Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B17/00—Surgical instruments, devices or methods
  • A61B17/56—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor
  • A61B17/58—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor for osteosynthesis, e.g. bone plates, screws or setting implements
  • A61B17/68—Internal fixation devices, including fasteners and spinal fixators, even if a part thereof projects from the skin
  • A61B17/70—Spinal positioners or stabilisers, e.g. stabilisers comprising fluid filler in an implant
  • A61B17/7001—Screws or hooks combined with longitudinal elements which do not contact vertebrae
  • A61B17/7041—Screws or hooks combined with longitudinal elements which do not contact vertebrae with single longitudinal rod offset laterally from single row of screws or hooks

Definitions

• the present invention concerns spinal fixation systems, and particularly system utilizing elongated rods adjacent the spinous process providing a base for connecting fixation elements to several vertebral levels. More specifically, the invention concerns improvements to the manner in which the vertebral fixation elements, such as spinal hooks and bone screws, are engaged to the elongated spinal rod.
• a bendable rod is longitudinally disposed adjacent the vertebral column, or spinous process, and is fixed to various vertebrae along the length of the column by way of a number of fixation elements.
• fixation elements can be provided which are configured to engage specific portions of the vertebra.
• one such fixation element is a spinal compression/distraction hook. This type of spinal hook is used to anchor the rod typically by engaging the laminae of the vertebra.
• Another fixation element is a spinal screw, which includes cancellous threads for engagement within the pedicle of a vertebra.
• TSRH® spinal fixation system sold by Danek Medical, Inc.
• a spinal hook such as the hook H shown in FIG. 1 for example, is engaged to an elongated fixation rod R by way of an eyebolt assembly E.
• a nut N is then threaded onto a threaded post of the eyebolt to clamp the hook yoke between the nut and the fixation rod R.
• the eyebolt E and the yokes of the hook H provide three degrees of fixation as represented by the arrows in FIG. 1.
• TSRH® spinal implant system are disclosed in the "TSRH® Surgical Technique Manual" provided by Danek Medical, Inc., published in 1990, which disclosure is incorporated herein by reference.
• a spinal hook 10 shown in FIGs. 3 and 4 includes a shoe 11 having a bone engaging surface 12.
• the bone engaging surface 12 can be formed in any known shape to engage a laminae of a vertebra, for ' instance.
• Integral with the shoe 11 is a top portion 13 that forms a pair of posts 14 disposed apart from each other in the form of a U-shaped yoke to define a slot 15 therebetween.
• the slot 15 is wide enough to receive an eyebolt assembly therein, such as eyebolt assembly E shown in FIGS. 1 and 2.
• a pair of coaxial grooves 16 are formed in each lateral surface 18 of the hook 10 to receive a portion of a spinal rod, such as rod R shown in FIGS. 1 and 2. These rod grooves 16 are present on each opposite lateral surface 18 of the posts 14 so that the hook 10 can be oriented on either side of a spinal rod. Slots 17 are provided on each end face 19 for engagement by a hook-holding insertion instrument .
• the upper portion 13 and posts 14 can be referred to as a "central post" configuration of fixation element 10.
• a similar central post configuration can be utilized with fixation elements other than hooks, such as bone bolts or screws. Leaving the details of the newly developed central post vertebral fixation elements to its pending application, it can be appreciated that the central post hook 10, of FIGS.
• Ratchet type wrench systems are typically not acceptable in procedures of this sort due to the risk of trauma to the surrounding tissue and the greater lateral clearance required to receive the ratchet mechanism at the surgical site.
• an eyebolt assembly comprising the eyebolt E and nut N, for engaging the fixation elements to the spinal rod.
• eyebolts are very convenient to the surgeon and are relatively easy and inexpensive to produce.
• One particular advantage of utilizing the eyebolt to engage the fixation element to the rod is the ability to provide a three-point clamp between the top portion 13 of the fixation element 10 and the rod R. This three-point clamp restricts relative movement between these two components in all six degrees of freedom so that a rigid construct can be formed. While there are advantages to retaining the eyebolt assembly approach to connecting the fixation element to the rod, the prevailing disadvantage of the side-tightening aspect of this approach frequently makes use of an eyebolt assembly cumbersome.
• One cog in this worthwhile goal for minimally invasive spinal surgical techniques is to provide an improved means for clamping the various vertebral fixation components to a spinal rod in a patient.
• Such a system should eliminate the side-tightening requirement of prior art systems to thereby minimize the intrusion into the patient.
• such a system should retain the versatility achieved by newly developed central post fixation elements. It is the goal of the present invention to address this and other concerns.
• an attachment plate for use with a spinal rod system to convert a normally side-tightening eyebolt to a top-tightenable arrangement for engaging spinal fixation elements to the spinal rod.
• the plate is configured for use with spinal fixation elements having a posteriorly projecting central post, one lateral surface of the post contacting the spinal rod when the rod extends through an aperture of the eyebolt.
• An eyebolt assembly is used to engage the fixation element to the spinal rod, which assembly includes an eyebolt body having an aperture for receiving the spinal rod and a threaded post projecting from the body to receive a nut threaded thereon.
• the attachment plate is generally L-shaped with a slot in an eyebolt engaging portion for receiving the threaded post of the eyebolt.
• the plate further includes an anteriorly projecting clamping portion configured for engaging the fixation element post.
• the clamping portion includes a flange portion having a surface configured to engage the lateral surface of the fixation element post opposite the spinal rod.
• the attachment plate includes a segment performing a camming function to provide a clamping force component directed toward the flange portion of the plate to thereby tightly clamp the spinal rod to the fixation element post when a nut is threaded onto the eyebolt threaded post.
• the plate includes a lower surface with a cam portion oriented to contact the spinal rod with the attachment plate disposed between the rod and the eyebolt assembly nut.
• the cam portion is configured to urge the spinal rod toward the flange portion of the attachment plate as the eyebolt nut is tightened down on the eyebolt post against the upper surface of the attachment plate. In this manner, the eyebolt nut is top-tightenable, that is, accessible posteriorly when the system is implanted adjacent a patient's spine.
• the eyebolt engaging portion is generally a flat plate that includes a sloped recess in its upper surface adjacent the eyebolt nut.
• the recess is sloped toward the flange portion of the attachment plate.
• the eyebolt nut includes a spherical surface which is received within the recess in the attachment plate.
• the spherical nut surface advances down the sloped recess to its final seating position. Movement of the nut down the sloped recess forces the eyebolt closer to the fixation element post so that the spinal rod is clamped between the aperture of the eyebolt and the surface of the fixation element post.
• the attachment plate provides means for converting an otherwise side-tightened eyebolt to a top-tightenable eyebolt, thereby greatly facilitating connection of spinal fixation elements to a spinal rod.
• the spinal fixation element such as a spinal hook
• the spinal rod is disposed within the patient adjacent the post of the fixation element.
• An eyebolt is threaded onto the rod and is arranged on the rod adjacent the fixation element post with the eyebolt threaded post also projecting posteriorly.
• the attachment plate is then installed with the flange portion being first placed in contact with the post of the fixation element.
• the attachment plate is then pivoted anteriorly until the eyebolt engaging portion of the plate is aligned laterally across the spinal rod and eyebolt body with the eyebolt threaded post extending through the slot in the attachment plate.
• the eyebolt nut is then threaded onto the eyebolt threaded post until it contacts the attachment plate eyebolt engaging portion.
• the camming segments of the attachment plate urge the spinal rod into firm contact with the fixation element post as the nut is tightened further down against the attachment plate.
• the attachment plate of the present invention provides a significant benefit in that it permits the use of eyebolts to engage fixation elements to a spinal rod, while providing means to allow top-tightening of the eyebolt nuts.
• Prior systems rely upon access to the nuts lateral to the components, or side-tightening.
• the present attachment plate allows the eyebolt to be rotated on the spinal rod so that the threaded eyebolt post is projecting posteriorly to a more readily accessible, position for the surgeon. Further, tightening the eyebolt nut against the attachment plate increases the clamping force of the rod to the fixation element to produce a rigid construct.
• a further object of the present invention is to provide a component that enhances the clamping force between the spinal rod and the fixation element to form a rigid construct.
• FIG. 1 shows a spinal hook of known design engaged to a fixation rod by way of an eyebolt assembly, as configured in accordance with one prior art system, the TSRH® spinal system.
• FIG. 2 is a side view showing the prior art system depicted in FIG. 1 in which a standard fixation hook is engaged about the laminae of a lumbar vertebra.
• FIG. 3 is a side elevational view of the spinal hook of recent design for which the top-tightening clamp assembly of the present invention is configured to engage.
• FIG. 4 is an end elevational view of the spinal hook shown in FIG. 3.
• FIG. 5 is a side elevational view of the attachment plate assembly in accordance with one embodiment of the present invention, shown clamping a spinal hook of the type shown in FIG. 4 to a spinal rod.
• FIG. 6 is a top elevational view of the attachment plate shown in FIG. 5.
• FIG. 7 is a side elevational view of an alternative embodiment of the attachment plate in accordance with the present invention.
• FIG. 8 is a top elevational view of the attachment plate shown in FIG. 7.
• FIG. 9 is an end cross-sectional view of the attachment plate shown in FIG. 8 taken along line 9-9 as viewed in the direction of the arrows.
• the present invention contemplates a system for engaging a vertebral fixation element to a spinal rod. More particularly, the fixation element is configured as shown in FIGs. 3 and 4 having a top portion 13 that forms a pair of posts 14 defining a slot 15 therebetween in a "central post" configuration. It is understood that although in the specific embodiments disclosed herein the fixation element is a spinal hook, the same "central post" approach can be applied to other types of vertebral fixation components, such as a bone screw. Whether the fixation element is a hook or a screw, it is engaged with the vertebra first and then clamped to the spinal rod using an eyebolt assembly.
• an attachment plate 25 which includes an eyebolt engaging portion 27 and a fixation element clamping portion 29.
• An eyebolt assembly 30 is provided which is modified somewhat from the eyebolt E shown in FIG. 1.
• the eyebolt assembly 30 includes an eyebolt body 31 having a central aperture 32 therethrough for receiving a spinal rod R therethrough.
• a threaded post 33 projects from a surface of the eyebolt body 31. The post 33 is adapted to engage a machine threaded nut 34 in a known manner.
• a central difference between this eyebolt assembly 30 and other more conventional eyebolts is that the threaded post 33 is longer so that it can receive the attachment plate 25 thereon.
• the attachment plate 25, and particularly the eyebolt engaging portion 27 is forked, as shown in FIG. 6.
• the eyebolt engaging portion includes a pair of arms 36 which define a slot 37 therebetween.
• the slot 37 is wide enough to receive at least the threaded post 33 of the eyebolt assembly 30 therethrough.
• the eyebolt engaging portion 27 also includes an upper surface 38 against which the eyebolt nut 34 is threaded.
• the width of slot 37 cannot exceed the flat width of the nut 34 and is preferably sufficiently narrower than the nut to provide solid purchase against the upper surface 38 when the nut is tightened thereon.
• the eyebolt engaging portion 27 further includes a lower rod engaging surface 40.
• This rod engaging surface is formed on each of the arms 36 and is preferably curved to accommodate the spinal rod R, and to operate as a cam surface as described herein.
• the lower rod engaging surface 40 spans about one-fifth of the circumference of the spinal rod.
• Most of the rod engaging surface 40 contact the spinal rod R at a posterior surface 41 (as viewed when engaged within the patient), and further includes a segment lateral to the spinal rod, which segment is designated 41 ⁇ l in FIG. 5.
• the rod engaging surface, and particularly the lateral segment 41 J ⁇ LI acts as a camming surface to provide a firm clamping force against the spinal rod R.
• the attachment plate 25 further includes a fixation element clamping portion 29 which is more particularly defined by an anterior projecting flange 43.
• the end of the flange 43 is formed into a projection 45 which is configured to engage the coaxial grooves 16 in one lateral surface 18 of the fixation element 10.
• this projection 45 has a curvature substantially identical to the curvature of the coaxial grooves 16 so that the projection will fit snuggly within the grooves when the assembly is completed.
• the attachment plate 25 includes insertion instrument slots 47 in the eyebolt engaging portion, and particularly in opposite faces of the arms 36. As with the fixation element, the instrument holding slots 47 provide a means for the plate to be held by an insertion instrument during the instrumentation procedure.
• attachment plate 25 and its relation to the fixation element and rod, the manner of use of the plate should be readily apparent. It is contemplated with use of the present invention that the surgeon would have already positioned various fixation elements, such as hook 10, at appropriate vertebral levels. A properly positioned fixation element will have its top portion 13, and particularly the central posts 14, projecting posteriorly. Several eyebolt bodies 31 can be pre-threaded onto the spinal rod prior to its location adjacent the spine.
• each eyebolt body 31 is positioned between the posts 14 of a corresponding fixation element 10 so that the rod R extending through the eyebolt aperture 32 contacts the coaxial grooves 16 on one side of the hook central posts 14. Further, the eyebolt body is situated so that its threaded post 33 also projects posteriorly for easy access by the surgeon.
• the attachment plate 25 is top-loaded over the eyebolt assembly 30 and in contact with the fixation element 10. More particularly, the attachment plate 25 is loaded so that the projection 45 first engages the coaxial groove 16 on the side of the central posts 14 opposite the rod R engagement. The attachment plate is then pivoted anteriorly so that the lower rod engaging surface 40 contacts the spinal rod R as it is situated directly adjacent the fixation element 10. Some manipulation may be required to bring the rod R into contact with the fixation element 10, while simultaneously contacting the lower rod engaging surface 40 of the attachment plate 25.
• the slot 37 defined between the arms 36 is open at its end (as depicted in FIG. 6) to readily receive the eyebolt threaded post therein as the plate is pivoted anteriorly. Alternatively, the slot 37 can be closed at both ends. A closed slot 37 increases the complexity of the installation of the plate by requiring that the eyebolt assembly 30 be rotated about the rod R somewhat so the post
• the post 33 is oriented at an angle. With the post 33 so oriented, the slot 37 will slide over the post 33 when the plate is rotated. As the plate 25 is rotated closer to the rod, the post 33 will also naturally rotate to its normal installed posterior facing position.
• the attachment plate 25 provides a ready means for converting an otherwise side loading eyebolt assembly into a top-loading eyebolt assembly for engaging a fixation element.
• the slot 37 in the attachment plate 25 allows for easy manipulation of the eyebolt and spinal rod relative to the fixation element until final clamping is desired.
• the lateral segment 41 ⁇ acts as a camming surface to gradually urge the spinal rod R into a firmer engagement with the coaxial groove 16 on one lateral surface 18 of the fixation element 10.
• the lateral segment 41 ⁇ provides a clamping force component directed toward the clamping portion flange 43 and particularly toward the projection 45. Simultaneously, the clamp engagement between the projection 45 and coaxial groove 16 on the other side of the fixation element is also increased.
• the rod engaging surface 40 including the lateral segment 41 , is curved, preferably at approximately the same radius as the spinal rod.
• the lateral segment 41 r can assume other configurations, provided that a lateral clamping force component is exerted by the rod engaging surface 40 against the spinal rod R.
• a lateral segment 41 that is oriented at an angle relative to both the posterior and lateral directions will provide such a clamping force component as the rod R slides against the angled segmen .
• FIGS. 7 through 9 An alternative embodiment of the present invention is shown in FIGS. 7 through 9. Specifically, an attachment plate 50 is shown which does not include the same lower rod engaging surface 40 as the attachment plate 25 of FIG. 5.
• the attachment plate 50 does include an eyebolt engaging portion 52 and a fixation element clamping portion 53.
• the fixation element clamping portion 53 also includes an anterior projecting flange 55 terminating in a projection 56 which is configured to engage the coaxial groove 16 in one lateral surface 18 of the fixation element 10.
• the plate 50 includes a pair of arms 59 which define a slot 60 therebetween configured to receive the threaded post 33 of the eyebolt assembly 30 therethrough.
• the slot 60 is narrower than the eyebolt body 31 so the lower surface 61 of the plate 50 can contact the upper surface 35 of the eyebolt body.
• the attachment plate 50 instead of the camming action provided by the lower rod engaging surface 40 of the plate 25, the attachment plate 50 includes a sloped recess 62 defined in the upper surface 63 of the eyebolt engaging portion 52. This sloped recess 62, or camming surface, is configured to -engage a lower spherical surface 65 of a specifically configured nut , 66.
• the recess 62 slopes from end 62a at the open end of the arms 59 toward the portion 62b adjacent the inner end of the slot 60.
• the recess 62 slopes toward the anteriorly projecting flange 55 so that the eyebolt nut 66 is drawn in that direction as it is tightened onto the threaded post.
• This sloped recess 62 serves the same camming function as the lower rod engaging surface 40 of the previous embodiment. More particularly, as the nut 66 is threaded onto the post 33, the lower spherical surface 65 contacts the sloped recess 62.
• the spherical surface 65 gradually slides down the sloped recess 62 until it seats at the end portion 64 of recess 62 the attachment plate 50.
• the interaction between the lower spherical surface 65 of the nut 66 and the sloped recess 62 of the attachment plate 50 draws the threaded post 33 closer to the fixation element 10.
• the eyebolt body 31 naturally follows with the threaded post 33 so that the body too is forced closer to the fixation element central post 15. In this manner the spinal rod R is forced to contact the walls of the aperture 32 of the eyebolt body 31 generally lateral to the fixation element 10 at the same time that the rod R contacts the groove 16 in the one surface of the fixation element post 15.
• the rod R is then clamped between the eyebolt and the fixation element 10, while the fixation element 10, and more particularly the central post 14, is clamped between the projection 56 of the attachment plate and the spinal rod R.
• the plate itself is clamped between the upper surface 35 of the eyebolt body and the nut 66.
• the attachment plate 50 is loaded and engaged to the fixation components in a manner similar to that described in connection with attachment plate 25 of the previous embodiment .
• the attachment plates 25 and 50 are preferably formed of 316L stainless steel having a tensile strength of about 125 ksi. However, other biocompatible materials may be suitable for forming the attachment plate.
• the plates 25 and 50 facilitate installation of the plates, this same shape can lead to stress concentrations at the intersection between the eyebolt engaging portion and the anterior projecting flange.
• the plates must be strong enough to withstand bending, particularly at the joint between the flange 43 and the eyebolt engaging portion, such as portion 27 of the plate 25.
• the internal and external corners at this joint between the two portions are preferably rounded, as shown in FIGS. 5 and 7, to reduce the likelihood of stress concentrations forming at that intersection. It is understood that this portion of the attachment plate 25 will endure a significant amount of load as the entire assembly is tightened to rigidly clamp the fixation element 10 to the spinal rod R.

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• Health & Medical Sciences (AREA)
• Orthopedic Medicine & Surgery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Neurology (AREA)
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• Heart & Thoracic Surgery (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Medical Informatics (AREA)
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• 1993
  • 1993-08-19 US US08/109,088 patent/US5437670A/en not_active Expired - Lifetime
• 1994
  • 1994-08-12 TW TW084107381A patent/TW274047B/zh active
  • 1994-08-16 AU AU75667/94A patent/AU7566794A/en not_active Abandoned
  • 1994-08-16 WO PCT/US1994/009244 patent/WO1995005126A1/en active Application Filing
  • 1994-08-19 ZA ZA946319A patent/ZA946319B/xx unknown
• 1995
  • 1995-04-10 US US08/423,019 patent/US5624441A/en not_active Expired - Lifetime

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