FIG.40A, the tool 2700 preferably includes a handle 2702 having a proximal end and a distal end. The tool 2700 includes an actuating switch 2708 as well as a shaft 2704 extending from the distal end of the handle 2702 As shown in FIG. 4OA, the shaft 2704 preferably extends axially with the handle 2702, although the shaft 2704 may be at an angle with respect to the handle 2702. Extending from the shaft 2704 is an engagement head 2706, whereby the engagement head is preferably oπented at an angle with respect to the shaft 2704 and/or the handle 2702. The angle of the head 2706 relative to the shaft 2704 aids the surgeon in the process of implanting the implant 2600 in the spine. This angle allows the surgeon to slip the natural or artificial facet joint spacer or inter-facet joint spacer 2620 into the facet joint with the tool 2700 preferably about a right angle to the spine. Preferably the head is at an angle between 45 and 90 degrees relative to the handle 2704. However, other angles are contemplated.

Referring to FIG. 4OB, the engagement head 2706 preferably has a forked configuration and includes a pair of side walls 2710, an engagement seat 2712 as well as a receiving space 2718 which is defined as the area between the side walls 2710 and the seat 2712. The engagement head 2706 preferably includes a retractable engaging rod 2716 which extends partially into the receiving space 2618. The side walls 2610 each have an inner side which includes a slot 2712 whereby the slots 2712 face the receiving space 2718. The slots 2712 are dimensioned to slidably receive the wing protrusions 2608 of the lateral mass plate 2620 as well as secure the lateral mass plate 2620 to the engagement head 2706. The engagement seat 2712 receives the rear edge 2604 of the lateral mass plate 2620. In one embodiment, the engagement head 2706 preferably includes the engaging rod 2716, as shown in FIG. 4OB. The engaging rod 2716 is dimensioned to fit within the third bore 2602 in the lateral mass plate 2620. The engaging rod 2716 is coupled the switch 2708 on the handle 2702, whereby actuation of the switch 2708 causes the engaging rod 2716 to retract. Upon being retracted, the engaging rod 2716 disengages the third bore 2602 and allows the implant 2600 to be disengaged from the engagement head 2706. It is preferred that the tool 2700 includes a spπng or other urging means to urge the engaging rod 2716 to the extended position, as shown in FIG. 4OB. In another embodiment, the engaging rod 2716 is freely moveable between the extended and retracted positions without a biasing force applied thereto.

It should be noted that the engaging rod 2716 is shown as being a circular cylinder in FIGS. 4OA and 4OB. However, it is contemplated that the engaging rod 2716 can have any other shape which conforms to the shape of the third bore 2602 in the lateral mass plate 2620. In another embodiment, the engagement head 2706 does not include an engaging rod 2716 but some other mechanism to secure the implant 2600 to the tool 2700. In yet another embodiment, the slots 2712 in the side walls 2710 can be used to retain the implant 2600 in the head 2706 without the use of an engaging mechanism. In preferred operation, to engage the implant 2600 with the tool 2700, the implant 2700 is oπented to be right side up such that the rear surface 2604 of the implant 2600 will conform and mate with the engagement seat 2714. The implant 2600 is aligned with the forked portion of the engagement head 2706, whereby the winged protrusions 2608 of the implant 2600 are inserted into the slot openings 2712. Upon registenng the wmged protrusions 2608 into the corresponding slots 2712, the lateral mass plate 2620 is guided into engagement by the slots 2712 until the rear edge 2604 mates with the engagement seat 2714. Preferably the engaging rod 2716 is then inserted into the third bore 2602, thereby secuπng the lateral mass plate 2620 to the engagement head 2706. In one embodiment, the user manually actuates the switch 2708 to retract the engaging rod 2716 to allow the lateral mass plate 2620 to be inserted completely in the receiving space The switch 2708 is then manually released when the bore 2602 and engaging rod 2716 are aligned such that the engaging rod 2716 then extends and engages the third bore 2602. In another embodiment, contact between the supeπor surface of the lateral mass plate 2620 and the engaging rod 2716 causes the engaging rod 2716 to slightly retract while the plate 2620 is moved into the engagement seat 2714. Once the lateral mass plate 2620 is seated, the third bore 2602 preferably registers with the engaging rod 2716, whereby the urging force causes the engaging rod 2716 to automatically engage the third bore 2602.

During the surgical procedure, the natural or artificial facet joint spacer or inter-facet joint spacer 2610 is inserted into the distracted facet joint as described in detail above. Upon the natural or artificial facet joint spacer or inter-facet joint spacer 2610 being satisfactorily inserted in the facet joint, the user preferably actuates the switch 2708 to disengage the engaging rod 2716 from the third bore 2602. The surgeon then draws the tool 2700 away from the facet joint, whereby the lateral mass plate 2620 slides out of the received area and is guided by the slots 2712. The lateral mass plate 2620 is then anchored into the vertebral body as discussed above. In still other embodiments, some other structure can be employed to resist movement of the seated bone screw within the first bore. Referring to FIGs. 41 A and 41B, in some embodiments a cam 2824 can be rotatably associated with the lateral mass plate 2820 so that the first bore 2830 can be selectably obstructed or unobstructed, thereby allowing a bone screw 2840 to be received within the first bore 2830, or resisting movement of the bone screw 2840 seated withm the first bore 2830. As shown in FIG. 41 A, the cam 2824 can have a shape such that at a first position the surface 2828 of the cam is approximately flush with the first bore 2830, thereby allowing a bone screw 2840 to pass through the first bore 2830. Rotated to a second position (FIG. 41B), a protruding portion 2826 of the surface of the cam 2824 can extend across at least a portion of the first bore 2830, thereby blocking a bone screw 2840 seated withm the first bore 2830 and preventing the bone screw 2840 from backing out of the first bore 2830. The cam 2824 can include features 2831 (e.g., indentations) that can allow the cam to be grasped with a tool (not shown), and thus rotated to the desired position. As shown, the cam 2824 is positioned within a slot of the lateral mass plate 2820 so that the cam does not protrude undesirably from the surface of the lateral mass plate 2820. Except as otherwise noted above, the embodiment shown in FIGs. 22A-24B is similar to the embodiment shown in FIGs. 41A-41B

A further embodiment of an implant 2900 in accordance with the present invention is shown in FIGs.42A-42G The implant 2900 resembles implants as shown in FIGs. 22A-25A in that the natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 2910 has limited freedom of movement relative to the lateral mass plate 2920. As can be seen, a hinge 2922 connects the natural or artificial facet joint spacer or inter-facet joint spacer 2910 with the lateral mass plate 2920, allowing the natural or artificial facet joint spacer or inter-facet joint spacer to pivot up and down relative to a plane of the lateral mass plate 2920 However, in other embodiments the natural or artificial facet joint spacer or inter-facet joint spacer 2910 can be connected with the lateral mass plate 2920 by way of a spheroidal joint arrangement (as described above) or by way of some other structure An inferior surface 2915 of the natural or artificial facet joint spacer or inter-facet joint spacer 2910 includes a plurality of cleats (also referred to herein as protrusions) 2986 extending from the inferior surface 2915. In one example as seen in Fig 42A the cleats point in a direction that is opposed to the direction of insertion of the natural or artificial joint in the facet joint in order to ease the insertion step and to aid in preventing the natural or artificial facet joint spacer or inter-facet joint spacer from backing out of the facet joint. Additionally the cleats or protrusions have, in one embodiment, a thickness that is less that the thickness of the natural or artificial facet joint spacer or inter-facet joint spacer defined between a superior surface of the natural or artificial facet joint spacer or inter-facet joint spacer and an infeπor surface of a natural or artificial facet joint spacer or inter-facet joint spacer. The plurality of cleats 2986 can penetrate or grip a superior facet if a kiwer vertebre of the targeted facetjoint, thereby reducing slippage of the natural or artificial facet joint spacer or inter-facet joint spacer 2910 relative to the superior facet. The cleats 2986 do not directly restrict the infenor facet of an upper vertebre of the targeted facet joint from moving along the superior surface 2913 of the natural or artificial facet joint spacer or inter-facet joint spacer 2910. The cleats 2986 can further promote bone growth by roughing the surface, which can provide beneficial results where an increase in surface contact resulting in a reduction of slippage is desired. In a preferred embodiment the natural or artificial facet joint spacer or mter-facet joint spacer 2910 can include a infeπor surface 2915 connected with the hinge 2922 and formed of a light-weight, bio-compatible material having a desired strength, such as titanium, titanium alloys, aluminum, aluminum alloys, medical grade stainless steel, etc. Such a structure is also referred to herein as an inferior shim 2980 As shown, a substantial portion of the natural or artificial facetjoint spacer or mter-facet joint spacer 2910 including the supeπor surface 2913 can be formed of a biocompatible polymer, such as described below Such a substantial portion is also referred to herein as a supeπor shim 2982 Such a material is radiolucent, and can have a desired smoothness and reduced compressive strength relative to the infeπor surface 2915 such that the superior surface 2913 of the natural or artificial facet joint spacer or inter-facet joint spacer 2910 allows for a desired slippage relative to the inferior facet of the facet joint. A superior surface 2913 having a reduced compressive strength and an increased elasticity relative to a bony structure of the spme. The supeπor shim 2982 can be molded onto the inferior shim 2980 to form the natural or artificial facet joint spacer or inter- facet joint spacer 2910, or the superior shim 2982 can be adhesively fastened to the infeπor shim 2980, interference fit with optional protuberances of the infeπor shim 2980, etc. One of ordinary skill in the art will appreciate the different techniques for fixedly connecting a supeπor shim 2982 with the inferior shim 2980.

It is also to be understood that the inferior shim can be comprised of a πgid material while the superior shim can be comprised of a more compliant and/or compressible mateπal. Thus the mfeπor shim can carry the load experienced in the facet joint while the supeπor shim can be more compliant The natural or artificial facet joint spacer or inter-facet joint spacer can, for example, be compπsed of one material that has been formed to have a gradient of stiffness from more stiff in the area of the infeπor shim to less stiff and more compliant I the area of the superior shim. For example a PEEK polymer mateπal as descπbed below can be formed in the area of the infeπor shim with fillers that increase the stiffness and strength of the material while the PEEK polymer in the area of the superior shim does not have such fillers and is thus more compliant.

In a preferred embodiment, the cleats 2986 of the implant 2900 can extend from the inferior surface 2915 to have a sawtooth shape and arrangement to resist movement in a generally posterior direction away from the facet joint (i.e., toward the lateral mass plate 2920 as shown) and further to resist movement in a lateral direction relative to the facet joint. However, the cleats 2986 need not necessarily be sawtooth in shape and arrangement. For example, the cleats 2986 can have a conical shape, a pyramid shape, a curved shape, etc. Further, as shown particularly in FIG. 42C four cleats 2986 extend from the infeπor surface 2915. In other embodiments, any number of cleats 2986 can be provided, the cleats 2986 being similarly sized and shaped, or varying in size and shape. In reflection on the teachings contained herein, one of ordinary skill in the art will appreciate the myriad different shapes with which the cleats 2986 can be formed. The cleats 2986 can vary in performance and technique for implantation with shape and number; however, the present invention is meant to encompass all such vanations

The implant 2900 can further optionally include plate cleats 2988 extending from a surface of the lateral mass plate 2920 substantially contacting the bony structures of the spme (e g., the lateral mass). The plate cleats 2988 can help anchor the lateral mass plate 2920 in position either to assist in resisting shifting as a bone screw 2940 is associated with the bony structure, or as an adjunct to the bone screw 2940 Surface roughening caused by the plate cleats 2988 can further promote bone growth near and/or integrally with the lateral mass plate 2920 As shown particularly in FIG.42C there are four plate cleats 2988, each plate cleat 2988 having a conical structure. However, as above the plate cleats 2988 can vary in size, number and shape. For example, the plate cleats 2988 can have a saw-tooth shape, a pyramid shape, a curved shape, etc.

Referring to FIGs.42D through 42G, a bone screw 2940 of the implant 2900 can be arranged in a bore 2930 so that the bone screw 2940 and bore 2930 permit a relative degree of freedom of movement resembling a ball-m-socket joint. Such an arrangement can allow for flexibility in fastening the implant 2900 to a bony structure, thereby allowing a surgeon to avoid diseased or fragile bony structures, fastening the implant 2900 to more durable, healthy bony structures. The bone screw 2940 can swivel within the bore 2930 toward or away from the natural or artificial facet joint spacer or inter-facet joint spacer 2910 and/or from side-to-side relative to the natural or artificial facet joint spacer or inter-facet joint spacer 2910. When the bone screw 2940 is arranged as desired a retaining plate 2924 (FIG.42B) can be attached to the lateral mass plate 2920 to resist backing out of the bone screw 2940, similar to the functioning of features as shown in previous embodiments. As can be seen in FIG. 42B, retaining plates 2924 can have a projection 2925 that fits in a recess 2927 of the lateral mass plate 2920 in order to prevent rotation of the retaining plate 2924 once bone screw 2940 is tightened against retaining plate 2924

Referring to FIG. 43, in still further embodiments, implants in accordance with the present invention can have both an inferior surface 3015 and a superior surface 3013 having cleats 3086 extending therefore Such embodiments can be employed, for example, to fuse the facet joint. The cleats 3086 can resist relative movement of the inferior and superior facets, and can further promote bone growth through roughening of the facet surface, thereby promoting fusion of the facet joint. The natural or artificial facet joint spacer (or insert) or inter-facet joint spacer (or insert) 3010 can be formed from a light-weight, high strength, biocompatible material such as titanium, titanium alloys, aluminum, aluminum alloys, medical grade stainless steel, etc. Alternatively, the natural or artificial facet joint spacer or inter-facet joint spacer 3010 can be formed from a biocompatible polymer, as described below, or the natural or artificial facet joint spacer or inter-facet joint spacer 3010 can comprise inferior and superior shims (not shown) fixedly connected and formed of the same or different materials. Upon reflection of the teachings herein, one of ordinary skill in the art will appreciate the different ways in which the natural or artificial facet joint spacer or inter-facet joint spacer 3010 can be formed.

As described above in reference to FIGs. 42A-G, the cleats 3086 are saw-tooth in shape and arrangement, but alternatively can have some other shape and/or arrangement. For example, the cleats 3086 can have a pyramidal shape, a curved shape, a conical shape, etc Further, the shape, size and arrangement for cleats 3086 of the inferior surface 3015 can be different or the same from cleats 3086 of the superior surface 3013 The shape, size, and arrangement of the cleats 3086 can be chosen based on the location of implantation, the preferences of the surgeon, the physical condition of the target facet joint, etc.

FIG.40 is a flow chart of an embodiment of a method in accordance with the present invention for implanting an implant as described in FIGs. 34A through 39.

FIG. 44 illustrates a side view of a distractor tool in accordance with one embodiment of the present invention. As shown in FIG.44, the distractor tool 203 preferably includes a handle portion 202, an arm portion 204, and a distractor head portion 206. In particular, the handle portion 202 preferably includes a first handle 202 A and a second handle 202B. The proximal ends of each handle 202 A, 202B preferably include finger loops 212 A and 212B, respectively. The handles 202 A and 202B are coupled to one another at a pin 208. In a preferred embodiment, the first handle 202A is moveable whereas the second handle 202B is stationary with respect to the first handle 202A. In another embodiment, the second handle 202B is able to be pivotably rotated with respect to first handle 202A about pin 208. Alternatively, both handles are movable with respect to one another about pm 208.

As shown in the embodiment in FIG. 44, the arm portion 204 has a first arm 204A and a second arm 204B. The arms 204 are oriented longitudinally along the X-axis. The upper arm 204B is preferably attached to the second handle 202B. However, the second arm 204B can alternatively be attached to the first handle 202A. In the embodiment in FIG. 44, the first arm 204A and the second handle 202B are of one formed piece. Alternatively, the first arm 204A and the second handle 202B are two separate pieces which are coupled together.

As stated above, the first handle 202A is rotatable about pin 208, whereby the pin 208 is preferably located between the midpoint and a distal end of the handle 202A. In one embodiment shown in FIG. 3A and 3B, a proximal end of the first arm 204A is coupled to the distal end of the first handle 202A at pin

210. In another embodiment, the distal end of the handle 202A is coupled to an intermediate link which couples the handle 202A to the first arm 204A.

The first handle 202 A is preferably moveable about pin 208 between an non-distracted position, as shown in FIG. 44, and a distracted position as shown in FIG. 45. As shown in FIG. 44, the first handle

202A is oriented at angle a with respect to the X-axis. In addition, the second handle 202B is oriented at angle β with respect to the X-axis. In FIG. 44, the angle a of the first handle 202 A in the non-distracted position is greater than the angle φ of the first handle 202A in the distracted position. It is preferred that, as the handles 202A, 202B are squeezed together, the tool 203 actuates from an non-distracted position to a distracted position.

When the handles 202A, 202B of the tool 203 are squeezed together, the clockwise rotational movement of the handle 202A about the pin 208 causes the distal end of the handle 202A to move the first arm 204A longitudinally along the positive X-axis (FIG.45). In contrast, when the handle 202 is released or when manually actuated to the non-distracted position, the counter-clockwise rotational movement of the handle 202A causes the distal end of the handle 202A to move the first arm 204A in the opposite direction, along the negative X-axis (FIG 44). The longitudinal movement of the first arm 204A along the X-axis causes the distraction head 206 to actuate and thus separate adjacent facets apart to allow implantation of the implant.

The distal ends of the first and second arms 204 A, 204B are coupled to the distraction head 206 as shown in FIGs.44 and 45. The distraction head 206 preferably includes a first distraction head component 206A and a second distraction head component 206B. In one embodiment, the distal end of the first arm 204 A is coupled to the first distraction head component 206 A and the first distal end of the second arm 204B is coupled to the second distraction head component 206B. In another embodiment, the distal end of the first arm 204A is coupled to the second distraction head 206B and the distal end of the second arm 204B is coupled to the first distraction head 206B. Since the first arm 204A is attached to the first distraction head component 206A, the movement of the first arm 204A along the X-axis preferably causes the first distraction head component 206A to also move along the X-axis. The second head component 206B is preferably fixed to the second arm 204B. Therefore, the movement of the arm 204along the positive X-axis causes the first head component 206A to move preferably away from the second head component 206B The first head component 206A and the second head component 206B preferably separate the adjacent facets apart between 1.5 and 2.5 mm to accommodate the thickness of the natural or artificial joint facet or inter-facet joint spacer of the implant. However, other distances are contemplated and are not limited to that described above.

In the preferred embodiment, the distal portion of the distraction head extends substantially perpendicular to the arms 204A, 204B, as shown in FIGs.44 and 45. In another embodiment, the supeπor and inferior surfaces of the distraction head extend at an angle other than 90 degrees from the arms 204 A and 204B. In the preferred embodiment shown in FIGs.44 and 45, the head components 206A, 206B of the distraction head 206 are oriented such that the leading edge 230 extends in the negative Y direction. Alternatively, the distraction head 206 is oriented such that the leading edge faces the positive Y direction. However, it is contemplated that the distraction head 206 can be oriented to extend from the arm 202 such that the leading edge faces the Z direction, as shown in FIGs. 48A and 48B. It is contemplated that the leading edge 230 of the distraction head 206 of the present invention can face any direction with respect to the arms 204 and the handles 202 including the negative Z direction.

The tool 203 of the present invention is preferably made from a medical grade metal. For example, the tool 203 can be made of titanium, stainless steel, an alloy or any other material which provides the tool 203 with a sufficient amount of strength to distract the adjacent facets apart during the implantation process. In one embodiment, the distraction head 206 is removable from the distal ends of arms, such that different sized distraction heads can be used with the same tool. This feature would allow the surgeon to replace the distraction head with one of a different size for a different inter-cervical facet joint without having to use a different tool. In another embodiment, the distraction head 206 is mounted to the arms 204 of the tool 203, whereby the upper head component 206A is welded to the lower arm 204A and the lower head component 206B is welded to the upper arm 204B or vice versa. Any other appropriate method of attaching the distraction head 206 to the arms 204 is contemplated.

It is preferred that the tool 203 includes a movement limitation mechanism. The mechanism preferably limits the amount of distraction between the first and second head components 206A, 206B when the handles 202 are actuated. As shown in FIGs.44 and 45, the proximal end of the first arm 204A preferably has a wedge-shaped portion 216. In addition, the second arm 204B includes a correspondingly shaped slot 218 which receives the wedged portion 216 duπng movement of the wedged portion 216 in the positive X direction. The slot 218 limits longitudinal movement of the first arm 204 A along the X-axis when the handles 202 are squeezed. This, in effect, limits the distance that the head components 206A, 206B separate in distracting the facets apart from one another during the implantation procedure. Alternatively, any other mechanism is contemplated to limit movement of the distraction head 206 and is not limited to the wedged portion 216 and corresponding slot 218 of the present tool. It should be noted that the movement limitation mechanism is alternatively not incorporated in the tool of the present invention. FIG. 46A illustrates a perspective view of the distraction head 206 in a distracted position in accordance with one embodiment. FIG.46B illustrates a perspective view of the distraction head 206 in FIG. 46A in a non-distracted position. As shown in FIGs. 46A and 46B, the distraction head 206 preferably includes the first head component 206A having a proximal portion and a distal portion as well as the second head component 206B having a proximal portion and a distal portion. As shown in FIGs. 46A and 46B, the first head component 206A includes an engagement slot 222A at the proximal end. In addition, the second head component 206B includes a pass-through slot 222B which is aligned with the engagement slot 222A. The engagement slot 222A of the first head component 206A preferably receives and mounts to the distal end of the first arm 204A. The first arm 204A preferably extends through the pass-through slot 222B in the second head component 206B to allow the arm 204A to freely move the first head component 206A without interfering with the second head component 206B. The proximal portion of the second distraction head 206B is attached to the distal end of the second arm 204B. The second arm 204B is preferably mounted to the underside 240 of the second head component 206B, whereby the second arm 204B is located adjacent to the first arm 204A. It should be noted that the above description of the head components is preferred and can have any other appropriate configuration to allow distraction in accordance with the present invention.

The distal portion of both first and second distraction heads 206A, 206B includes leading edges, shown as 230A and 230B, which are used to penetrate the facet joint to insert the distraction head 206 therein The distal portion of the first and second head components, as shown in FIG. 46A, include several fingers which are shown alternately arranged. In particular, the first distraction head 206A is shown to have two fingers 224A whereas the second distraction head 206B is shown to have three fingers 224B. In another embodiment, the upper and lower distraction heads 206A, 206B have a greater or fewer number of fingers than that shown in FIG. 46 A, including only one finger each. The fingers 224 A, 224B together form an overall rounded leading edge 230 of the distraction head 206 as shown in FIG. 46B. In another embodiment, the leading edges 230 of the fingers do not form a rounded leading edge, but can form any other shape.

As shown in FIGs. 46A and 46B, the second head component 206B includes finger slots 232 which receive the fingers 224 A of the first head component 206 A when the distraction head 206 is in the non-distracted position (FIG. 46B). In the non-distracted position, as shown in FIG. 46B, the first head component 206A and the second head component 206B are co-planar, whereby the fingers 224A and 224B are preferably inter-digitated. The co-planar head components provide a height dimension or thickness which allows the distraction head 206 to be easily inserted into the facet joint. Upon the handles 202 being squeezed, the first head component 206A is forced away from the second head component 206B, thereby causing the first set of fingers 224A from sliding out of the finger slots 232 of the second head component 206B. The first head component 206A thus moves apart from the second head component 206B until the desired distance between the head components is achieved. As shown in FIG. 46A, the fingers 224A of the first head component 206 A are separated from the fingers 224B of the second head component 206B and is no longer co-planar in the distracted position. As shown in FIG. 46A, the fingers 224A, 224B each have a superior surface 226A, 226B, as well as an inferior surface 228A, 228B. In one embodiment, the leading edge 231 A, 231B of the fingers 224A, 224B are rounded or curved, as shown in FIGs. 46A and 46B. In another embodiment, the leading edges of the fingers 224A, 224B are sharpened.

In one embodiment, the superior surfaces 226A, 226B of the distraction head components 206A, 206B mate with the infeπor facet of the vertebral body when the distraction head 206 is inserted into the facet joint. Additionally, in one embodiment, the inferior surfaces 228A, 228B of the distraction heads 206 A, 206B mate with the superior facet of the vertebral body. However, it is contemplated that the tool 203 can be oriented upside down such that the superior surface of the head 206 mates with the superior facet and the inferior surface of the head 206 mates with the infeπor facet of the vertebral bodies.

As shown m FIGs. 46A and 46B, the distal portion of the distraction head 206 is relatively flat such that the supeπor and infeπor surfaces 226, 228 of the head components 206A, 206B are generally parallel with one another and have a uniform thickness. In another embodiment, the inferior and superior surfaces taper toward each other at the leading edge 231 A, 231B. The head components 306A, 306B can alternatively be shaped to contour the shapes of the facets. The facet itself is somewhat shaped like a ball and socket joint. Accordingly, as depicted in FIGs. 47 A and 47B, the distraction head 306 can have a convex superior surface 326 and a concave inferior surface 328. The curved supeπor and infeπor surfaces preferably taper toward each other at the leading edge 322A, 322B to facilitate insertion, while the remainder of the distraction head has a uniform thickness.

In addition, as shown in FIG. 47B, the individual head components each can have a concave and/or convex shape. In another embodiment, one of the supenor and infeπor surfaces 326A, 326B, 328A, 328B have a convex or concave shape, whereas the other surface is planar and does not have a curved shape. The supeπor and infeπor surfaces of the distraction head 306 thus preferably contour the respective facets of the joint. The contour of the superior and/or inferior surfaces of the head 306 allows the upper and lower head components to apply a relatively constant force to the superior and infeπor facets while the tool is actuated to the distracted position. In addition, the contoured shaped of the distraction head 306 along with its fingers allow the head components to obtain a better grip with their respective facets duπng the distraction procedure. FIGs. 48A and 48B illustrate another embodiment of the tool having the distraction head in an alternative oπentation than that shown in FIGs.44 and 45. As shown in FIG. 48A, the tool 403 includes the handle portion 402, the arm section 404 and the distraction head 406. As shown in FIG.48A, the arm portion 404 is oriented along the X-axis. However, unlike the tool 203 described in FIGs.44 and 45, the distraction head 406 extends from the arm portion 404 such that the leading edge 430 faces in the positive Z direction. In the embodiment shown in FIG.48A, the distraction head 406 extends from the arm portion along the positive Z direction at approximately a 90 degree angle with respect to the arm 404. However, the distraction head 406 can be oriented to extend from the arm 404 along the negative Z direction or at any other angle besides 90 degrees.

In operation, actuation of the handle 402A causes the arm 404A to move along the X axis to actuate the distraction head 406 as shown in FIG. 48B. As shown in FIG. 48B, the leading edges 430A and 430B of the first and second head components 406A, 406B are preferably tapered. The orientation of the leading edge 230 in the Z direction allows the tool 403 to be oriented in a different manner than the tool 203 in FIGs. 44 and 45 duπng the implantation procedure. This alternative oπentation of the tool 403 may be advantageous to distract facets along different portions of the spine which require the tool 403 to be oriented at a different angle. Additionally, the individual tastes of each physician may prefer the alternative orientation of the tool 403 over the orientation of the head 206 in the embodiment in FIGs. 44 and 45.

FIGs.49A - 49C illustrate one method of distracting adjacent facets in accordance with the tool of the present invention. FIG.49D illustrates a flow chart of the method of implantation in accordance with one embodiment of the invention The facet joint 60 is initially accessed as in step 602, as shown in FIG. 49A. A sizing tool can be inserted into the facet joint 60 to select the appropriate size of implant to be inserted as in step 604. In one embodiment, the sizing tool is a unit separate from the tool 203 of the present invention. In another embodiment, the tool 203 of the present invention has a sizing gauge to allow the surgeon to determine what size of implant is to be inserted into the facet joint as discussed in relation to FIG. 49. As shown in FIG.49A, the leading edge 231 of the tool 203 is then inserted into the entrance of the facet joint 60. The leading edge 231 of the tool 203 is then urged into the facet joint 60 until the distraction head 206 is sufficiently displaced within the facet joint 60 and between the supeπor and inferior facets 56, 58, as in FIG. 49B. In FIGs. 49A - 49C, the tool 203 accesses the joint from a supeπor approach (i.e. upside down). However, it should be noted that the tool 203 can alternatively access the facet joint from an inferior (e.g. πght side up) or lateral (e.g. sideways) approach.

Once the distraction head 206 is inserted, the physician squeezes the handles 202A, 202B together, whereby the distraction head components 206A and 206B separate from one another and distract the facet joint and surrounding tissue in order to facilitate insertion of the implant, as in step 604 (FIG.49C). Once the adjacent facets are distracted apart the desired distance, the tool 203 is then removed from the joint, thereby leaving the adjacent facets apart from one another. The distracted tissue surrounding the facets slowly contract, thereby leaving time for the physician to urge the natural or artificial facet joint spacer or inter-facet joint spacer 104 of the implant between the facets into the facet joint, as in step 606.

Once the natural or artificial joint is inserted, the lateral mass plate of the implant is pivoted downward about the hinge toward the lateral mass or to the lamina, as in step 608. Once the lateral mass plate is positioned, or pπor to the positioning of the lateral mass plate, a bore can be drilled into the bone to accommodate the bone screw. The screw is then placed through the bore and secured to the bone to anchor the natural or artificial facet joint spacer or inter-facet joint spacer in place as in step 610. In order to lock the bone screw and position of the natural or artificial facet joint spacer or inter-facet joint spacer and lateral mass plate in place, the locking plate is positioned over the lateral mass plate, as in step 612. The keel located adjacent to the locking plate can preferably self-cut a groove into the bone to lock the keel and anchor the implant, as in step 614. The locking plate is then fastened to the lateral mass plate with the screw through the bore, as in step 616. This method is then repeated for any other facet joints in the spine, as in step 618.

FIG. 5OA and 5OB illustrate another embodiment of the tool of the present invention The embodiment shown in FIGs. 5OA and 5OB includes a distraction head 806 which is configured to distract adjacent facets of the vertebral bodies and simultaneously allow insertion of the implant into the facet joint. The tool 803 shown in FIGs. 5OA and 5OB includes the handle portion 802, the arm portion 804 as well as the distraction head 806.

As shown in FIGs. 5OA and 5OB, the fingers of the distraction head 806 are offset and adjacent to the arms 804A and 804B of the tool 803. As shown in FIGs. 5OA and 5OB, the distraction head 806 includes a leading edge 808 which is shown facing the negative Y direction as well as insertion edges 811A, 811B which face the positive Y direction. The insertion edges 811A, 811B are preferably located on the opposite end of the head 806 from the leading edge 808 The leading edge 808 is configured to be inserted into the facet joint to distract the adjacent facets apart as stated above. The insertion end 81 IA, 81 IB, upon distraction, allows the implant to be inserted into the facet joint while the tool 203 is simultaneously distracting the facets apart. The insertion edges 81 IA, 81 IB of the head components 806A, 806B, respectively, move apart as the head components 806A, 806B are distracted. This creates an insertion conduit 824 between (FIG. 50B) the first and second head components 806A, 806B The insertion conduit 812 has a height distance, D, which provides adequate clearance between the inferior surface 822 of the first head component 806A and the superior surface 824 of the second head component 804B to allow the implant to be inserted therethrough. As stated above, the distraction head 806 is offset and located adjacent to the arms 804 and handle 802 of the tool 803, whereby the location of the head 806 provide ample room to insert the implant therethrough.

In operation, upon the distraction head 806 being inserted into the facet joint, the handles 802 are squeezed together to cause the distraction head components 806 to separate, thereby distracting the facets until the insertion conduit 812 is at the desired height dimension D. The desired height dimension, D, will depend on several factors, such as size of the natural or artificial inter-facet joint or inter-facet joint spacer, the thickness of the fingers of the head components, and the location of the facet joint (e.g. cervical, thoracic, lumbar). It is preferred that the height dimension D be between 1.5 and 2.5 mm, although other dimensions are contemplated. The height dimension D can be measured by a distraction gauge, as stated below, to achieve the desired height dimension. Upon achieving the desired height dimension, D, the natural or artificial insertion joint of the implant is inserted into the insertion conduit 812 via the insertion ends 811 A, 811B. Consideπng that the insertion conduit 812 is in communication with the facet joint of the spine, the implant is able to slide through the conduit 812 into the facet joint. Upon the natural or artificial mter-facet joint or inter-facet _joint spacer being secured in the facet joint, the distraction head 806 can then be removed from the facet _joint, thereby leaving the implant inserted therein. The implant can then be anchored as discussed above.

This embodiment allows the physician to maintain the distraction distance between the facets while inserting the implant. This embodiment, including the sizing gauge discussed below, can allow the physician to size, distract, and insert the implant using one tool. It should be noted that although the embodiment in FIG. 49A has the lead and insertion edges of the distraction head facing in the Y direction, the lead and insertion edges can face the Z direction or any other direction.

In one embodiment shown in FIG. 51, the distraction tool 903 can include a sizing mechanism in accordance with one embodiment of the present invention. As shown in FIG 51, the distraction gauge 950 is coupled to one of the handles 902 A and 902B. The other handle can include a flag 952 or pointer for indicating a distraction height measurement on the distraction gauge 950 Thus, as the handle 902A is urged toward the distraction position, the distraction gauge 950 slides past the flag 952, along with indicia indicating the increasing distraction height, D, between the distraction head components 906A and 906B In one embodiment, the distraction gauge 950 is configured to provide the amount of distance between the inferior surface of the first head component 906A and the superior surface of the second head component 906B (i.e. the insertion conduit). In another embodiment, the distraction gauge 950 can be configured to include the thickness of the first and second head components and thereby indicate the total distraction distance between adjacent facets.

In one embodiment, the tool 903 includes a spπng mechanism to urge the handles 902A, 902B apart toward the non-distracted position. For example, a leaf spring 912 can be configured along the inner surfaces of the handles 902 A, 902B to provide an outward bias against the handles 902 A, 902B. In another example, a spring can be positioned between the interior wall of the slot 918 and the wedge portion 916 of the arm 904A to urge the wedged portion 916 and thus the handle 902A toward the non-distracted position. Additionally, or alternatively, the tool 903 can include a locking mechanism to lock the tool 903 in a desired position. For example, the locking mechanism can include a threaded rod 914 which is coupled to one of the handles 902A, 902B at a pivot point 916, whereby the rod 914 freely passes through a through-hole in the other of the first and second handles 902A, 902B. The rod 914 includes a turning bolt 922 on the outer surface of the handle 904A which limits movement of the handles 902 which is caused by the force of the spring 910. As the handle 902A is urged closed, the threaded rod 914 passes through the through-hole and pivots to follow the arcing travel of the handle 902 A A distraction stop 920 can be positioned along the threaded rod 914 and sized such that the distraction stop 920 blocks the free travel of the threaded rod 914, thereby preventing further movement of the handle 902 and limiting the distraction height In one embodiment, the distraction stop 920 is fixed in position along the threaded rod 914, however, in other embodiments the distraction stop 920 can be adjustably positionable along the threaded rod 914 to allow the maximum distraction height to be adjusted.

MATERIALS FOR USE IN IMPLANTS OF THE PRESENT INVENTION

As alluded to above, and as descπbed in further detail as follows, in some embodiments, the implant, and components of the implant (i.e., a lateral mass plate, a bone screw, a locking screw, etc.) can be fabricated from medical grade metals such as titanium, stainless steel, cobalt chrome, and alloys thereof, or other suitable implant material having similar high strength and biocompatible properties. Additionally, the implant can be at least partially fabricated from a shape memory metal, for example Nitinol, which is a combination of titanium and nickel. Such materials are typically radiopaque, and appear during x-ray imaging, and other types of imaging. Implants in accordance with the present invention, and/or portions thereof (in particular a natural or artificial facet joint spacer or mter-facet joint spacer) can also be fabricated from somewhat flexible and/or deflectable material. In these embodiments, the implant and/or portions thereof can be fabricated in whole or in part from medical grade biocompatible polymers, copolymers, blends, and composites of polymers. A copolymer is a polymer derived from more than one species of monomer A polymer composite is a heterogeneous combination of two or more materials, wherein the constituents are not miscible, and therefore exhibit an interface between one another A polymer blend is a macroscopically homogeneous mixture of two or more different species of polymer Many polymers, copolymers, blends, and composites of polymers are radiolucent and do not appear during x-ray or other types of imaging Implants comprising such materials can provide a physician with a less obstructed view of the spine under imaging, than with an implant compπsing radiopaque materials entirely. However, the implant need not comprise any radiolucent mateπals.

One group of biocompatible polymers is the polyaryletherketone group which has several members including polyetheretherketone (PEEK), and polyetherketoneketone (PEKK). PEEK is proven as a durable material for implants, and meets the criterion of biocompatibihty. Medical grade PEEK is available from Victrex Corporation of Lancashire, Great Britain under the product name PEEK-OPTIMA. Medical grade PEKK is available from Oxford Performance Mateπals under the name OXPEKK, and also from CoorsTek under the name BioPEKK. These medical grade materials are also available as reinforced polymer resins, such reinforced resins displaying even greater material strength In an embodiment, the implant can be fabricated from PEEK 450G, which is an unfilled PEEK approved for medical implantation available from Victrex Other sources of this material include Gharda located in Panoh, India. PEEK 450G has the following approximate properties: Property Value

Density 1.3 g/cc

Rockwell M 99

Rockwell R 126

Tensile Strength97 MPa

Modulus of Elasticity 3.5 GPa

Flexural Modulus 4.1 GPa

PEEK 450G has appropriate physical and mechanical properties and is suitable for carrying and spreading a physical load between the adjacent spinous processes. The implant and/or portions thereof can be formed by extrusion, injection, compression molding and/or machining techniques.

It should be noted that the material selected can also be filled. Fillers can be added to a polymer, copolymer, polymer blend, or polymer composite to reinforce a polymeric material. Fillers are added to modify properties such as mechanical, optical, and thermal properties. For example, carbon fibers can be added to reinforce polymers mechanically to enhance strength for certain uses, such as for load bearing devices In some embodiments, other grades of PEEK are available and contemplated for use in implants in accordance with the present invention, such as 30% glass-filled or 30% carbon-filled grades, provided such mateπals are cleared for use in implantable devices by the FDA, or other regulatory body. Glass-filled PEEK reduces the expansion rate and increases the flexural modulus of PEEK relative to unfilled PEEK. The resulting product is known to be ideal for improved strength, stiffness, or stability. Carbon-filled PEEK is known to have enhanced compressive strength and stiffness, and a lower expansion rate relative to unfilled PEEK. Carbon-filled PEEK also offers wear resistance and load carrying capability

As will be appreciated, other suitable similarly biocompatible thermoplastic or thermoplastic polycondensate materials that resist fatigue, have good memory, are flexible, and/or deflectable, have very low moisture absorption, and good wear and/or abrasion resistance, can be used without departing from the scope of the invention. As mentioned, the implant can be comprised of polyetherketoneketone (PEKK). Other material that can be used include polyetherketone (PEK), polyetherketoneetherketoneketone (PEKEKK), polyetheretherketoneketone (PEEKK), and generally a polyaryletheretherketone. Further, other polyketones can be used as well as other thermoplastics. Reference to appropriate polymers that can be used in the implant can be made to the following documents, all of which are incorporated herein by reference. These documents include: PCT Publication WO 02/02158 Al, dated January 10, 2002, entitled "Bio-Compatible Polymeric Materials;" PCT Publication WO 02/00275 Al , dated January 3, 2002, entitled "Bio-Compatible Polymeric Materials;" and, PCT Publication WO 02/00270 Al , dated January 3, 2002, entitled "Bio-Compatible Polymeπc Materials." Other materials such as Bionate7, polycarbonate urethane, available from the Polymer Technology Group, Berkeley, California, may also be appropπate because of the good oxidative stability, biocompatibility, mechanical strength and abrasion resistance. Other thermoplastic materials and other high molecular weight polymers can be used. The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to practitioners skilled in this art. The embodiments were chosen and described in order to explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for vaπous embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

WHAT is CLAIMED:

1. A facet joint implant that addresses spinal stenosis and other ailments of the spine while maintaining mobility of the facet joint, the implant comprising: an anchoπng plate; a facet joint spacer; and an articulation joint connecting the anchoπng plate to the facet joint spacer.

2. The implant of claim 1 , wherein the articulation joint is one of a hinge, a ball-and-socket joint, and bendable matenal.

3. The implant of claim 1 , wherein the articulation joint includes: a cavity with the anchoring plate; and a ball-shaped end extending from the facet joint spacer and positioned in the cavity of the anchoπng plate.

4. The implant of claim 1 , further compπsing: a locking screw; a bone screw; wherein: the anchoπng plate further includes a first bore and a second bore; the bone screw is receivable within the first bore; and the locking screw is receivable within the second bore.

5. The implant of claim 4, wherein the locking screw has a head that blocks the bone screw from at least one of a backward displacement and a rotational displacement.

6. The implant of claim 4, wherein the locking screw further compπses a chisel-point end, wherein the chisel point end self-cuts the locking screw into the vertebra.

7. The implant of claim 1, wherein when said articulation joint allows said facet joint spacer is to swivel and tilt relative to the anchoring plate.

8. The implant of claim 1 wherein said facet joint spacer is shaped to accommodate and fit between superior and inferior portions of a facet joint.

9. The implant of claim 1 wherein the anchoπng plate is adapted to anchor to the lateral mass.

10 The implant of claim 1 wherein the facet joint spacer is adapted to distract the spinal facet joint and allow mobility of the spinal facet joint.

11. The implant of claim 1 including said facet joint spacer having a convex surface adapted to mate with the facet joint.

12 The implant of claim 1 wherein: the facet joint spacer includes a wedge-shaped front end adapted to allow the front end to be wedged into a facet joint, wherein the facet joint spacer distracts the facet joint and increases the foraminal area, without eliminating mobility of the facet joint.

13. A facet joint implant adapted to correct spinal stenosis and other ailments of the spine, the implant comprising: a first facet joint spacer adapted to be positioned within a first facet joint formed by two adjacent spinal vertebrae of a first level; a second facet joint spacer adapted to be positioned within a second facet joint formed by the two adjacent spinal vertebrae of the first level; and a collar joining the first facet joint spacer with the second facet joint spacer.

14 The facet joint implant as in claim 13 wherein the collar is connected flexibly with the first facet joint spacer by a first hinge and the collar is connected flexibly with the second facet joint spacer by a second hinge.

15. The facet joint implant as in claim 13 wherein the collar is connected flexibly with the first facet joint spacer and the collar is connected flexibly with the second facet joint spacer.

16. The facet joint implant as in claim 13 wherein the collar further comprises a first bore positioned adjacent to the first facet joint spacer, and a second bore positioned adjacent to the second facet joint spacer, the first bore capable of accepting a first bone screw and the second bore capable of accepting a second bone screw, adapted to secure the implant to the vertebra

17. The facet joint implant as in claim 13 wherein the collar can be bent to conform to the anatomy of a patient's cervical spine.

18. The facet joint implant as in claim 16 including a first locking device positioned to prevent the displacement of the first bone screw, and a second locking device positioned to prevent the displacement of the second bone screw.

19. The facet joint implant as in claim 13 wherein a surface of the first facet joint spacer and a surface of the second facet joint spacer are convex to approximate the shape of a cervical facet joint.

20. The facet joint implant as in claim 13 wherein a first distal end of the first facet joint spacer and a second distal end of the second facet joint spacer are tapered to facilitate insertion into a cervical facet joint.

21. The facet joint implant as in claim 1 wherein the implant is adapted to be implanted without resection of bone.

22. A facet joint implant of claim 1 comprising: a bone screw; a locking screw; the anchoπng plate receives the bone screw and the locking screw; and wherein the locking screw is adapted to self-cut into a vertebra and to block the bone screw, the locking screw and the bone screw adapted to anchor the anchoπng plate to the vertebra.

23. The implant of claim 22 wherein the locking screw has a head that blocks the bone screw from at least one of a backward displacement and a rotational displacement.

24. The implant of claim 22 wherein the locking screw further compπses a chisel-point end, wherein the chisel point end self-cuts the locking screw into the vertebra.

25. A facet joint implant of claim 1 comprising- the facet joint spacer adapted to be inserted into a facet joint, the facet joint spacer pivotable between an extended position and a folded position with respect to the anchoring plate, wherein the facet joint spacer is configured such that the facet joint spacer cannot pivot beyond the extended position

26. The implant of claim 25 wherein the facet joint spacer includes a rear protrusion to prevent movement of the facet joint spacer beyond the extended position.

27. The implant of claim 1 wherein the facet joint spacer includes a convex top surface and a bottom surface, wherein the top surface tapers toward the bottom surface at an angle to form a front edge

28. The facet joint implant of claim 1 , wherein the anchoring plate includes an engagement aperture adapted to receive a retractable engaging member of an implanting tool.

29. The implant of claim 1 wherein the anchoring plate further comprises a side surface having an protrusion adapted to correspondingly register in a receiving slot in an implanting tool

30. The implant of claim 1 wherein the anchoring plate further comprises a pair of winged protrusions along opposing side surfaces, wherein the protrusions are adapted to register in corresponding slots in an implanting tool

31. The facet joint implant of claim 1 , in combination with a tool for sizing a facet joint in order to select a facet joint implant for implanting in the facet joint, said tool comprising, a handle; an inter-facet sizer, the mter-facet sizer having a rounded distal end and a proximal end and connected with the handle at the proximal end, and a stop at the proximal end of the inter-facet sizer, the stop adapted to prevent over-insertion of the inter-facet sizer during sizing.

32 The tool as in claim 31 wherein the distal end of the inter-facet sizer is tapered in thickness to facilitate insertion into the cervical facet joint to be sized.

33 The facet joint implant of claim 31 wherein the articulation joint is narrower than the facet joint spacer.

34. The implant of claim 1 wherein the facet joint spacer and the flexible connection together are formed into a P-shape.

35. The facet joint implant of claim 1 in combination with a distraction tool to distract adjacent facets in a spine for insertion of the implant comprising: a. a distraction head having a first head component and a second head component coplanar with one another in a closed position; and b. an actuatable handle coupled to the distraction head, wherein the first head component and the second head component are non-coplanar when the handle is operated to actuate the first and second head components to an open position.

36. The tool of claim 35 wherein the first head component includes a first set of fingers and the second head component includes a second set of fingers, wherein the first and second sets of fingers are alternately configured with one another.

37. The facet joint implant of claim 1 in combination with an implanting tool to insert implant, the tool comprising: a. a handle having a switch; and b. an engaging head extending from the handle and adapted to receive the implant, the engaging head including a forked end having a pair of sidewalls adapted to receive corresponding sidewalls of the implant, the engaging head coupled to the actuating switch and configured to allow the received implant to be disengaged therefrom when the switch is actuated.

38. The tool of claim 37 wherein the engaging head further compπses an engaging member positioned between the sidewalls and movable between an extended position and a retracted position when the switch is actuated, the engaging member adapted to be inserted into an engaging aperture of the implant when in the extended position.

39. The tool of claim 37 wherein at least one of the sidewalls of the engaging head includes a slot adapted to receive a protrusion from the sidewall of the implant.

40. The facet joint implant of claim 1 including: a bone screw that is disposed through the anchoring plate and is adapted to secure the anchoring plate to the vertebra, a locking screw that holds the bone screw in place in the anchoring plate; wherein said locking screw has a first position that locks the bone screw in the anchoπng plate and a second position that allows the bone screw to be removed from the anchoring plate.

41. The implant of claim 40 wherein said locking screw has an asymmetrical head.

42. The implant of claim 41 wherein said head includes a cut-out that allows the bone screw to be removed from the anchoring plate.

43. The implant of claim 40 wherein said locking screw includes a head with a concave portion and a convex portion.

44. The implant of claim 40 wherein the bone screw is received in a recess in the anchonng plate and the locking screw is received in a recess of the anchoring plate.

45. The facet joint implant of claim 1 including at least one protrusion extending from the facet joint spacer which is adapted to retain the facet joint spacer in the facet joint.

46. The implant of claim 45 wherein: said facet joint spacer has a superior surface and an inferior surface; the superior surface is adapted to be positioned adjacent to an inferior facet of a facet joint; the inferior surface is adapted to be positioned adjacent to a superior facet of a facet joint; and the at least one protrusion extends from the infeπor surface and is adapted to engage the superior facet.

47. The implant of claim 45 wherein: a plurality of protrusions extend from the infeπor surface.

48. The implant of claim 45 wherein: the at least one protrusion points away from a direction of insertion of the facet joint spacer into a facet joint.

49. The facet joint implant of claim 1 wherein: said facet joint spacer including an inferior shim and a superior shim, wherein said infeπor shim is stiffer and less compliant that the superior shim.

50. The implant of claim 49 wherein said superior shim is molded onto said inferior shim

51. The implant of claim 49 wherein said infeπor shim is comprised of a metal and said supeπor shim is comprised of a polymer.

52. The implant of claim 49 wherein said infeπor shim consists of one of titanium and stainless steel and the supeπor shim consists of polyaryletherketone.

53. The facet joint implant of claim 49 wherein said inferior shim is comprised of a different material than the supeπor shim.

54. The implant of claim 42 wherein said cut-out is crescent shaped.