WO2012035479A2

WO2012035479A2 - Spinal fixation system and pedicle screw therefor

Info

Publication number: WO2012035479A2
Application number: PCT/IB2011/053965
Authority: WO
Inventors: Shahar Peled; Yaniv Glozman
Original assignee: Facetmed Ltd.
Priority date: 2010-09-13
Filing date: 2011-09-11
Publication date: 2012-03-22
Also published as: GB2483531A; GB201108901D0; WO2012035479A3

Abstract

A spinal fixation system and a pedicle screw therefor are disclosed. The spinal fixation system retains some degrees of movement relatively to the vertebra after the implantation, which achieves a number of clinical benefits.

Description

SPINAL FIXATION SYSTEM AND PEDICLE SCREW THEREFOR

TECHNICAL FIELD

[001 ] The present invention relates to posterior spinal fixation systems and methods. In particular, the invention relates to spinal fixation systems that retain some degrees of movement relatively to the vertebra and a pedicle screw therefor.

BACKGROUND ART

[002] It is believed that the pertinent state-of-the-art is represented by US patents Ser. Nos 4805602, 5360431 , 5129388, 6032677, 7303563, 5899905, US patent applications Ser. Nos 2005182404, 2008015585, 2009254123, 20021 1 1692, 2005283153, 2005277920, European patent applications Ser. Nos 1059066, 0407332 as well as by Chinese patents/applications Ser. Nos 2562737, 2788752, 201 1 68036, 101224133 and international publication WO2008045179.

SUMMARY OF THE INVENTION

[003] Known in the art spinal fixation systems that interconnect several vertebrae are typically affixed during their implementation, forming a rigid interconnecting backbone structure that is anchored in the vertebrae and essentially immovable relatively thereto.

[004] There are spinal fixation systems interconnecting several vertebrae while allowing some degrees of freedom in the movement of one vertebra relatively to the other, such as these disclosed in international patent application WO2005087120 entitled "PEDICLE SCREW" and US patent 6402752 entitled "POLYAXIAL PEDICLE SCREW". However neither of those systems allows a degree of freedom in the movement of the anchoring element and the vertebra itself. As will become apparent, a degree of freedom in the movement of the anchoring element and the vertebra itself entails several clinical benefits.

[005] One aspect of the invention is concerned with providing spinal fixation systems, wherein the anchoring element, henceforth referred to as pedicle screw, comprises a part that adjoins the vertebra and retains some degrees of movement relatively thereto. The movement of the part that adjoins the vertebra is characterized by that it is more of an isotropic than polyaxial type. The movements of the part that adjoins the vertebra are characterized by that they are micro- and/or vibratory movements. The micro- and/or vibratory movements, henceforth MVM, between the part of the pedicle screw that adjoins the vertebra and the facet of the vertebra disposed vis-a-vis said part facilitate a prompt ingrowth of the osseous tissue from the latter into the former. The MVM are further distribute and disperse the loads exerted onto pedicle screw and amortize the kinetic energy of the moments within the spinal fixation system.

[006] Another aspect of the invention is concerned with providing spinal fixation systems is concerned with preserving the structural integrity of the vertebral tissue into which the pedicle screw is screwed. The osseous tissue is characterized by heterogeneous density. Cortical osseous tissue is denser, whereas the trabecular or cancellous osseous tissue is relatively more porous and consequently weaker. As a result of the heterogeneous osseous density, the loads exerted onto pedicle screws are unevenly distributed between the cortical and cancellous osseous tissues. Therefore frequently the loads exerted onto pedicle screws known in the art, gradually defect the structural integrity of the cortical osseous tissue surrounding the pedicle screws; whereby the pedicle screws gradually loosening and progressively gain displacement freedom within the osseous tissue.

[007] In light of the foregoing, MVM that distribute and disperse the loads exerted onto pedicle screw and hence contribute to the deduction of loads exerted onto cortical osseous tissue. Consequently the distribution and dispersement of the the loads exerted onto pedicle screw by formation of MVM preserve the structural integrity of the cortical osseous tissue.

DEFINITION

[008] The terms: facet, vertebral facet and surface of the facet, throughout the specification and claims hereinafter, refer to a portion of the posterior surface of the vertebra, corresponding to a protection of the vertebral pedicle, into which the pedicle screws known in the art are usually screwed. The aforementioned portion of the posterior vertebral surface is colloquially referred to as upper pedicle. DESCRIPTION OF THE DRAWINGS

[009] The present invention will be understood and appreciated more comprehensively from the following detailed description taken in conjunction with the appended drawings in which:

FIG 1 A to 1 D are various views of a vertebra; FIG 2A to 2F are schematic diagrams of the vertebra adjoining part mounted onto vertebra shown in FIG 1 A to 1 D;

FIG 3A to 3F are schematic diagrams of another embodiment of vertebra adjoining part and buffering means thereof ;

FIG 4A to 4F are schematic diagrams of yet another embodiment of vertebra adjoining part and buffering means thereof;

FIG 5A to 5F are schematic diagrams of an embodiment of vertebra adjoining part comprising a mesh-like structure;

FIG 6A to 6F are schematic diagrams of an embodiment of vertebra adjoining part comprising a porous structure;

FIG 7A to 7E are schematic diagrams of yet another embodiment of vertebra adjoining part comprising a mesh-like structure;

FIG 8A to 8C are schematic diagrams of an another embodiment of vertebra adjoining part comprising a major bone screw;

FIG 9A is a posterior perspective view of an inferior portion of a human spine;

FIG 9B is an enlarged view of the inferior portion of a human spine shown in FIG. 9A, incorporating a exemplar spinal fixation assembly;

FIG. 9C is an isometric view of the exemplar spinal fixation assembly, shown in FIG. 9A;

FIG. 10A is an isometric exploded view of an embodiment of a pedicle screw;

FIG. 10B is a side view of the pedicle screw shown in FIG. 10A;

FIG. 10C is a cross-sectional view of the pedicle screw shown in FIG. 10B;

FIG. 10D is a top view of the pedicle screw shown in FIG. 10A;

FIG. 10E is a bottom view of the pedicle screw shown in FIG. 10A;

FIG. 10F is an enlarged view of the cross-section shown in FIG. 10C;

FIG. 11 A is an isometric view of another embodiment of a pedicle screw;

FIG. 11 B is an isometric exploded view of an embodiment of a bone anchoring plate;

FIG. 11C to 11 E are respectively a side, front and top views of an assembly of the pedicle screw shown in FIG. 11 A and the bone anchoring plate shown in FIG. 11 B, depicting various degrees of freedom in movements of the former relatively to the latter; FIG. 11 F to 111 are respectively a side, isometric, isometric exploded and side exploded views a bone screw and buffering means therefor.

[010] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown merely by way of example in the drawings. The drawings are not necessarily complete and components are not inevitably to scale; emphasis instead being placed upon clearly illustrating the principles underlying the present invention.

DISCLOSURE OF THE INVENTION

[01 1 ] Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with technology- or business-related constraints, which may vary from one implementation to another. Moreover, it will be appreciated that the effort of such a development might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[012] In accordance with some embodiments of the present invention, reference is now made to Figs 1A to 2F, which respectively are schematic diagrams of vertebra adjoining part 20, hereinafter VAP, mounted onto curvilinear facet of vertebra 10 and views of VAP 20. VAP 20 comprises a mesh-like saddle 22, the structured anterior face of which is adapted to posteriorly conform to the curvilinear facet of vertebra 10, essentially as shown in Figs 1A to 1 D.

[013] The mesh of saddle 22 is of a hexagonal lattice shape; wherein merely the structured butt-ends of the hexagonal lattice adjoin the curvilinear facet of vertebra 10, hence reducing the contact area between the former and the latter. A reduced contact area between the structured butt-ends of the hexagonal lattice of saddle 22 and the curvilinear facet of vertebra 10 forms an enhanced pressure on the latter and micro- penetration of the former thereto, thereby facilitating a proliferation of the vertebral osseous tissue; whereas hexagonally shaped apertures 23 providing for an ingrowth of the osseous tissue of vertebra 10 into saddle 22.

[014] VAP 20 comprises integral stem 24, extending form structured saddle 22, essentially in the posterior direction. Stem 24 is typically of a cylindrical form. Stem 24 is adapted to be operationally connected to backbone forming part s (not shown), thereinafter BFP/s, interconnecting two or more VAPs.

[015] VAP 20 further comprises screw housings 26, defining apertures 25 therein.

Screw housings 26 are oriented substantially towards the interior of the pedicle portion of vertebra 10. Screw housings 26 are adapted to accommodate pedicle screws (not shown), which are screwed into the interior of the pedicle portion of vertebra 10, thus urging the structured anterior face of saddle 22 vis-a-vis the curvilinear facet of vertebra 10 and tightening VAP 20 thereto.

[016] Screw housings 26 are furnished with buffering means, aimed at conferring to the MVM formed as a result of various forcers exerted onto stem 24 a more isotropic character; thereby dispersing the kinetic energy of the MVM across the structured anterior face of saddle 22 and the curvilinear facet of vertebra 10. The buffering means is disposed in-between the cap of pedicle screws (not shown) and screw housings 26; thereby providing for a degree of freedom in an axial displacement of pedicle screws (not shown) within screw housings 26. Exemplary buffering means furnishing screw housings 26 of VAP 20 are split-washer elements 27, disposed essentially at the top of housings 26.

[017] To depict another embodiment of the buffering means is disposed in the screw housings, reference is now made to Figs 3A to 3F, which are schematic diagrams of VAP 30 and buffering means 37 thereof. VAP 30 is essentially similar to VAP 20 shown in Figs 2A to 2F.

[018] VAP 30 comprises screw housings 36. Screw housings 36 are furnished with buffering means 37. Buffering means 37 are spacer elements formed by a plurality of somewhat bendable ribs in-between screw the interior cylindrical surface of housings 36 the and the exterior surface of pedicle screws (not shown) inserted therein; thereby providing for a degree of freedom in a lateral displacement of pedicle screws (not shown) relatively to screw housings 36 of VAP 30.

[019] To depict another embodiment of the buffering means is disposed in the screw housings, reference is now made to Figs 4A to 4F, which are schematic diagrams of VAP 40 and buffering means 47 thereof. VAP 40 is essentially similar to VAP 20 shown in Figs 2A to 2F.

[020] VAP 40 comprises screw housings 46. Screw housings 46 are furnished with buffering means 47. Buffering means 47 are bushing-like elements. Buffering means 47 are disposed in-between and along the interior cylindrical surface of screw housings 46 and the exterior surface of pedicle screws (not shown) inserted therein; thereby providing for degrees of freedom in axial and lateral displacement of pedicle screws (not shown) relatively to screw housings 46 of VAP 40.

[021 ] Some examples of bushing-like elements 47 include hollow cylindrical elements, made of a somewhat more resilient material than standard metals. Other examples of bushing-like elements 47 include heliacally wound coils, forming an essentially cylindrical firm structure.

[022] In accordance with some embodiments of the present invention, reference is now made to Figs 5A to 5F, which are schematic diagrams of VAP 50. VAP 50 comprises a mesh-like saddle 52 of a hexagonal lattice shape; essentially similar to saddle 22 of VAP 20 shown in Figs 2A to 2F. Terminal anterior portions of the hexagonal lattice structure of saddle 52 comprise pointed ridges 53 concluding with sharpened edges 54. Sharpened edges 54 of pointed ridges 53 form an enhanced pressure on the curvilinear facet of the vertebra and forcefully penetrate thereto, thereby facilitating an enhanced proliferation of the vertebral osseous tissue; whereas hexagonally shaped apertures providing for an ingrowth of the osseous tissue into the saddle of VAP 50.

[023] Integral stem 55 of VAP 50 is furnished with screw threading 56 for operational connection to one or more BFP/s, interconnecting VAP 50 and other VAP/s.

[024] In accordance with some embodiments of the present invention, reference is now made to Figs 6A to 6F, which are schematic diagrams of VAP 60. VAP 60 comprises porous saddle 62, which includes a plurality of essentially paralleling bores 63. The structured anterior face of porous saddle 62 is adapted to posteriorly conform to the curvilinear facet of the vertebra, essentially as shown in Figs 1 A to 1 D.

[025] Fortification ribs 64 interconnect stem 65 and screw housings 66.

Fortification ribs 64 are typically integrally embodied with stem 65 and screw housings 66. Fortification ribs 64 integrally embodied in saddle 62 or connected thereto, for instance by welding. Fortification ribs 64 are used to achieve a more homogenous distribution of forces exerted onto stem 65 across the entire structure of saddle 62; thereby preventing a breakage or buckling of saddle 62.

[026] Screw housings 66 of VAP 60 can be furnished with buffering means (not shown), aimed at conferring to the MVM formed as a result of various forcers exerted onto stem 65 a more isotropic character; thereby dispersing the kinetic energy of the MVM across the structured anterior face of saddle 62 and the curvilinear facet of the vertebra, similarly to the buffering means of other VAPs elaborated supra. [027] The structure of saddle 62 includes a plurality of essentially paralleling bores

63; wherein merely the portions of the structure of saddle 62 between bores 63 adjoin the curvilinear facet of hence vertebra, hence reducing the contact area between the former and the latter; whereas the lumens of bores 63 providing for an ingrowth of the osseous tissue of the vertebra into saddle 62. Moreover the plurality of essentially paralleling bores 63 terminating across the anterior structured face of saddle 62 form a plurality of pointed ridges 67 concluding with sharpened edges 68, which form an enhanced pressure on the curvilinear facet of the vertebra and forcefully penetrate thereto, thereby facilitating an enhanced proliferation of the vertebral osseous tissue.

[028] In accordance with some embodiments of the present invention, reference is now made to Figs 7A to 7E, which are schematic diagrams of VAP 70. VAP 70 comprises a mesh-like saddle 72 of a hexagonal lattice shape; essentially similar to saddle 22 of VAP 20 shown in Figs 2A to 2F. Integral stem 75 of VAP 70 is furnished with screw threading 76 for operational connection to one or more BFP/s, interconnecting VAP 70 and other VAP/s.

[029] VAP 70 is characterized by grating 74 embedded within the structure of saddle 72. Grating 74 providing for an enhanced adhesion of the osseous tissue ingrowing from the vertebra into saddle 72.

[030] In accordance with some embodiments of the present invention, reference is now made to Figs 8A to 8E, which are schematic diagrams of VAP 80. VAP 80 comprises mesh-like saddle 82 of a hexagonal lattice shape; essentially similar to saddle 22 of VAP 20 shown in Figs 2A to 2F. VAP 80 comprises modular stem 85, inserted into an aperture within the structure of saddle 82. Modular stem 85 of VAP 80 dually serves the purposes of pedicle screw and a stem of VAP 80 for an assembly of the spinal fixation system. Modular stem 85 is therefore furnished with two types of screw threadings. The anterior portion of modular stem 85, terminating with pointed tip 86, is furnished with screw threading 87, adapted for screwing stem 85 into to the osseous tissue of the pedicle of the vertebra.

[031 ] The posterior portion of modular stem 85 is furnished with screw threading 88, whereas the interior surface of the aperture within the structure of saddle 82, which modular stem 85 is inserted to, is furnished with a respectively matching screw threading (not shown); whereby stem 85 can be screwed into the structure of saddle 82. The posterior face of stem 85 comprises polygonal recess 89, adapted for operationally connecting a screw-driving tool (not shown) thereto. [032] The part of screw threading 88 of the terminal posterior portion of modular stem 85 extending from the structure of saddle 82, is adapted for operational connection to one or more BFP/s, interconnecting VAP 80 and other VAP/s.

[033] VAP 80 further comprises minor pedicle screws or pins 83, disposed within the respective structure of saddle 82, essentially coaxially to modular stem 85.

[034] Saddle 82 is typically placed onto the curvilinear facet of the vertebra and modular stem 85 is then screwed therethrough into the pedicle of the vertebra, substantially coaxially to the longitudinal centerline thereof. The pitch of screw threading 87, furnishing the anterior portion of modular stem 85, is somewhat larger than that of screw threading 88 furnishing of the posterior portion of modular stem 85; whereby upon a concomitant engagement, respectively, of screw threading 87 and screw threading 88 with the osseous tissue of the vertebra and the matching screw threading within the aperture (not shown) in saddle 82, and rotation of stem 85 by operational connecting of a screw driving tool (not shown) to polygonal recess 89, saddle 82 is forcefully tightened to the vertebra. Saddle 82 is prior and/or subsequently to that is affixed by minor pedicle screws or pins 83, screwed the osseous tissue of the vertebra thus further tightening saddle 82 to the vertebra.

BEST MODE FOR PRACTICING AND CARRYING OUT THE INVENTION

[035] In accordance with some preferred embodiments of the present invention, reference is now made to FIG 9A to 9C, showing an inferior portion of exemplar human spine 200. The inferior portion of spine 200 comprises lumbar vertebrae L1 to L5, defining the lumbar curve spine 200. Os sacrum OS is disposed inferiorly to vertebra L5 and terminates with Coccyx CO. Lumbar vertebrae L1 to L5 are interspaced by intervertebral discs D12, D23, D34, and D34, respectively; whereas disc D05 interspaces between vertebra L5 and Os sacrum OS. Exemplary assemblies 201 A and 201 B are anchored within vertebrae L4 and L5 to partially sustain the loads exerted onto intervertebral disc D45 and disperse the kinetic energy of the movements between vertebrae L4 and L5 by amortization thereof to MVM; thereby compensating for a performance of defected intervertebral disc D45.

[036] Exemplary assembly 201 comprises vertebra adjoining pedicle screw

(henceforth VAPSSS) 205, VAPSS 300 and backbone forming part (thereinafter BFP) 400, interbridging between VAPSS 205 and VAPS 300. VAPS 205 comprises bone screw 210 and polyaxial head 250. Bone screw 210 of VAPS 205 is screwed into to the osseous tissue of vertebral pedicle, substantially coaxially to the longitudinal centerline thereof. Consequently polyaxial head 250 of VAPS 205 is urged vis-a-vis a facet of the vertebra.

[037] BFP 400 is inserted into arcuate recess at the posterior portion of polyaxial head 250. BFP 400 is tightened within the arcuate recess at the posterior portion of polyaxial head 250 by bolt 405, forming interbridging structure between VAPS 205 and VAPS 300.

[038] Bone anchoring plate 450 is fastened into exterior circumferential groove of polyaxial head 350 of VAPS 300 and tightened to the vertebra by screw 470, forming a modular structure characterized by at least two potential degrees of freedom in the movements of various parts thereof relatively to VAPS 300 and capable of further amortization and dispersing of kinetic energy and/or forces exerted onto VAPS 300; thereby forming MVM and facilitating a prompt ingrowth of the osseous tissue into plate 450.

[039] Reference is now made to FIG 10A to 10F, wherein in accordance with some embodiments of the present invention, VAPS 205 is shown. VAPS 205 comprises bone screw 210, terminating with pointed anterior tip 211 and furnished with screw threading 212, adapted for screwing screw 210 into to the osseous tissue of vertebral pedicle, substantially coaxially to the longitudinal centerline thereof. The posterior of bone screw 210 of VAPS 205 comprises terminal spherical head 214, having polygonal recess 216 therein, adapted for operationally connecting a screw driving tool (not shown) thereto.

[040] VAPS 205 further comprises top crown element 220 and lateral crown elements 222. Top crown element 220 and lateral crown elements 222 for an assembly of an essentially spherical shell shape. A plurality of structured explode lines across the spherical shell assembly are formed at the interfaces between crown elements 220 and elements 222 and/or between lateral crown elements 222.

[041] The spherical shell assembly of top crown element 220 and lateral crown elements 222 is adapted to contiguously engage posterior spherical head 214 of bone screw 210, in a spherical joint-like manner; thereby forming a first articulation movement between terminal spherical head 214 of bone screw 210 and crown and crown elements 220 and 222. Lateral crown elements 222 comprise bone adjoining portions 224 that are furnished with a plurality of bores and/or knurling 226, providing for an ingrowth of the osseous tissue of the vertebra into portions 224 of lateral crown elements 222. Bone adjoining portions 224 of lateral crown elements 222 are circumferentially confined by annular member 230. [042] The aforementioned first articulation movement between terminal spherical head 214 of bone screw 210 and crown elements 220 and 222, inter alia, contributes to a positioning of bone adjoining portions 224 of lateral crown elements 222 and annular member 230 vis-a-vis the vertebra, urged towards the surface of the facet thereof.

[043] Portions 224 of lateral crown elements 222 and annular member 230 as well as any other bone facing and/or adjoining members or parts of the spinal fixation system of the invention can be covered or otherwise furnished with hydroxylapatite Ca5(P04)3(OH), to promote proliferation and adhesion of the osseous tissue.

[044] The anterior portion of polyaxial head 250 of VAPS 205 is adapted to accommodate the spherical assembly of crown elements 220 and 222, in a joint-like manner; thereby forming a second articulation movement between polyaxial head 250 and crown elements 220 and 222. The posterior portion of polyaxial head 250 of VAPS 205 comprises screw threading 252 and arcuate recess 254, adapted for operational connection to one or more BFP/s, interconnecting VAPS 205 with other VAPS/s.

[045] The assembly of VAPS 205 is held by annular tab 260 that is secured by spring washer 262. Annular tab 260 holds the spherical assembly of crown elements 220 and 222 within the anterior portion of polyaxial head 250; whereas spring washer 262 inserted into circumferential groove 264 within annular tab 260 is disposed within anterior polyaxial head 250, thereby securing assembly of VAPS 205.

[046] Upon screwing bone screw 210 of VAPS 205 into to the osseous tissue of vertebral pedicle, bone adjoining portions 224 of lateral crown elements 222 are urged towards the facet of the vertebra; whereby the aforementioned first articulation movement between terminal spherical head 214 of bone screw 210 and crown and crown elements 220 and 222 allows bone adjoining portions 224 to assume the right position vis-a-vis the vertebral tissue, providing inter alia for the formation of MVM therebetween.

[047] The aforementioned second articulation movement between polyaxial head

250 and crown elements 220 and 222 facilitates a more resilient connection between VAPS 205 and a BFP (not shown), which interconnects VAPS 205 with other VAPS (not shown), providing inter alia for the formation of MVM in the spinal fixation system of the invention. The aforementioned second articulation movement additionally provides for attaining a desired position and/or orientation of polyaxial head 250 of VAPS 205, for the installation of the BFP (not shown), prior to the final tightening of VAPS 205 to the vertebra, during the implantation at the surgery room. [048] In some preferred embodiments annular tab 260 comprises a prominent top portion. In such embodiments, upon inserting a BFP into arcuate recess 254 of polyaxial head 250 and tightening thereof therein by a bolt screwed about screw threading 252, a force is exerted by the bottom portion of the BFP onto the prominent top portion of annular tab 260; whereby annular tab 260 is forcefully urges top crown element 220 downwardly. Consequently the top crown element 220 pushes lateral crown elements 222; thereby distorting the spherical arrangement of crown elements 220 and 222 and contributing to the exploding of the spherical assembly thereof about the structured explode lines formed at the interfaces between crown elements 220 and elements 222 and/or between lateral crown elements 222. The aforementioned distorting of the spherical arrangement of crown elements 220 and 222 and exploding of the spherical assembly thereof about the structured explode lines substantially hampers the aforesaid second articulation movement between polyaxial head 250 and crown elements 220 and 222; whereby the kinetic energy and/or loads associated with VAPS 205 are essentially conveyed for the formation of MVM by the aforesaid first articulation movement between terminal spherical head 214 of bone screw 210 and crown elements 220 and 222. Accordingly, upon tightening the BFP within arcuate recess 254 of polyaxial head 250 by a bolt, the majority of kinetic energy and/or loads associated with VAPS 205 are thereafter dispersed as MVM formed between the bone adjoining portions 224 of lateral crown elements 222 and annular member 230 and the surface of the facet of the vertebra.

[049] In some yet further preferred embodiments annular tab 260 and top crown element 220 comprise an interlocking structural arrangement, such as respective ridge and grove, which interlock and thereby preclude the movement annular tab 260 and top crown element 220 relatively to each other. The preclusion of the movement annular tab 260 and top crown element 220 relatively to each diminishes the aforesaid second articulation movement between polyaxial head 250 and crown elements 220 and 222, upon tightening the BFP within arcuate recess 254 of polyaxial head 250 by a bolt; thereby conveying essentially all the kinetic energy and/or loads associated with VAPS 205 to be dispersed as MVM between the bone adjoining portions 224 of lateral crown elements 222 and annular member 230 and the surface of the facet of the vertebra.

[050] Reference is now made to FIGS 11 A to 111, wherein in accordance with some embodiments of the present invention, VAPS 300, bone anchoring plate 450 and screw 470 are shown. Polyaxial head 350 of VAPS 300 comprises exterior circumferential groove 356, used for mounting anchoring plate 450, as will be elaborated infra. [051 ] Bone anchoring plate 450 comprises platform 452, pin 454 and yoke 456.

Bone facing surfaces of platform 452 are furnished with a plurality of bores and/or knurling 453, providing for an ingrowth of the osseous tissue of the vertebra into plate 450. Bone anchoring plate 450 comprises oval aperture 455, adapted to receive minor pedicle screw 470, screwed into the osseous tissue of the vertebra thus tightening anchoring plate 450 thereto. Platform 452 further includes apertures 462, adapted to receive pin 454 therein.

[052] Yoke 456 terminates with frusto-bulb-shaped element 458 and comprises aperture 460. Pin 454 comprises screw threading 459, for securing pin 454 within apertures 460 of platform 452. Bone anchoring plate 450 is fastened into exterior circumferential groove 356 of polyaxial head 350, by positioning the frustomed faces of bulb-shaped element 458 essentially in parallel to the circumferential ridges of groove 356 and rotating plate 450 in about 90 degrees.

[053] Frusto-bulb-shaped element 458 of yoke 456 of anchoring plate 450 is slidable along the circumferential ridges of groove 356 of polyaxial head 350 rendering platform 450 capable to assume various angular positions in the directions indicated by arrows 394, 396 and 398, whereas platform 452 is pivotally rotatable relatively to yoke 456 in the directions indicated by arrows 399.

[054] Minor bone screw 470 terminates with pointed anterior tip 471 and is furnished with screw threading 472, adapted for screwing screw 470 into to the osseous tissue of vertebra. The posterior face of having screw 470 comprises polygonal recess 476, adapted for operationally connecting a screw driving tool (not shown) thereto.

[055] Bone screw 470 comprises circumferential groove 474, adapted to accommodate buffering means 480. Buffering means 480 is an annular element comprising slanted slot 482. Bone anchoring plate 450 is fastened into exterior circumferential groove 356 of polyaxial head 350 and screwed to the vertebra by screw 470, forming a modular structure characterized by at least two potential degrees of freedom in angulations of the former relatively to the latter; capable of amortization and dispersing of kinetic energy and/or forces exerted onto VAPS 350, thereby forming MVM and facilitating a prompt ingrowth of the osseous tissue.

[056] It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims which follow:

Claims

1 . A posterior spinal fixation system, comprising :

[a] at least one backbone forming part;

[b] at least two vertebra adjoining pedicle screws, said pedicle screws comprising:

[1 ] a bone screw, said bone screw comprises:

[i] a screw threading, adapted for screwing screw into the osseous tissue of vertebral pedicle;

[ii] a pointed anterior tip;

[iii] a posterior spherical head, having a recess therein, adapted for operationally connecting a driving tool thereto;

[2] at least one crown element, said at least one crown element is adapted to contiguously engage said posterior spherical head of said bone screw, in a spherical joint-like manner;

[3] a polyaxial head, said polyaxial head comprises:

[i] an anterior portion, said anterior portion is adapted to accommodate said at least one crown element, in a joint-like manner;

[ii] a posterior portion, said posterior portion comprises a recess adapted to accommodate said backbone forming part, said recess comprises a screw threading for tightening said backbone forming part therein by a bolt;

[4] an annular tab, said annular tab holds said at least one crown element within said anterior portion of said polyaxial head;

said system is characterized by:

[c] a first articulation movement formed between said spherical head of said bone screw and said at least one crown element;

[d] a second articulation movement formed between said polyaxial head and said at least one crown element.

2. The posterior spinal fixation system as in claim 1 , wherein said pedicle screws further comprising a spring washer inserted into circumferential groove within said annular tab and disposed within polyaxial head, thereby securing assembly of said pedicle screws.

3. The posterior spinal fixation system as in claim 1 , wherein said annular tab is affixable within said polyaxial head.

4. The posterior spinal fixation system as in claim 1 , wherein said crown is an assembly of an essentially spherical shell shape, comprising a plurality of individual elements, said elements form structured explode lines across said spherical shell.

5. The posterior spinal fixation system as in claim 1 , wherein said crown comprises a top element and approximately four lateral elements, forming an assembly of an essentially spherical shell shape, wherein a plurality of structured explode lines are across said spherical shell, at the interfaces between said top element and/or said lateral elements.

6. The posterior spinal fixation system as in any one of the claims 1 , 4 or 5, wherein said crown or crown elements comprise/s bone adjoining portion/s.

7. The posterior spinal fixation system as in any one of the claims 1 to 6, wherein said pedicle screws further comprising an annular member circumferentially confining said bone adjoining portions of said crown.

8. The posterior spinal fixation system as in any one of the claims 6 or 7, wherein any surface to adjoin a vertebral tissue, selected from group consisting of: a surface of said bone adjoining portions and a surface of said bone adjoining portions, are furnished with a plurality of bores and/or knurling, allowing an ingrowth of the osseous tissue thereto.

9. The posterior spinal fixation system as in any one of the claims 1 to 8, wherein any surface that adjoins the vertebral tissue is furnished with hydroxyl apatite Ca₅(P0₄)₃(OH), to promote proliferation and adhesion of the osseous tissue.

10. The posterior spinal fixation system as in any one of the claims 1 to 9, wherein upon screwing said bone screw into the osseous tissue of vertebral pedicle, said bone adjoining portion/s of said crown is/are urged towards the facet of the vertebra.

1 1 . The posterior spinal fixation system as in any one of the claims 1 to 10, wherein said first articulation movement between said terminal spherical head of said bone screw and said crown and allows said bone adjoining portions to assume a position vis-a-vis the vertebral tissue.

12. The posterior spinal fixation system as in any one of the claims 1 to 1 1 , wherein said first articulation movement between said terminal spherical head of said bone screw and said crown contributes for the formation of micro- and/or vibratory movements between said bone adjoining portions and a facet of the vertebral tissue.

13. The posterior spinal fixation system as in any one of the claims 1 to 12, wherein said second articulation movement between said polyaxial head and said crown facilitates attaining a desired position and/or orientation of said polyaxial head for the installation of said BFP.

14. The posterior spinal fixation system as in any one of the claims 1 to 13, wherein said annular tab comprises a prominent top portion.

15. The posterior spinal fixation system as in any one of the claims 1 to 14, wherein upon tightening of said BFP within said arcuate recess of said polyaxial head by said bolt, said annular tab is forcefully urged against said crown.

16. The posterior spinal fixation system as in any one of the claims 1 to 15, wherein upon tightening of said BFP within said arcuate recess of said polyaxial head by said bolt, siad top crown element pushes said lateral crown elements; thereby distorting the spherical arrangement of said crown elements and contributing to the exploding of the spherical assembly thereof about said structured explode lines.

17. The posterior spinal fixation system as in any one of the claims 1 to 16, wherein said second articulation movement between said polyaxial head and said crown is controllably hamperable upon tightening of said BFP within said arcuate recess of said polyaxial head by said bolt.

18. The posterior spinal fixation system as in any one of the claims 1 to 17, wherein upon tightening of said BFP within said arcuate recess of said polyaxial head by said bolt, the majority of kinetic energy and/or loads associated with said vertebra adjoining pedicle screws are dispersed as micro- and/or vibratory movements between said bone adjoining portions and a facet of the vertebral tissue.

19. The posterior spinal fixation system as in any one of the claims 1 to 18, wherein said annular tab and said crown comprise an interlocking structural arrangement, which precludes the movement of said annular tab relatively to said crown.

20. The posterior spinal fixation system as in any one of the claims 1 to 19, wherein said second articulation movement between said polyaxial head and said crown is controllably precluded upon tightening of said BFP within said arcuate recess of said polyaxial head by said bolt.

21 . The posterior spinal fixation system as in any one of the claims 1 to 1 9, further comprising a modular bone anchoring plate.

22. The posterior spinal fixation system as in any one of the claims 1 to 21 , further comprising a platform, pin and yoke.

23. The posterior spinal fixation system as in any one of the claims 21 or 22, wherein any surface to adjoin a vertebral tissue is furnished with a plurality of bores and/or knurling, allowing an ingrowth of the osseous tissue thereto.

24. The posterior spinal fixation system as in any one of the claims 21 to 23, wherein any surface that adjoins the vertebral tissue is furnished with hydroxylapatite Ca₅(P0₄)₃(OH), to promote proliferation and adhesion of the osseous tissue.

25. The posterior spinal fixation system as in any one of the claims 21 to 24, wherein said one anchoring plate comprises oval aperture, adapted to receive minor pedicle screw.

26. The posterior spinal fixation system as in any one of the claims 21 to 25, further comprising a minor pedicle screw adapted to be screwed into the osseous tissue of the vertebra thus tightening anchoring plate thereto.

27. The posterior spinal fixation system as in any one of the claims 21 to 26, wherein said yoke terminates with frusto-bulb-shaped element.

28. The posterior spinal fixation system as in any one of the claims 21 to 27, further comprising a vertebra adjoining pedicle screw, said pedicle screw comprises a polyaxial head characterized by an exterior circumferential groove therein.

29. The posterior spinal fixation system as in any one of the claims 21 to 28, wherein said bone anchoring plate is fastenable within said exterior circumferential groove of said polyaxial head.

30. The posterior spinal fixation system as in any one of the claims 21 to 29, wherein said minor pedicle screw is further furnished with a buffering means.

31 . The posterior spinal fixation system as in claim 30, wherein said buffering means is an annular element comprising slanted slot.

32. A vertebra adjoining pedicle screw 205 for a posterior spinal fixation system, comprising :

[a] a bone screw 210, said bone screw 210 comprising:

[1 ] a screw threading 212, adapted for screwing said bone screw 210 into the osseous tissue of vertebral pedicle;

[2] a pointed anterior tip 21 1 ;

[3] a posterior spherical head 214, having a recess 216 therein, adapted for operationally connecting a driving tool thereto;

[4] at least one crown element, said at least one crown element is adapted to contiguously engage said posterior spherical head 214 of said bone screw 210, in a spherical joint-like manner;

[b] a polyaxial head 250, said polyaxial head 250 comprises:

[1 ] an anterior portion, said anterior portion is adapted to accommodate said at least one crown element, in a joint-like manner;

[2] a posterior portion, said posterior portion comprises a recess 254 adapted to accommodate said backbone forming part, said recess 254 comprises a screw threading 252 for tightening said backbone forming part therein by a bolt 405;

[3] an annular tab 260, said annular tab 260 holds said at least one crown element within said anterior portion of said polyaxial head 250;

said vertebra adjoining pedicle screw 205 is characterized by:

[c] a first articulation movement formed between said spherical head 214 of said bone screw 210 and said at least one crown element;

[d] a second articulation movement formed between said polyaxial head 250 and said at least one crown element.

33. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said pedicle screws further comprising a spring washer 262 inserted into circumferential groove 264 within said annular tab 260 and disposed within polyaxial head 250, thereby securing assembly of said pedicle screws 205.

34. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said annular tab 260 is affixable within said polyaxial head 250.

35. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said crown is an assembly of an essentially spherical shell shape, comprising a plurality of individual elements, said elements form structured explode lines across said spherical shell.

36. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said crown comprises a top element 220 and approximately four lateral elements 222, forming an assembly of an essentially spherical shell shape, wherein a plurality of structured explode lines are across said spherical shell, at the interfaces between said top element 220 and/or said lateral elements 222.

37. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said crown or crown elements comprise/s bone adjoining portion/s 224.

38. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said pedicle screws further comprising an annular member 230 circumferentially confining said bone adjoining portions 224 of said crown.

39. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein any surface to adjoin a vertebral tissue, selected from group consisting of: a surface of said bone adjoining portions 224 and a surface of said bone adjoining portions 224, are furnished with a plurality of bores and/or knurling 226, allowing an ingrowth of the osseous tissue thereto.

40. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein any surface that adjoins the vertebral tissue is furnished with hydroxylapatite Ca₅(P0₄)₃(OH), to promote proliferation and adhesion of the osseous tissue.

41 . The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein upon screwing said bone screw 210 into the osseous tissue of vertebral pedicle, said bone adjoining portion/s 224 of said crown is/are urged towards the facet of the vertebra.

42. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said first articulation movement between said terminal spherical head 214 of said bone screw 21 0 and said crown and allows said bone adjoining portions 224 to assume a position vis-a-vis the vertebral tissue.

43. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said first articulation movement between said terminal spherical head 214 of said bone screw 210 and said crown contributes for the formation of micro- and/or vibratory movements between said bone adjoining portions 224 and a facet of the vertebral tissue.

44. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, said second articulation movement between said polyaxial head 250 and said crown facilitates attaining a desired position and/or orientation of said polyaxial head 250 for the installation of said BFP.

45. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said annular tab 260 comprises a prominent top portion.

46. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein upon tightening of said BFP within said arcuate recess 254 of said polyaxial head 250 by said bolt, said annular tab 260 is forcefully urged against siad crown

47. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein upon tightening of said BFP within said arcuate recess 254 of said polyaxial head 250 by said bolt, siad top crown element 220 pushes said lateral crown elements 222; thereby distorting the spherical arrangement of said crown elements 220 and 222 and contributing to the exploding of the spherical assembly thereof about said structured explode lines.

48. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said second articulation movement between said polyaxial head 250 and said crown is controllably hamperable upon tightening of said BFP within said arcuate recess 254 of said polyaxial head 250 by said bolt.

49. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein upon tightening of said BFP within said arcuate recess 254 of said polyaxial head 250 by said bolt, the majority of kinetic energy and/or loads associated with said vertebra adjoining pedicle screws 205 are dispersed as micro- and/or vibratory movements between said bone adjoining portions 224 and a facet of the vertebral tissue.

50. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said annular tab 260 and said crown comprise an interlocking structural arrangement, which precludes the movement of said annular tab 260 relatively to said crown.

51 . The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said second articulation movement between said polyaxial head 250 and said crown is controllably precluded upon tightening of said BFP within said arcuate recess 254 of said polyaxial head 250 by said bolt.

52. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, further comprising a modular bone anchoring plate 450.

53. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, further comprising a platform 452, pin 454 and yoke 456.

54. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein any surface to adjoin a vertebral tissue is furnished with a plurality of bores and/or knurling 453, allowing an ingrowth of the osseous tissue thereto.

55. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein any surface that adjoins the vertebral tissue is furnished with hydroxylapatite Ca₅(P0₄)₃(OH), to promote proliferation and adhesion of the osseous tissue.

56. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said one anchoring plate 450 comprises oval aperture 455, adapted to receive minor pedicle screw 470.

57. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, further comprising a minor pedicle screw 470 adapted to be screwed into the osseous tissue of the vertebra thus tightening anchoring plate 450 thereto.

58. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said yoke 456 terminates with frusto-bulb-shaped element 458.

59. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, further comprising a vertebra adjoining pedicle screw 300, said pedicle screw 300 comprises a polyaxial head 350 characterized by an exterior circumferential groove 356 therein.

60. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said bone anchoring plate 450 is fastenable within said exterior circumferential groove 356 of said polyaxial head 350.

61 . The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said minor pedicle screw 470 is further furnished with a buffering means 480.

62. The vertebra adjoining pedicle screw as in any one of the claims 32 to 62, wherein said buffering means 480 is an annular element comprising slanted slot 482.