US20050113924A1 - Apparatus and method for performing spinal surgery - Google Patents

Abstract

An embodiment of an intervertebral prosthetic device for implantation in a spine includes a rigid fixation member and a compressible member. The fixation member is configured to be placed in a cavity of a first vertebral body and against bone of the first vertebral body. The compressible member is configured to be placed in a cavity in an intervertebral disc and to be secured to the first fixation member. Another embodiment includes two compressible members and one fixation member. In this embodiment, the first and second compressible members are sized to substantially replace the nucleus pulposus of first and a second intervertebral discs, respectively, on either side of a vertebral body. The fixation member is sized to fit within a cavity in the vertebral body between the first and second compressible members.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This invention claims priority to co-pending U.S. Provisional Patent Application Nos. 60/492,966 (filed Aug. 7, 2003) and 60/512,186 (filed Oct. 20, 2003).
BACKGROUND
• This invention relates to the field of spinal surgery. More specifically, this invention relates to a novel implantable apparatus for replacing the functionality of one or more failing intervertebral discs, without fusing the vertebral bodies above and below the disc(s). This invention also relates to devices for implanting and securing the intervertebral prosthetic device in cavities in a vertebral body and in one or more adjacent intervertebral discs. The invention further relates to methods for performing spinal surgery.
• The human spine is a flexible structure comprised of twenty-three mobile vertebrae. Intervertebral discs separate and cushion adjacent vertebrae. The top and bottom surfaces of intervertebral discs abut vertebral body endplates. The intervertebral discs act as shock absorbers and allow bending between the vertebrae.
• An intervertebral disc comprises two major components: the nucleus pulposus and the annulus fibrosis. The nucleus pulposus is centrally located in the disc and occupies 25-40% of the disc's total cross-sectional area. The nucleus pulposus usually contains 70-90% water by weight and mechanically functions like an incompressible hydrostatic material. The annulus fibrosis surrounds the nucleus pulposus and resists torsional and bending forces applied to the disc. Thus, the annulus fibrosis serves as the disc's main stabilizing structure. A healthy disc relies on the unique relationship of the nucleus and annulus to one another.
• Individuals with damaged or degenerated discs often experience significant pain. The pain results, in part, from instability in the intervertebral joint due to a loss of hydrostatic pressure in the nucleus pulposus, which leads to a loss of disc height and altered loading of the annulus fibrosis.
• A conventional treatment for degenerative disc disease is spinal fusion. In one such surgical procedure, a surgeon removes the damaged natural disc and then fuses the two adjacent vertebral bodies into one piece. The surgeon fuses the vertebral bodies by grafting bone between the adjacent vertebrae and sometimes using metal rods, cages, or screws to hold the graft in place until the graft heals.
• Although spinal fusion may alleviate pain associated with degenerative disc disease, it also results in loss of motion at the fused vertebral joint. Lack of motion at the fused site puts additional stress on the discs above and below the fusion. The additional stress may cause the adjacent discs to degenerate and produce pain, thereby recreating the original problem.
• To remedy the problems associated with spinal fusion, various prosthetic devices have been developed either to replace the entire disc (i.e., the nucleus pulposus and the annulus fibrosis) with a prosthetic joint or to replace the nucleus pulposus of the damaged disc with a suitable biomechanical equivalent. Unfortunately, the previous approaches have certain limitations because conventional total disc replacement devices and nucleus replacement devices disrupt tissues that will not heal.
• In the case of total disc replacement surgery, existing prosthetic devices have met with limited success in reproducing the biomechanics of a natural disc. Moreover, the anterior longitudinal ligament must be severed as part of the anterior approach by which the device is implanted. Worse, the severing may span two vertebral bodies for a two level reconstruction, which can lead to lessened spinal function and stability. Further, total disc replacement devices require removal of a substantial portion the disc and attachment to the adjacent vertebral bodies. The endplates of the vertebral bodies are nonuniform and typically sclerotic, which prevents the close physical joining of endplate and device surfaces required for bone ingrowth to provide adhesion and can lead to subsidence of the disc replacement device into the bone of the vertebral bodies if the endplates are shaved for contour matching. Moreover, the devices display limited motion. Specifically, as a result of the oversized implant relative to the narrow disc space, total disc replacement often results in a range of motion of only about 3.8° to 4.6°. Such a limited range of motion is the equivalent of a spinal fusion, which is defined to be motion of less than about 5°.
• For example, U.S. Pat. No. 4,759,769 to Hedman et al. discloses a synthetic disc having upper and lower plates hinged together. Although the hinged disc allows forward bending between adjacent vertebrae, the hinged disc does not allow axial compression or lateral flexion. Nor does it allow axial rotation of the vertebral column at the site of the implant. Therefore, the Hedman et al. device lacks the biomechanics of a natural disc.
• Likewise, the prosthetic disc device disclosed in U.S. Pat. No. 4,309,777 to Patil does not replicate natural motion between adjacent discs. The Patil device includes two cups, one of which overlaps the other and is spaced from the other by springs. The cups move only in a single axial dimension. Thus, the Patil device does not enable natural flexion of the spine in any direction. In addition, the highly constrained motion of the Patil device can lead to high device/tissue interface stresses and implant loosening.
• In the case of nucleus replacement devices, historically these devices required perforation or partial excision of the annulus to insert the device. Breaking the continuity of the annular ring precludes normal stress loading of the annulus, which may be necessary for later healing. Further, degeneration of the annulus, exacerbated by damage done during implantation, may also result in increased loads placed upon the implant. Increased loads of this nature may lead to subsidence of the device into the vertebral body, device extrusion through the annular defect, or expulsion from the nuclear space. Moreover, these problems are exacerbated in the situation in which more than one disc is to be replaced because any or all of the devices may develop these problems. These problems are particularly challenging in the lumbar spine, where the discs are most highly stressed due to high bearing requirements.
• A remarkable intervertebral synthetic prosthetic device that greatly reduces the problems associated with total disc replacement and conventional nucleus replacement devices is disclosed in U.S. Pat. No. 5,827,328 (“the '328 patent”) to Buttermann. The Buttermann devices excise the nucleus pulposus while maintaining the biomechanical functionality of the intact annulus fibrosis. Moreover, the intervertebral prosthetic device permits at least four degrees of relative motion between two vertebral bodies on either side of targeted intervertebral disc. These degrees of relative motion include sagittal bending, coronal bending, axial rotation, and axial compression. Moreover, the compressible member permits small increments of translational movement between the vertebral bodies (i.e., fifth and sixth degrees of relative motion, namely anterior-posterior translation and side-to-side, or lateral, translation).
• FIG. 1 shows an embodiment of an intervertebralprosthetic device10 according to one embodiment of the '328 patent that is designed to replace a damaged natural disc. Thisdevice10 is implanted by making holes in two adjacent vertebral bodies and boring through the nucleus pulposus of the intervertebral disc between the vertebral bodies. Theintervertebral prosthetic device10 has afirst fixation member14, asecond fixation member16, and acompressible member18 that is positioned between thefirst fixation member14 and thesecond fixation member16. In addition to restoring the disc height, thecompressible member18 acts as a shock absorber to minimize impact loading and, thus, minimize device failure or vertebral fracture.
• Thefirst fixation member14 is positioned in a firstvertebral body20. Thesecond fixation member16 is positioned within a secondvertebral body22 adjacent the firstvertebral body20. Eachfixation member14,16 has anadjustable member28,30, respectively, and asupport member32,34, respectively. Controlling the height of theadjustable members28 and30, along with selecting an appropriately sized support member, controls the “disc” height. The disc height is defined as the axial distance between the vertebrae above and below the operative disc.
• Theadjustable member28 of thefirst fixation member14 has an imaginary first longitudinal axis (shown by double-arrowed line A-A inFIG. 1) andadjustment elements24 that allow adjustment of the height of theadjustable member28 substantially along its longitudinal axis. In the embodiment shown inFIG. 1, thesecond fixation member16 is structurally similar to thefirst fixation member14, but inverted. Theadjustable member30 of thesecond fixation member16 has a second longitudinal axis (shown by double-arrowed line B-B) andadjustment elements26 that allow adjustment of the height of theadjustable member30 substantially along its longitudinal axis.
• FIG. 4 shows one embodiment of thefirst fixation member14. In the embodiment shown inFIG. 1, thesecond fixation member16 is structurally similar to thefirst fixation member14, but inverted. Thus, the following discussion also applies to thesecond fixation member16.
• Theadjustable member28 of thefirst fixation member14 is adjustable in an axial direction byadjustment elements24. Theadjustment elements24 comprise telescopic struts extending between a first,outer plate31 and a second,inner plate33. Theouter plate31 is farther from the operative intervertebral disc and hence farther from thecompressible member18. In contrast, theinner plate33 is closer to the operative intervertebral disc area and hence closer to thecompressible member18. In the embodiment illustrated inFIG. 1, theouter plate31 has a bone-contactingsurface27, and theinner plate33 has asurface35 for positioning against thesupport member32.
• Theadjustment elements24 adjust the distance between the first bone-contactingplate31 and thesecond plate33, thus adjusting the height of theadjustable member28. A surgeon may adjust the telescopic struts to increase the height of the adjustable member and thus mechanically pre-load thecompressible member18 to reproduce the axial compression absorbed by a nucleus pulposus of a natural disc. Pre-loading the compressible member restores the intervertebral height at the operative joint, restores the function of the annulus fibrosis. Pre-loading also assures close apposition of aningrowth surface27,29 of the device tobone36,38.
• Each telescopic strut is provided with alock screw63 to adjust the length of thestrut24 and hence control the height of the adjustable member. Thelock screw63 may comprise, for example, a pin (not shown) that extends through both thetelescoping portion65 and thehousing portion67 of thestrut24. Eachstrut24 is independently adjustable.FIG. 5 shows a top view of thesecond plate33 of theadjustable member28. Theadjustment elements24 preferably are spaced equidistant from each other to enable specific height adjustment of various regions of the adjustable member.
• The first andsecond fixation members14 and16 have porous portions, such as the bone-contactingsurface27, to permit bone ingrowth. InFIG. 1, the bone-contactingsurface27 of theadjustable member28 is positioned against the subchondral bone of anendplate36 of the superiorvertebral body20, and the bone-contactingsurface29 of theadjustable member30 is positioned against the subchondral bone of anendplate38 of the inferiorvertebral body22. Alternatively, a biocompatible fabric or suitable material may be wrapped around the fixation members to enable bone ingrowth. As another alternative, a biocompatible coating may be applied to the fixation members to facilitate bone ingrowth. The prosthetic device ofFIG. 1 does not require conventional mechanical attachments, such as pegs or screws, to hold the prosthesis permanently in place. The intravertebral (i.e., within a vertebral body) positioning of thefixation members14,16 maintains theprosthetic device10 in stable relationship at the operative intervertebral joint. The prosthetic device, however, may include mechanical or other attachments to supplement the porous portions of the fixation members and to temporarily fix the prosthetic device in place until bone ingrowth has occurred.
• To further promote bone ingrowth, theadjustment elements24 may includefins66 extending outward from an exterior surface of theelement24, as shown inFIG. 4. Thefins66 increase the surface area of thefixation member14 to which bone may attach. Preferably, thesefins66 are located on the adjustment elements that are positioned on the anterior side of theadjustable member28. The prosthetic device also may include protuberances (not shown) on the bone-contacting surface of the adjustable members to increase the surface area of the porous portion of the fixation members and, thus, encourage bone ingrowth.
• FIG. 6 shows a cross-section ofsupport member32. Thesupport member32 has afirst surface72 that operably faces away from thecompressible member18 and asecond surface74 that operably faces towards thecompressible member18. The first andsecond surfaces72 and74 are oblique so that acircumferential surface77 around thesupport member32 varies in width, as shown inFIG. 4. Thus, thesupport member32 is wedge-shaped. In other words, thesupport member32 preferably tapers from a maximum thickness at oneside73 to a minimum thickness at anopposite side75. Generally, thesupport member32 is thicker on the side of thefixation member14 placed anteriorly in a patient's spine to account for the spine's natural curvature.
• The support members are constructed with various thicknesses and with various angled surfaces, depending upon the vertebral level of the operative intervertebral joint. An angle θ shown inFIG. 6 ranges between 3°-10°. The support members are shaped to maintain sagittal alignment. Maintaining sagittal alignment avoids nonuniform loading of the compressible member and avoids early fatigue failure of that member.
• Thecompressible member18, which is shown inFIG. 2, can comprise at least one spring and, in the illustrated embodiment, comprises a plurality ofsprings40. Thecompressible member18, which is implanted in the region of an excavated nucleus pulposus of the operative intervertebral disc, is dimensioned so that the annulus fibrosis of the natural disc is at least substantially (if not completely) maintained. As a result, the intervertebral prosthetic device restores the mechanical properties of the disc without disrupting the annulus fibrosis. Retention of the annulus fibrosis maintains stability of the intervertebral joint at the implant site. In addition, the annulus fibrosis serves as a boundary for the compressible member and, therefore, minimizes the potential for accidental dislodgment of the prosthetic device.
• Thecompressible member18 has atop plate42, abottom plate44, and a plurality ofcoil springs40 extending between thetop plate42 and thebottom plate44. Thetop plate42 has a first surface46, which is connectable to thefirst fixation member14, and asecond surface48. Thebottom plate44 also has afirst surface50, which is connectable to thesecond fixation member16, and asecond surface52. Thesprings40 extend between thesecond surfaces48 and52 of thetop plate42 andbottom plate44, respectively.
• When pre-loaded, thecompressible member18 can have an axial height of approximately 1.5 cm, greatest at the L45 vertebral level and slightly less at the upper lumbar vertebrae. The coil springs40 can have non-linear stiffness so that they become stiffer at higher applied loads; the nonlinear stiffness simulates physiological intervertebral stiffness. Moreover, any spring arrangement may be used that achieves sufficient axial compressive stiffness to replicate the biomechanics of the natural disc.
• The compressible member includes an imaginary longitudinal axis (shown by the dashed line C-C) and an outer periphery in a plane transverse to its longitudinal axis. A largest dimension of the compressible member's outer periphery is less than or substantially equal to the diameter of a nucleus pulposus of the natural intervertebral disc. Put another way, the annulus fibrosis of the natural disc, which is substantially (if not completely) preserved during the implantation procedure, circumscribes thecompressible member18. For example, where the compressible member comprises a plurality of springs, the outer periphery of the compressible member circumscribes the springs, and the largest dimension of that outer periphery may extend to, but does not extend beyond, the nucleus pulposus. In other embodiments, where the compressible member includes a top plate and a bottom plate, and where those plates fit within the annulus fibrosis and extend beyond the outermost portions of the springs, the outer periphery of the compressible member equals the larger of the two plate peripheries. In quantitative terms, the outer periphery of the compressible member preferably ranges between 2.0 cm to 3.0 cm, which approximates the diameter of the nucleus pulposus of a natural intervertebral disc.
• FIGS. 3A-3C show three embodiments of a coil spring designed to possess non-linear stiffness. In the embodiment ofFIG. 3A, thecoil spring54 has a variable, or non-uniform,cross-sectional diameter56.FIG. 3B shows another embodiment in which acoil spring58 has avariable pitch60, where the pitch is defined as the distance between successive coils of thespring58.FIG. 3C shows a third embodiment of acoil spring62 in which at least two of the spring coils havedifferent radii64 measured from an imaginary axis D-D extending along the central axis of thespring62.
• A method of intervertebral disc replacement now will be described in connection withFIGS. 8-14.FIG. 8 shows a pathologicalintervertebral disc90 located between a superiorvertebral body92 and an inferiorvertebral body94. Prior to implantation, a surgeon performs a partial vertebrectomy to excise bone matter from the superiorvertebral body92 for receipt of a fixation member. This procedure can be performed using a cutting guide and reamer. Bone harvested from thevertebral body92 by the reamer can be used after implantation of the prosthetic device to promote bone ingrowth into the prosthetic device, as later described. The partial vertebrectomy creates a cavity bounded by subchondral bone of adistant endplate96 and subchondral bone of anear endplate98 of the superiorvertebral body92.FIG. 9 shows a cross-sectional view of the superiorvertebral body92 after the partial vertebrectomy, as taken along line9-9 inFIG. 8.
• The surgeon next excises the nucleus pulposus of the damaged disc to create acavity100, as shown inFIG. 10, for receipt of the compressible member. Theannulus fibrosis102, seen inFIG. 11, is maintained.
• Upon completion of the partial vertebrectomies, the surgeon implants afixation member104 into the inferiorvertebral body94, as shown inFIG. 11. The surgeon can select a support member with an appropriate thickness to accommodate the angulation at the operative intervertebral levels. The surgeon then inserts a compressible member106 (via the cavity formed in the superior vertebral body92) into the cavity formerly containing the nucleus pulposus of the damaged disc and connects it to theinferior fixation member104, as shown inFIG. 12. Thecompressible member106 and thefixation member104 may be connected by conventional attachment members, such as screws, or by biocompatible cement or a suitable adhesive composition. Finally, the surgeon implants another fixation member, similar to the one implanted in the inferiorvertebral body94, yet inverted, in the superiorvertebral body92. Connection of that fixation member to thecompressible member106 forms an intervertebral prosthetic device like the one shown inFIG. 1.
• Once the fixation members are in place, the surgeon expands each adjustable member. The surgeon applies distraction until the adjustable member is seated against the subchondral bone anddistant endplate96 of the vertebral body and until the desired compression has been applied to the compressible member. The adjustment elements of the adjustable member are then secured, e.g.,FIG. 13 shows rotation of the lock screws112 of individualtelescopic struts108 to secure the struts at an appropriate height.
• The surgeon next packscancellous bone grafts118, typically obtained during creation of the cavity in the vertebral body, around the struts of each adjustable member, as shown inFIG. 14. The growth of bone around the fixation member and into its porous surfaces secures the intervertebral prosthetic device in place, absent mechanical attachments typically used in conventional disc prostheses. The surgeon then replaces the cortical bone from the partial vertebrectomy procedure and, if needed, secures it with a bone screw, suture or bone cement. In certain clinical situations, as when there is poor bone healing or insufficient bone, the surgeon may elect to use bone cement to attach the fixation members to the vertebrae.
• Although the embodiment shown inFIGS. 1-6 is effective, in some instances it may be unnecessarily invasive as a result of its implantation via two vertebral body holes.FIG. 7 shows a second, less invasive embodiment described in the '328 patent, in which a prosthetic device is implanted via one vertebral body hole.
• FIG. 7 shows an intervertebralprosthetic device76 according to this second embodiment that comprises afirst fixation member78, asecond fixation member80, and acompressible member82. Thecompressible member82 is positioned between the first andsecond fixation members78,80. Thesecond fixation member80 comprises a wedge-shaped support member with anupper surface84 that attaches to thecompressible member82 and alower surface86 that rests upon subchondral bone of anear endplate88 of an inferior vertebral body. In this embodiment, adjustment of thefirst fixation member78 pre-loads thecompressible member82 to an appropriate extent. Also, in this embodiment, alower surface86 of thesupport member80 may be composed of a porous material and may have a slightly convex shape to match the natural contour of the near endplate of the inferior vertebral body.
• The implantation of theFIG. 7 embodiment is similar to the implantation of theFIG. 1 embodiment. Specifically, similar to the embodiment shown inFIG. 10, a cavity may be formed in the superiorvertebral body92 and then extended through the nucleus pulposus of the intervertebral disc therebelow. At this time, the compressible member with thelower fixation member80 affixed thereto may be inserted through the cavity in the vertebral body and then pushed downward into thecavity100 in the intervertebral disc. Subsequently, theupper fixation member78 is: (a) positioned in the cavity formed in the superiorvertebral body92; (b) connected to the compressible member; and (c) adjusted in the manner previous discussed with respect to theFIG. 1 embodiment. Of course, the cavity in the superiorvertebral body92 is then closed also in the manner previously described.
• As evident from the embodiments ofFIGS. 1 and 7, the intervertebral prosthetic device embodiments have a modular design so that the prosthesis may be sized to the patient's anatomy and designed for the patient's condition. The modular design also enables replacement of individual components of the prosthesis (i.e., a fixation member or a compressible member), rather than replacement of the entire prosthesis should one component fail. As a result, the compressible member can be attached to the fixation members by mechanical attachments, such as screws, rather than bone cement so that a surgeon may easily replace damaged or worn components.
• Unfortunately, the embodiment shown inFIG. 1 precludes use when reconstructing multiple adjacent discs. Additionally, although the less invasive embodiment shown inFIG. 7 may be implanted via only one vertebral body hole, it may be less effective than the embodiment shown inFIG. 1 when used in patients with low bone density. Specifically, theFIG. 7 may be less effective as a result of inability to adequately fix thelower fixation member80 to the vertebral body below the compressible member. Further, this inability to adequate fix thelower fixation member80 may, in turn, lead to subsidence of the device into the vertebral body adjacent thelower fixation member80.
SUMMARY
• An embodiment of the invention addresses a prosthetic device that includes: a first compressible member sized to substantially replace the nucleus pulposus of a first intervertebral disc; a second compressible member sized to substantially replace the nucleus pulposus of a second intervertebral disc that is separated from the first intervertebral disc by a vertebral body; and a fixation member sized to fit within a cavity in the vertebral body between the first and second compressible members.
• Another embodiment of the invention addresses a prosthetic device that includes: a fixation member sized to fit within a cavity in a first vertebral body; and a compressible member sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body. A first side of the compressible member is configured to engage the fixation member and a second side of the compressible member is configured to engage a second vertebral body. The second side of the compressible member is configured to fit within a seat formed in the cortical bone of the endplate of the second vertebral body.
• Another embodiment of the invention addresses an intervertebral prosthetic device for implantation in a spine that includes: (a) a rigid fixation member having a fixed length, the rigid fixation member being configured to be placed in a cavity of a vertebral body and against bone of the vertebral body; and (b) a first compressible member configured to be placed in a cavity in a first intervertebral disc adjacent the vertebral body and to be secured to the rigid fixation member. The compressible member is constructed to remain compressible after implantation and has at least one compressible element that remains compressible after implantation. The rigid fixation member is sized to compress the compressible member a predetermined amount when the rigid fixation member and the first compressible member are placed in the cavity in the first vertebral body and in the cavity in the first intervertebral disc, respectively.
• Another embodiment of the invention addresses an intervertebral prosthetic device for implantation in a spine. This device includes: (a) a fixation member configured to be placed in a cavity of a vertebral body, the fixation member including: (i) an outer member configured to be placed against bone of the vertebral body; (ii) an inner member opposite the outer member; and (iii) at least one adjustment element that extends between the outer and inner members and that is configured to adjust a length dimension of the fixation member along its longitudinal axis; (b) a compressible member configured to be placed in a cavity in an intervertebral disc adjacent the vertebral body and configured to be secured to the inner member of the fixation member; and (c) a spacer sized to fit between the outer and inner members of the fixation member to maintain the fixation member at a desired length dimension.
• Another embodiment of the invention addresses an intervertebral prosthetic device for implantation in a spine. This device includes: (a) a fixation member configured to be placed in a cavity of a vertebral body, the fixation member including: (i) an outer member configured to be placed against bone of the vertebral body; (ii) an inner member opposite the outer member; and (iii) a longitudinal axis extending between the outer and inner members; and (b) a compressible member configured to be placed in a cavity in an intervertebral disc and to be secured to the inner member of the fixation member. The compressible member is constructed to remain compressible after implantation. The outer member includes a tab extending outward along an axis different from the longitudinal axis.
• Another embodiment of the invention addresses an intervertebral prosthetic device for implantation in a spine. This device includes: (a) a fixation member configured to be placed in a cavity of a vertebral body, the fixation member including: (i) an outer member configured to be placed against bone of the vertebral body; (ii) an inner member opposite the outer member; and (iii) a longitudinal axis extending between the outer and inner members; (b) a compressible member configured to be placed in a cavity in an intervertebral disc adjacent the vertebral body and to configured be secured to the fixation member; and (c) at least one anchor element configured to immobilize and/or stabilize the compressible member and/or the fixation member.
• Another embodiment of the invention addresses a prosthetic device that includes: (a) a fixation member sized to fit within a cavity in a first vertebral body; and (b) a compressible member that includes: (i) a cup-shaped base member; (ii) an upper member; and (iii) one or more compressible elements provided between the base member and the upper member. The compressible member is sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body.
• Another embodiment of the invention addresses a prosthetic device that includes: (a) a fixation member sized to fit within a cavity in a first vertebral body; and (b) a compressible member that includes: (i) a base member; (ii) an upper member that includes a spike; and (iii) one or more compressible elements provided between the base member and the upper member. The one or more compressible elements are sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body.
• Another embodiment of the invention addresses a prosthetic device that includes: (a) a fixation member sized to fit within a cavity in a first vertebral body; and (b) a compressible member that includes: (i) a base member; (ii) an upper member comprising a ball-and-socket joint; and (iii) one or more compressible elements provided between the base member and the upper member. The compressible member is sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body.
• Another embodiment of the invention addresses a prosthetic device that includes: (a) a fixation member sized to fit within a cavity in a first vertebral body; and (b) a compressible member that includes: (i) a base member; (ii) an upper member; and (iii) one or more compressible elements provided between the base member and the upper member. The compressible member is sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body. The base member is adjustable in a radial direction.
• Another embodiment of the invention addresses a method of spinal prosthetic implantation. This method includes: (a) creating a cavity in a first vertebral body; (b) cutting a first hole through either a lower or an upper endplate of the vertebral body and through the nucleus pulposus of a first intervertebral disc adjacent thereto, thereby creating a first opening in the first intervertebral disc; (c) cutting a second hole through the other of the lower and upper endplate of the vertebral body and through the nucleus pulposus of a second intervertebral disc adjacent thereto, thereby creating a second opening in the second intervertebral disc; (d) implanting a first compressible member into one of the first and second openings; (e) implanting a second compressible member into the other of the first or second openings; and (f) implanting a fixation member into the cavity in the first vertebral body.
• Another embodiment of the invention addresses a method of spinal prosthetic implantation. This method includes: (a) creating a cavity in a first vertebral body; (b) cutting through an endplate of the vertebral body and through the nucleus pulposus of an adjacent intervertebral disc, thereby creating an opening in the intervertebral disc; (c) cutting into the cortical bone of a second vertebral body on the other side of the intervertebral disc to create a seat; (d) implanting a compressible member into the opening in the intervertebral disc such that a distal end of the compressible member sits within the seat in the second vertebral body; and (e) implanting a fixation member in the cavity in the first vertebral body.
• Another embodiment of the invention addresses a method of spinal prosthetic implantation. This method includes: (a) creating a cavity in a vertebral body; (b) cutting a hole through either a lower or an upper endplate of the vertebral body and through the nucleus pulposus of an intervertebral disc adjacent thereto, thereby creating an opening in the intervertebral disc; (c) implanting a compressible member into the opening in the intervertebral disc; and (d) implanting a fixation member into the cavity in the first vertebral body. The compressible member comprises a base member that is wider than the hole cut in the vertebral body through which the first compressible member is implanted. The step of implanting the compressible member into the opening includes: (i) maneuvering the base member of the compressible member so that it passes through the hole and into the opening; and (ii) rotating the base member so that it substantially covers the hole.
• Another embodiment of the invention addresses a method of spinal prosthetic implantation. This method includes: (a) creating a cavity in a vertebral body; (b) cutting a hole through either a lower or an upper endplate of the vertebral body and through the nucleus pulposus of an intervertebral disc adjacent thereto, thereby creating an opening in the intervertebral disc; (c) implanting a compressible member into the opening in the intervertebral disc; and (d) implanting a fixation member into the cavity in the first vertebral body. The compressible member comprises a base member that is radially adjustable to be wider than the hole cut in the vertebral body through which the compressible member is implanted. The step of implanting the compressible member into the opening includes: (i) maneuvering the base member of the compressible member so that it passes through the hole and into the opening; and (ii) radially adjusting the base member so that it substantially covers the hole.
• Another embodiment of the invention addresses a drill guide for use in spinal surgery. The drill guide includes a body having a first leg and a second leg. The first leg is dimensioned to be fixed relative to an intervertebral prosthetic member mounted in a cavity of a first vertebral body. The second leg is dimensioned to extend from the first leg, adjacent the first vertebral body, to a free end, adjacent at least one of an intervertebral disc and a second vertebral body. The second leg includes at least one drilling channel extending through the second leg and the free end of the second leg comprises a drill positioning block through which the at least one drilling channel extends.
• It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a presently preferred embodiment of the invention, and, together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention.
• FIG. 1 is a schematic, cut-away side view of a prior art intervertebral prosthetic device implanted in a spine.
• FIG. 2 is a top perspective view of a compressible member of the intervertebral prosthetic device ofFIG. 1.
• FIGS. 3A-3C are top perspective views of different embodiments of a spring of the compressible member shown inFIG. 1.
• FIG. 4 is a top perspective, partially exploded view of a fixation member of the intervertebral prosthetic device ofFIG. 1 and shows an adjustable member and a support member.
• FIG. 5 is a top view of a plate of the adjustable member shown inFIG. 1.
• FIG. 6 is a side view, in cross-section, of the support member shown inFIG. 1.
• FIG. 7 is a schematic, cut-away side view of another prior art intervertebral prosthetic device implanted in a spine.
• FIG. 8 is a schematic, cut-away side view showing subchondral bones of a superior vertebral body after a partial vertebrectomy.
• FIG. 9 is a sectional view of a vertebra after creating a cavity within the vertebral body, as taken along line9-9 ofFIG. 8.
• FIG. 10 is a schematic, cut-away side view of a vertebral joint area after creating a cavity within the vertebral body and excision of a nucleus pulposus of a natural disc.
• FIG. 11 is a schematic, cut-away side view of a vertebral joint and shows a fixation member, including an adjustable member and a support member, implanted in an inferior vertebral body.
• FIG. 12 is a schematic, cut-away side view of a vertebral joint and shows a compressible member implanted in an intervertebral joint.
• FIG. 13 is a schematic, cut-away side view of a vertebral joint and shows a technique for adjusting the height of an adjustable member implanted in a superior vertebral body.
• FIG. 14 is a schematic, cut-away side view of a vertebral joint and shows a technique for bone grafting an adjustable member in a superior vertebral body.
• FIG. 15A is a top perspective view of an intervertebral prosthetic device and a drill guide used to drill holes in the intervertebral bone in accordance with the invention;FIGS. 15B-15D are a first side elevation view, a second side elevation view, and a top plan view, respectively, of the intervertebral prosthetic device and the drill guide ofFIG. 15A.
• FIGS. 16A-16D are a top perspective view, a first side elevation view, a second side elevation view, and a top plan view, respectively, of the drill guide ofFIG. 15A.
• FIG. 17A is a top perspective view of the intervertebral prosthetic device and the drill guide ofFIG. 15A, showing placement of anchor elements through the drill guide and a compressible member of the intervertebral prosthetic device;FIGS. 17B-17D are a first side elevation view, a second side elevation view, and a top plan view, respectively, of the intervertebral prosthetic device, including the anchor elements, and the drill guide ofFIG. 17A.
• FIG. 18A is a side elevation view of an intervertebral prosthetic device, including anchor elements, and a drill guide in accordance with another embodiment of the invention;FIGS. 18B-18D are a top perspective view, a side elevation view, and a top plan view, respectively, of the intervertebral prosthetic device, including the anchor elements, and the drill guide ofFIG. 18A.
• FIGS. 19A-19E are a top perspective view, a bottom plan view, a bottom perspective view, a first side elevation view, and a second side elevation view, respectively, of a plate of an embodiment of a fixation member in accordance with the invention.
• FIG. 20 is a sectional view of a vertebra, including a plate, as shown inFIGS. 19A-19E, implanted in the vertebra.
• FIG. 21A is a top perspective view of an intervertebral prosthetic device, including anchor elements and spacers, in accordance with another embodiment of the invention;FIGS. 21B-21D are a first side elevation view, a second side elevation view, and a top plan view, respectively, of the intervertebral prosthetic device, including the anchor elements and the spacers, ofFIG. 21A.
• FIG. 22A is a top perspective view of an intervertebral prosthetic device, including spacers, in accordance with another embodiment of the invention;FIGS. 22B-22D are a first side elevation view, a second side elevation view, and a top plan view, respectively, of the intervertebral prosthetic device, including the spacers, ofFIG. 21A.
• FIGS. 23A-23D are a top perspective view, a first side elevation view, a second side elevation view, and a top plan view, respectively, of a spacer.
• FIG. 24 is a front perspective view of another embodiment of an implantable prosthetic device; the device be shown in a break-away view of a spine.
• FIG. 25 is a top perspective view of the implantable device ofFIG. 24.
• FIG. 26 is a side perspective view of the implantable device ofFIG. 24.
• FIG. 27 is another side perspective view of the implantable device ofFIG. 24.
• FIG. 28 is a perspective view of the implantable device ofFIG. 24 having anchor elements therethrough.
• FIGS. 29A and 29B are respective cross-sectional and perspective views of an alternate embodiment compressible member;FIGS. 29C and 29D are respective cross-sectional and perspective views of another alternate embodiment compressible member; andFIG. 29E is a cross-sectional view of either of the embodiments shown inFIGS. 29A-29D implanted in an intervertebral disc.
• FIGS. 30A and 30B are cross-sectional views of another alternate embodiment compressible member in whichFIG. 30A shows the compressible member partial implanted andFIG. 30B shows the compressible member completely implanted;FIGS. 30C and 30D show an alternate embodiment plate that may be used in the embodiment shown inFIGS. 30A and 30B;
• FIG. 31 is a cross-sectional view of two compressible members implanted in intervertebral discs, one of which is another alternate embodiment compressible member.
• FIG. 32 is a cross-sectional view of alternate embodiment compressible member implanted in an intervertebral disc.
• FIGS. 33A and 33B are a top perspective view and a side elevation view (in cross section), respectively, of an endplate and nucleus cutter;FIG. 33C is a side elevation view, in cross section, of an alternative embodiment of the endplate and nucleus cutter.
• FIG. 34A is a side elevation view of a compressor that includes a pair of endplate and nucleus cutters andFIG. 34B is a side elevation view of a distractor that includes an endplate and nucleus cutter.
• FIG. 35 is a schematic view of a compressor with endplate and nucleus cutters inserted into the cavities of adjacent vertebral bodies.
• FIG. 36A is a schematic view of an alternative embodiment of the endplate and nucleus cutter in accordance with the invention;FIG. 36B is a bottom plan view of a main body of the endplate and nucleus cutter ofFIG. 36A;FIGS. 36C and 36D are a top perspective view and a bottom plan view, respectively, of the cutting surface of the endplate and nucleus cutter ofFIG. 36A; andFIG. 36E is a perspective view of another alternative embodiment of the endplate and nucleus cutter.
DETAILED DESCRIPTION
• Although the less invasive embodiment shown inFIG. 7 may not be as effective as the embodiment shown inFIG. 1 and/or may be subject to subsidence, the ability to implant a disc replacement prosthetic device via a hole formed in only one adjacent vertebral body is minimally invasive and is, therefore, advantageous. As a result, the question becomes: how can one replace one or more discs via one vertebral body hole while: (a) greatly reducing the likelihood of subsidence, (b) making the device adaptable to particular patients and/or to the particular disc being replaced; (c) ensuring that the device remains in proper position; (d) providing a straightforward method of implantation; (e) making it cost effective for the patient.
• The answer to one or more of the parts to this question lies in the prosthetic device embodiments disclosed herein. These prosthetic device embodiments are not only readily implantable via a hole in a single vertebral body, they are so implantable while: (a) reducing the likelihood subsidence by means of anchors and tabs which serve to fix the device to the cortical bone of the vertebral body; (b) being adaptable by means of various compressible member embodiments; (c) ensuring the device remains in position by being fixedly engaged with the vertebrae and by being encapsulated by the annulus fibrosis; (d) being implantable in a time frame which is no longer than current implantation surgery; and (e) being cost effective by means of being modular and adjustable. The various embodiments of this novel prosthetic device will now be described with reference to the drawings, wherein like numerals indicate like parts.
• Aprosthetic device200 that minimizes the likelihood that the device may subside in patients with osteopenic bone is shown inFIGS. 15A-15D and17A-17D. In certain patients having thin bones, the bone (labeled36,38 inFIG. 1, and labeled88 inFIG. 7) in areas adjacent to the implanted prosthetic device may be subject to being crushed and/or collapse under heavy loads. This condition also may occur in other patients after implantation of the prosthetic device, but before the bone graft has time to heal. To minimize subsidence, one or more anchor elements, such as pins, rods, or screws, can be threaded either through a fixation member or through the compressible member to fix the prosthetic device in the hard outer cortical bone of the vertebra in which the cavity was created for device implantation.
• The following description ofFIGS. 15A-15D and17A-17D relates to a prosthetic device embodiment having a compressible member and only one fixation member. However, it should be understood that the features described below can be applied to a prosthetic device having a fixation member on either side of the compressible member (as shown inFIGS. 21A-21D) or to a prosthetic device having two compressible members on either side of a fixation member (as shown inFIGS. 25-28).
• The one compressible member/one fixation member embodiment ofFIGS. 15A-15D,17A-17D is similar to the embodiment ofFIG. 7. However, whereas theFIG. 7 embodiment provides for a separate second fixation member, the embodiment ofFIGS. 15A-15D,17A-17D incorporates at least some of the functionality of the second fixation member into the compressible member, amongst other improvements as later described in detail.
• FIGS. 15A-15D and17A-17D show aprosthetic device200 having afixation member214 for fixation within a cavity of a first vertebral body, and acompressible member218 for implantation in the region of an excavated nucleus pulposus of an operative intervertebral disc. In this embodiment, thefixation member214 comprises an adjustable member having anouter plate250 and aninner plate252. Thecompressible member218 includes afirst plate242, asecond plate244, and one or more compressible elements. In the embodiment shown, the compressible elements are a plurality ofcoil springs240, positioned between theplates242,244. Adjacent plates of theadjustable fixation member214 and thecompressible member218 can be secured directly together. That is, aninner plate252 of thefixation member214 can include anangled protrusion253 that mates with anangled recess243 in thefirst plate242 of thecompressible member218 in the manner of a dovetail joint's tenon and mortise. Theangled portions253,243 secure thefixation member214 and thecompressible member218 together in a keyed fit, without need for other fasteners or fastening materials. It will be understood that, in an alternative embodiment, the angled protrusion can be formed on the first plate of the compressible member, and the angled recess can be formed in the inner plate of the fixation member.
• As previously mentioned, theprosthetic device200 is designed to minimize subsidence of thedevice200 into bone adjacent thedevice200 by employing anchor elements to secure thedevice200 into hard outer cortical bone. In the illustrated embodiment,plate244 of thecompressible member218 includesholes246 for receipt ofanchor elements310. A drill guide can be used to create holes through the cortical bone toward theholes246 in thedevice200.FIGS. 16A-16D show an embodiment of thedrill guide300. Thedrill guide300 includes an L-shapedbody302 having acurved face304 at one end and adrill positioning block306 at the other end. Thedrill positioning block306 can have one ormore drilling channels308. Thedrilling channels308 are configured to guide a drill bit through the bone toward theholes246 in theplate244 of thecompressible member218.
• As best seen inFIG. 15A, thedrill guide300 can temporarily engageprosthetic device200 to guide the drilling of holes through bone towardholes246 inprosthetic device200. Theguide300 subsequently facilitates placement of theanchor elements310 through theholes246, as best seen inFIG. 17A. To properly position thedrill guide300 relative toprosthetic device200, anupper portion301 of the L-shapedbody302 is pushed between twoadjustment elements224 of thefixation member214 such that thecurved face304 aligns with and engages athird adjustment element224 offixation member214, as shown inFIG. 15A. As theupper portion301 of the L-shapedbody302 has a width303 which is substantially equal to the distance between the twoadjustment elements224 through which it is pushed, when thecurved face304 meets thethird adjustment elements224, the threeadjustment elements224 substantially immobilize thedrill guide300 with respect to thedevice200.
• Other embodiments of the drill guide need not includecurved face304 and can be configured to mount to other portions of the prosthetic device. In addition, the L-shaped body of thedrill guide300 can be configured to be adjustable along each of the two legs that form the “L”. For example, each leg of the “L” can comprise telescoping elements to lengthen or shorten the leg, depending on the size of the prosthetic device and the position ofholes246 of thecompressible member218. Further, as an alternative to mounting thedrill guide300 to theprosthetic device200, theguide300 can be mounted to the outer vertebral body set to receivefixation member214. In addition, where it is inconvenient or undesirable to use adrill guide300, another technique, such as fluoroscopic imaging, may be used to determine drill placement. However, such a protocol may be less accurate.
• Once holes have been made in the bone,anchor elements310 can be inserted throughdrilling channels308, through the newly-drilled holes in the bone, and through theholes246 in thecompressible member218, as shown inFIGS. 17A-17D. Thedrill guide300 then can be removed from theprosthetic device200.
• Theanchor elements310 can comprises rods, screws, or any other suitable support structure. In addition, theanchor elements310 themselves can include small holes or irregularities on their surface, or they may have a bioreactive coating such as hydroxyapatite, to enhance fixation to the bone so that theanchor elements310 do not back out ofholes246.
• Although the figures show theanchor elements310 arranged parallel to each other, holes246 can be arranged so that theanchor elements310 diverge or converge. Appropriate holes can be drilled through the cortical bone by reconfiguringdrilling channels308 in thedrill positioning block306 to align with the converging/diverging holes in the prosthetic device. Alternatively, thedrill guide300 may be repositioned after drilling a first hole through the bone that is aligned with a first hole in the prosthetic device, and before drilling a second hole that is aligned with a second hole in the prosthetic device.
• In the embodiment ofFIGS. 17A-17D, theanchor elements310 are dimensioned to traverse the entire diameter of the vertebral body to obtain bi-cortical purchase, that is, fixation in the hard outer cortical bone on either side of the vertebral body. Alternatively, theanchor elements310 can be shortened so that they to traverse only part of the diameter of the vertebral body to obtain uni-cortical purchase, that is, fixation in the hard outer cortical bone on only one side of the vertebral body.
• Further, although theanchor elements310 are shown passing through thebottom plate244 of thecompressible member218, in alternative embodiments, the site for placement of theanchor elements310 can be through eitherplate250,252 of thefixation member214 or through theupper plate242 of thecompressible member218. Moreover, as shown inFIGS. 18A-18D, rather than passing through a portion of the prosthetic device, theanchor elements310 can pass under and adjacent the lowermost plate of the prosthetic device to minimize subsidence of the device into the cancellous subchondral bone in the central portion of the vertebral body.
• More specifically,FIGS. 18A-18D show an embodiment of aprosthetic device400 having afixation member414 and acompressible member418. Thecompressible member418 has abottom plate444, here shown with a convexlowermost surface445. The convexlowermost surface445 may be configured to sit within a correspondingly shaped concave seat2050 (shown inFIG. 24) formed in the cortical bone of an endplate of an adjacent vertebral body. Theanchor elements310 are positioned under and just adjacent to thislowermost surface445 to minimize subsidence of theprosthetic device400.
• In yet another aspect of the present invention, either or both of the plates of the fixation member can include a tab to help minimize subsidence of the prosthetic device.FIGS. 19A-19E show aplate500 for a fixation member that includes atab502 extending from the periphery of the generally circular, main portion of theplate500. Thetab502 is configured to rest on outer cortical bone of a vertebral body. In this regard,FIG. 20 is a sectional view through a vertebral body, illustrating aplate500 with atab502 extending into outercortical bone506 of thevertebral body504. Thetab502 inhibits the ability of the prosthetic device to sink into thecancellous bone508 of thevertebral body504.
• Theplate500 may also include ariser510 through which holes511, which are configured to receiveanchor elements310, can extend. In addition, a drill bit can be guided through theholes511 in theriser510 to drill holes through the bone of the vertebral body, thereby eliminating the need fordrill guide300. Althoughplate500 is shown inFIGS. 19A-19E and22 with both atab502 and ariser510 withholes511 foranchor elements310, it will be understood that other embodiments of the plate can include only a tab, such as inFIG. 22A, or can include holes to receiveanchor elements310 but lack a tab.
• Anotherprosthetic device embodiment700 that incorporates fixation plates likefixation plate500 in embodiment shown inFIGS. 19A-19E is shown inFIGS. 21A-21D. Thisprosthetic device700 has first andsecond fixation members714,716 and acompressible member818. Thefixation members714,716 each include afixation plate750 on their outer ends; theplates750 havetabs751 extending therefrom. When theprosthetic device700 is implanted in upper and lower vertebral bodies, thetabs751 rest on the outer cortical bone of the vertebral bodies.Anchor elements310 may extend through the cortical bone of the vertebral bodies and throughholes713 formed in thetabs751, to enhance the stability of theprosthetic device700.
• In yet a further aspect of the present invention, the prosthetic device can includespacers620 to maintain thefixation members714 at a desired elongated position. Thespacers620 can be used in lieu of the lock screws63 seen inFIG. 4 and their aforementioned alternatives.FIGS. 23A-23D show an embodiment of aspacer620 that can be used withfixation members714. Thespacer620 has afirst box portion622, asecond box portion624, and apeg626 projecting from thefirst box portion622.
• In a prosthetic device employing aspacer620 as shown inFIGS. 21A-21 D, theinner plate752 of thefixation member714 can have anotch754, and eachplate842,844 of the compressible member can have a well846. Thepeg626 of thespacer620 is configured to pass through thenotch754 and snap into the well846, to lock thespacer620 in place in a snap fit, as shown inFIG. 21A. When thepeg626 of thespacer620 is locked in theappropriate plate842,844, thesecond box portion624 resides between theadjustment elements724 of thefixation member714, as shown inFIG. 21B. Thespacers620 may be configured in varying shapes and of various heights to accommodate different sized vertebrae.
• Thespacers620 can be positioned infixation members714 after thefixation members714 are properly positioned in the vertebral bodies. That is, once thefixation members714 are positioned in the vertebral bodies, the tension or load experienced by thecompressible member818 needs to be adjusted to optimize the normal loading and compression (i.e., the functionality) of the particular disc being replaced.
• To optimize the normal loading and compression, a surgeon can use a tensioner, (such as the tensioner described in U.S. Pat. No. 6,761,723) to move theplates750,752 of thefixation member714 toward the endplates of the vertebral body. In this manner, the tensioner may be used to elongate thefixation member714 until a proper elongation distance between theplates750,752 is achieved. As thefixation member714 elongates,plate752 contacts and encounters resistance from thecompressible member818. The surgeon can continue to apply a load via the tensioner to thefixation member714 until a desired corresponding reactive load from thecompressible member818 is reached.
• When the applied load measured by the tensioner equals the desired load, the surgeon knows that thefixation member714 has been lengthened or elongated an appropriate amount to place thecompressible member818 under the proper degree of tension. At this point, thespacer620 can be inserted into thefixation member714 until thepeg626 of thespacer620 snaps in thewell846. As a result, thespacer60 maintains thefixation member714 at the appropriate length. The tensioner then can be removed from thefixation member714.
• As an alternative to thespacer620, thestruts224 can be configured for adjustment like a crutch, that is, by having a hole through an outer casing and a plurality of holes through an adjustable inner member. When the inner member is adjusted to the proper height, a fastener can be inserted through the hole in one side of the casing, through the corresponding hole in the inner member, and then through the hole in the other side of the casing. The fastener immobilizes the inner member with respect to the casing and maintains the proper elongation distance between the upper andlower plates250,252 of thefixation member214.
• Clamps also can be used to maintain the proper elongation distance between theplates250,252. The clamps can be C-shaped in cross section and have a length equal to the elongation distance. The C-shaped cross section of the clamps leaves a slit or opening along their length. The clamps also are resiliently flexible. When the slit of a clamp is pressed against a strut, the slit widens so that the clamp can be slid around the strut. Once around the strut, the clamp returns to its initial shape. The clamps thus can be positioned on thestruts224 to substantially surround thestruts224 and maintain the proper elongation distance between theplates250,252.
• A tripod also can be used to maintain the proper distance between theplates250,252. The surgeon can select a tripod of an appropriate height, that is, of a height equal to the desired elongation distance, and slide it into thefixation member214. The surgeon then can position the legs of the tripod on thelower plate252, preferably against threestruts224, and position the top of the tripod against theupper plate250.
• FIGS. 22A-22D show another embodiment of theprosthetic device700′. Thisprosthetic device700′ is similar to theprosthetic device700 ofFIGS. 21A-21D, except that theouter plates750′ of thefixation members714′ of thedevice700′ shown inFIGS. 22A-22D do not include therisers753 present on theouter plates750 of thefixation members714 of thedevice700 shown inFIGS. 21A-21D. All other elements of thefixation members714′,716′ of thedevice700′ shown inFIGS. 22A-22D are the same as the corresponding elements of thefixation members714,716 of thedevice700 shown inFIGS. 21A-21D and, therefore, are similarly numbered but include a differentiating apostrophe.
• Another prosthetic device embodiment, which is shown inFIG. 24, restores normal biomechanics and motion of a pair of failing, adjacent intervertebral discs. Theprosthetic device2000 is designed to spare the annulus fibrosis of the discs and the anterior longitudinal ligament of the spine. Moreover, the prosthetic device ensures solid bone fixation via attachment to cancellous vertebral body bone, rather than to the external surface of non-uniform and/or sclerotic vertebral body endplates.
• Theprosthetic device2000 may be implanted and adjusted in a procedure that should not take longer than current spinal fusion procedures. Further, it will be understood from the following description that in conjunction with the previously described embodiments, due to its somewhat modular construction, the prosthetic device can be modified to replace more than two intervertebral discs by including an appropriate number of fixation members and compressible members, as needed. A related embodiment of the invention (later discussed in detail) addresses a method of spinal prosthetic implantation by which one or more intervertebral discs may be replaced by an implantable prosthetic device.
• Theprosthetic device2000 includes first and secondcompressible members2020 and afixation member2030 sized to fit within a cavity in thevertebral body2130 between the firstcompressible member2020 and the secondcompressible member2020. The firstcompressible member2020 is sized to substantially replace the nucleus pulposus of a firstintervertebral disc2120. Similarly, the secondcompressible member2020 is sized to substantially replace the nucleus pulposus of a secondintervertebral disc2140 that is separated from the firstintervertebral disc2120 by thevertebral body2130. In the embodiment shown, the secondcompressible member2020 has the same structure as the firstcompressible member2020.
• Eachcompressible member2020 comprises a compressible body portion formed of one or morecompressible bodies2022. Thecompressible bodies2022 may be made of a biocompatible material compressible in an axial direction (i.e., in a direction substantially parallel to the spine).
• Thecompressible members2020 include afirst plate2024 proximal to thefixation member2030 and asecond plate2026 distal from the fixation member. Thesecond plates2026 may havesections2027 havingconvex surfaces2028, which may serve as and function like the second fixation member shown inFIG. 7. Further, as later explained in detail, theconvex surfaces2028 may be sized to sit within correspondingly shapedconcave seats2050 formed in the cortical bone endplates of vertebral bodies.
• Thefixation member2030 may include one ormore adjustment members2038 and/or a locking mechanism, as best shown inFIGS. 26 and 27. Theadjustment members2038 may be telescoping struts, the length of which may be fixed by a locking mechanism such as the c-shaped clamps, tripods, spacers, or other suitable extension devices, as previously discussed. By fixing the height of thefixation member2030, the locking mechanism fixes the load applied to thefixation member2030.
• Similar to the embodiments previously discussed with respect toFIGS. 15-21, thefixation member2030 additionally comprises afirst plate2032 and asecond plate2034. The first andsecond plates2032,2034 are configured to engage thefirst plates2024 of thecompressible members2020, in a dovetail tenon/mortise relationship. Specifically, as shown inFIGS. 24 and 25, thefirst plates2024 haveprojections2027 which are sized to engage correspondingly shapedslots2039 formed in the first andsecond plates2032,2034 of thefixation member2030. Thefixation member2030 engages thecompressible members2020 by sliding theslots2039 formed in the first andsecond plates2032,2034 of thefixation member2030 onto the adjacent correspondingly shapedprojections2027 formed on thefirst plate2024 of thecompressible members2020.
• If only one intervertebral disc needs to be replaced, thesecond plate2034 of thefixation device2030 can rest against an interior side of the subchondral bone of the endplate of a vertebral body adjacent the failing disc. In this instance, thefixation member2030 would be positioned in a vertebral body adjacent the failing disc and thecompressible member2020 would be positioned in a failing disc. Thesecond plate2026 of thecompressible member2020 may sit within aseat2050 formed in the cortical bone of the vertebral body above the disc.
• Similar to the aforementioned embodiments, to reduce the risk of subsidence, thecompressible members2020 may includedrilling channels2029 through thesecond plates2026. Thedrilling channels2029 may be configured to receive anchor elements2160 (e.g., screws, other fasteners, plates, etc.), as shown inFIG. 28. Theanchor elements2160 may be journalled through thedrilling channels2029 and into the cortical bone of a vertebral body, in the manner previously discussed. As a result, the orientation of thecompressible members2020 with respect to the vertebral body may be additionally stabilized. In addition, either plate of thefixation member2030 and either plate of thecompressible members2020 can include a tab, as previously discussed, to help minimize subsidence of the prosthetic device.
• To implant theprosthetic device2000, a cavity is created in the vertebral body between the two discs to be reconstructed, in the manner previously described. This procedure, which involves excising bone matter from the vertebral body, can be performed using a cutting guide, a chisel and a chisel guide, and a reamer (such as those described in U.S. Pat. No. 6,761,723) and/or using surgical implements discussed herein with respect toFIGS. 33-36. Bone harvested from the vertebral body by the reamer can be used after implantation of the prosthetic device to promote bone ingrowth into the prosthetic device, as previously described. This procedure creates a cavity bounded by subchondral bone of the endplates of the vertebral body.
• Once the cavity in the vertebral body is formed, an endplate and nucleus cutter attached, for example, to a-distractor920 (shown inFIG. 34B), may be used to cut (which may be in the form of boring) through the first endplate of the vertebral body adjacent the first failing intervertebral disc to be replaced. Once through the endplate, the cutting can continue through the nucleus pulposus of the first failing disc to excise the nucleus pulposus thereof, creating a cavity for acompressible member2020. In this method, the annulus fibrosis is maintained, although it is envisioned that, if the cutting inadvertently cuts into an inner portion of the annulus fibrosis, the annulus fibrosis still may be capable of securely retaining thecompressible member2020. Additional cutting may be performed into the endplate of the vertebral body on the other side of the first failing intervertebral disc, thereby forming aseat2050 against which aconvex surface2028 of thecompressible member2020 may be positioned. Theseat2050 will be generally concave in shape so as to better engage theconvex surface2028 of thecompressible member2020.
• Once the nucleus pulposus of the first failing intervertebral disc has been excised and theseat2050 has been formed, the same process may be used to bore through the other endplate of the vertebral body in which the cavity was formed and through the nucleus pulposus of the second failing disc adjacent it. Further, aseat2050 may be formed in the vertebral body on the other side of the second failing disc.
• Once cutting is completed, a firstcompressible member2020 is positioned in the cavity in the vertebral body and then pushed through the hole in the endplate and into the space left by the excised nucleus of the first failing disc.
• As the firstcompressible member2020 is inserted into the first failing disc, theconvex surface2028 is pushed into theseat2050 in the vertebral body endplate on the other side of the disc. Although theconvex surface2028 may be positioned in cancellous bone in the interior of a vertebral body, it is preferably position in the cortical bone, to help minimize the risk that thesecond plate2026 will, over time, undesirably creep into the vertebral body as a result of loading.
• Once the firstcompressible member2020 is fully implanted, a secondcompressible member2020 is inserted into the second failing intervertebral disc in the same manner. Similarly, theconvex surface2028 of the secondcompressible member2020 is inserted into theseat2050 adjacent the second failing disc. It should be readily recognized that the order in which thecompressible members2020 are inserted can be reversed.
• Once thecompressible members2020 are in place, the surgeon slides afixation member2030 into the cavity in the vertebral body while engaging theprojections2027 of thecompressible members2020 and theslots2039 in the first andsecond plates2032,2034 of thefixation member2030. As a result, thefixation member2030 is fixedly joined to thecompressible members2020. In other embodiments, thecompressible members2020 and thefixation member2030 may be connected by conventional attachment members, such as screws, or by biocompatible cement or a suitable adhesive composition.
• When thefixation member2030 is in place, the length of theadjustment members2038 can be adjusted to fix the length of thefixation member2030, in the manner previously described. Similarly, the length of thefixation member2030 can be maintained by using a locking mechanism, such asspacer2036, which prevents further inward adjustment of theadjustment members2038, as previously described. Alternatively, fixation members can be available in a variety of fixed sizes; a properly sized fixation member could be selected for implantation in the cavity of the vertebral body, thereby negating the need for a locking mechanism. Regardless, when the length of thefixation member2030 is fixed, the cavity in the vertebral body may be filled with bone graft, as previously described.
• To reduce the risk of subsidence, thecompressible members2020 and/or thefixation member2030 may havedrilling channels2029 for receiving anchor elements2160 (e.g., screws) to supplement immediate fixation during healing of the bone graft, as previously described.
• A porous bone ingrowth coating and/or surface texturing may also be applied to the device. For example, hydroxyapatite or other bone-to-implant chemical or biological interface surface treatment may be applied to the first andsecond plates2032,2034 of thefixation member2030 and/or to the convex surfaces2028 (each of which is in contact with bone), to enhance bone growth into a textured porous surface.
• If either of the vertebral bodies adjacent thecompressible members20 are scoliotic, thecompressible elements2022 used in thecompressible members2020 may be designed to combat this problem. Specifically, the selectedcompressible elements2022 may have spring constants which are greater or less than the spring constants of the remainingcompressible elements2022. As a result, corrective loading on the scoliotic bodies can be better achieved.
• Unlike conventional implanted prosthetic devices, which are typically not recommended for replacing two discs, thisprosthetic device embodiment2000 easily replaces the nucleus pulposuses of the intervertebral discs both above and below a vertebral body. Further, not only is this approach more efficient for surgeons, it avoids the problems inherent in separately distracting two disc spaces sufficiently to insert total disc replacements.
• Various intervertebral disc prosthetic device embodiments (and the methods of implanting them) have been described. In conjunction with these embodiments, however, various modifications may be used to address a particular patient's condition and/or the level in the spine in which the device will be implanted (e.g., between Lumbar-5 and Sacrum-1 there is a great variation among patients in the shape of the joint). Accordingly, the following describes various alternative compressible member embodiments which may be employed with any of the aforementioned prosthetic device embodiments.
• FIGS. 29A-29E show two alternate embodiments for a compressible member. Specifically,FIGS. 29A and 29B respectively show a cross-sectional view and a perspective view of acompressible member2100 andFIG. 29E shows thecompressible member2100 positioned in a disc.
• Thecompressible member2100 is formed of abase member2102 that may, as shown, be in the shape of a cup. Thelower surface2112 of thebase member2102 may be attached to a fixation member (not shown inFIGS. 29A-29E) in any manner previously discussed (e.g., screws, dovetail tenon/mortise joint, etc.)
• Acircumferential wall2114 of thebase member2102, which rises upward from thelower surface2112, encloses a plurality of compressible elements2104 (e.g., springs, or any other compressible element previously discussed). As shown inFIG. 29E, thewall2114, when implanted, compensates for anatomic variations and assures that theendplate2122 of thevertebral body2120 engages solid metal.
• The other ends of thecompressible elements2104 are attached to anupper member2106, in a manner similar to the previously described compressible member embodiments. Similarly, theupper member2106 may have aconvex surface2108 which is configured to rest within a seat2050 (shown inFIG. 24) formed in a vertebral body endplate, as previously discussed.
• Thecompressible member embodiment2100′ shown inFIGS. 29C-29D is substantially similar to thecompressible member embodiment2100 shown inFIGS. 29A-29B, except that thewall2114 in thebase member2102 in the embodiment shown inFIGS. 29A-29B is replaced with a slottedwall2114′ defining analternative base member2102′.
• The reason for the slottedwall2114′ is that for some individuals and/or some disc locations, additional clearance may serve to facilitate placing the springs over as wide an area as possible. However, as the slots reduce the support and attachment to the cortical bone of the vertebral body, the desires to use certain spring designs and to enhance support/attachment must be weighed in each particular instance.
• Anothercompressible member2200 embodiment is shown inFIGS. 30A-30B. Thecompressible member2200 includes abase member2202,compressible elements2204, and anupper member2206. In this embodiment, thebase member2202 is wider than the diameter of thehole2210 but narrow enough so that it can go through thehole2210 at an angle after which it can be maneuvered so as to cover thehole2210, as shown inFIG. 30B. In either case, thebase member2202 rests against the cortical bone of thevertebral body2220, thereby reducing the likelihood that thecompressible member2200 may experience subsidence into thevertebral body2220 as a result of cyclical loads applied to thecompressible member2200.
• Anothercompressible member2200′ embodiment is shown inFIGS. 30C and 30D. In this embodiment, thebase member2202′ is expandable to be wider than the diameter of thehole2210 in a vertebral body endplate through which thecompressible member2200′ is implanted. Specifically, thebase member2202′ includes arotatable driving plate2240 and a plurality of radiallyadjustable leaves2250. The rotatable plate includes a plurality ofprojections2242 that, when therotatable plate2240 rotates, push theleaves2250 radially outward alongrails2260, thereby radially adjusting the overall diameter of thebase member2202′. As a result, after thecompressible member2200′ is pushed through thehole2210, thebase member2202′ may be radially expanded to fix thebase member2202′ in a manner similar to that shown inFIG. 30B. In addition, although the size ofbase member2202′ is described as being adjusted by means of leaves, the embodiment is not so limited. Rather, the base member could be adjusted in other ways such as, for example, by means of screws, telescoping rods, etc.
• Anothercompressible member2400 embodiment is shown inFIG. 31. A firstcompressible member2300, which is provided in a first disc, abuts (along a concave seat2050) a firstvertebral body2430 and is connected to afixation member2440. This firstcompressible member2300 and thefixation member2440 may be any of the compressible member embodiments and fixation member embodiments, respectively, previously discussed. However, it is a secondcompressible member2400, which is also connected to thefixation member2440, which is the focus ofFIG. 31. Moreover, although the secondcompressible member2400 is shown as being part of a dual compressible member device, it should readily be recognized that it could be incorporated in a single compressible member device.
• The secondcompressible member2400, like previous embodiments, includes abase member2402 supporting a plurality ofcompressible elements2404. The other ends of thecompressible elements2404 are connected to anotherplate2406. Whereas in previous embodiments, theplate2406 would rest against a vertebral body, in this embodiment, theplate2406 is attached to a ball-and-socket joint comprised of asocket2408 and aball2410. Thesocket2408 is attached to theplate2406 and theball2410 is immobilized in thevertebral body2460 by means of aspike2412 or screw.
• The purpose of the ball-and-socket connection is to accommodate anatomic variation in which the angle between vertebral endplates may be highly variable among patients. This is particularly helpful between Lumbar-5 and Sacrum-1 where there is a great variation among patients in the shape of the joint and where replacement of two discs (as shown inFIG. 31) in this area is particularly complicated.
• It should be readily recognized that thecompressible member embodiments2300,2400 shown inFIG. 31 can be switched. In other words, thecompressible member embodiment2300 currently adjacent the uppervertebral body2430 can be switched with thecompressible member embodiment2400 currently adjacent the lowervertebral body2460.
• FIG. 32 shows another embodiment of acompressible member2500, which like theembodiment2400 shown inFIG. 31 employs aspike2512 to immobilize aplate2506, as hereafter explained in detail. Thecompressible member embodiment2500, like previous embodiments, has abase member2502, anupper member2506, and a plurality ofcompressible elements2504 which extend between thebase member2502 and theupper member2506.
• Whereas in many of the previously described embodiments, the end of a compressible member away from a fixation member was formed to have a convex surface configured to engage aconcave seat2050 formed in a vertebral body, in some instances such an engagement may not provide adequate support for the compressible member. As a result, in thecompressible member embodiment2500 shown inFIG. 32, theplate2506 adjacent thevertebral body2520 is formed with aspike2512 that is configured to penetrate into thevertebral body2520 so as to immobilize theplate2506 with respect to thevertebral body2520. Moreover, the likelihood of subsidence of thecompressible member2500 into thevertebral body2520 is slight as a result of the remainder of theplate2506 abutting the cortical bone endplate of thevertebral body2520.
• The aforementioned described various implantable prosthetic devices and the methods by which they may be implanted. In conjunction with these devices and their methods of implantation, this invention also addresses various tools by which the implantation methods may be performed.
• FIGS. 33A-33C illustrate a surgical implement, that is, a cutting implement that can be mounted to a compressor900 (shown inFIG. 34A) or a distractor910 (shown inFIG. 34B) to cut through an endplate of a vertebral body and the nucleus pulposus of the intervertebral disc adjacent the vertebral body. The exemplary cutting implement is in the form of an endplate andnucleus cutter920 having a substantiallycircular sidewall921 that terminates in acutting edge922.
• The maximum diameter of thesidewall921 of the endplate andnucleus cutter920 should not be greater than the minimum diameter of the nucleus pulposus and/or the diameter of the prosthesis to be implanted. In addition, thecutting edge922 can be smooth or, alternatively, serrated. Thecutting edge922 may be thinner than thesidewall921 and may be tapered to a sharp end. The endplate andnucleus cutter920 optionally can have aprojection923, as shown inFIG. 33B. The tip of theprojection923 can be used to create a notch in an endplate, thereby bracing the endplate andnucleus cutter920 relative to the endplate; theprojection923 can serve as an axis of rotation. Moreover, this bracing effect enables a surgeon to cut through the endplate with the sharp end of the endplate andnucleus cutter920, without risk that the endplate andnucleus cutter920 will inadvertently slide from its proper position relative to the endplate surface.
• An alternative embodiment of the endplate andnucleus cutter920′ is shown inFIG. 33C. The only difference between this embodiment and the one shown inFIG. 33B is that theprojection923′ is cylindrical in shape and has a concave end. An advantage of employing the embodiment ofFIG. 33C with the embodiment ofFIG. 33B on asingle compressor900 is that when the sharp edges of the two endplate andnucleus cutters920 approach each other, the tip of theprojection923 on thefirst cutter920 will be partially journalled into the concave end portion of theprojection923′ of thesecond cutter920′.
• As shown inFIG. 34A, an endplate andnucleus cutter920 can be attached to anend portion901 of afirst arm902 of thecompressor900 to face asecond arm904. Similarly, an endplate andnucleus cutter920, which is attached to anend portion903 of thesecond arm904, faces toward thefirst arm902 and toward the other endplate andnucleus cutter920.
• When thehandle905 of thecompressor900 is compressed, the first andsecond arms902,904 move toward each other. In addition, as the first andsecond arms902,904 move toward each other, they maintain their approximately parallel orientation, and the endplate andnucleus cutters920 approach each other. The endplate andnucleus cutters920 on the first andsecond arms902,904 can share a common central axis so that, when thehandle905 is fully compressed, the cuttingedges922 of the endplate andnucleus cutters920 contact each other.
• The endplate andnucleus cutters920 can be either fixedly mounted or rotatably mounted to thearms902,904 of thecompressor900. When the endplate andnucleus cutters920 are fixedly mounted, the surgeon can manually rotate thecutters920 by swinging thehandle905 of thecompressor900 side-to-side. This side-to-side motion, combined with compression of thehandle905, enables the cuttingedges922 to cut through the endplate and nucleus pulposus of the damaged disc. Alternatively, the endplate andnucleus cutters920 may be rotatably mounted to thecompressor900. A motor or other drive source can be connected to thecutters920 to rotate them relative to thearms902,904 of thecompressor900.
• Thecompressor900 can be used when a surgeon wants to implant a prosthetic device having two fixation members, one of which is to go into a vertebral body above a problematic disc and the other of which is to go into the vertebral body below the problematic disc.FIG. 35 shows acompressor900 being inserted into adjacent vertebral bodies to remove the nucleus pulposus of a damaged disc.
• In some situations, however, the surgeon needs to implant only one fixation member (e.g., the embodiments shown inFIGS. 15-18 and24-28) or only one non-extendable fixation member coupled to a compressible member (e.g., the embodiment shown inFIG. 7). In such situations, adistractor910 with only one, outwardly facing endplate andnucleus cutter920 may be used.
• FIG. 34B shows adistractor910 having one endplate andnucleus cutter920 on afirst arm912 which faces outward and away from asecond arm914. An outwardly facingplate930 is rotatably attached to thesecond arm914 by anaxle931. Theplate930 is designed to be placed against an endplate in a vertebral body and to remain immobile relative to the vertebral body.
• As the endplate andnucleus cutter920 of thedistractor910 either is manually rotated by the surgeon (in an embodiment where the endplate andnucleus cutter920 is fixedly mounted to the distractor500) or rotates as a result of a motor (in an embodiment where the endplate andnucleus cutter920 is rotatably mounted to the distractor910), the endplate andnucleus cutter920 will cut through one endplate in a vertebral body, while theplate930 remains pressed against the other endplate in the vertebral body. Theplate930 will not abrade the vertebral body against which it is placed because it does not rotate with respect to that endplate.
• When thearms912,914 of thedistractor910 are inserted into a cavity in a vertebral body and thehandle915 is subsequently compressed, theplate930 will move in one direction to contact the endplate of the vertebral body, and the endplate andnucleus cutter920 will move in an opposite direction to contact the other endplate of the vertebral body. Continued compression of thehandle915 and rotation of the endplate andnucleus cutter920 will force thecutter920 through the endplate and the nucleus pulposus of the adjacent intervertebral disc.
• It will be understood that an endplate andnucleus cutter920 can be mounted to devices having a configuration different than thecompressor900 anddistractor910. For example, an endplate andnucleus cutter920 can be attached to an end of a single arm, and a surgeon can grip the opposite end of the single arm to position the endplate andnucleus cutter920 appropriately to cut through the endplate and the nucleus pulposus of a damaged disc. The single arm can be bent to provide additional leverage.
• FIGS. 36A-36D illustrate another embodiment of an endplate andnucleus cutter1000. Thiscutter1000 includes arotating axle1002 withmultiple arms1004, a cylindricalmain body1006 with a pair ofoblique slots1008 to receive thearms1004 of theaxle1002, and acutting surface1010 that attaches to the cylindricalmain body1006. Thecutting surface1010 can have a flat profile or it can have a convex, domed profile as seen inFIGS. 36A, 36C, and36D. Thecutting surface1010 includes cuttingedges1012 that enable thecutter1000, when rotated, to cut through the endplate and the nucleus pulposus of the disc.
• In another embodiment shown inFIG. 36E, aserrated cutting edge1010′ can be defined around a perimeter of a cup-shapedcutter1000′ which is similar in shaped to the endplate andnucleus cutter920 shown inFIGS. 33A and 33B.
• Thecutter1000 can be mounted to the arm of a compressor or a distractor and, once positioned at a cutting location in a vertebral body, can elongate and move away from the arm. Accordingly, thecutter1000 can be placed through a relatively small vertebral body window and still reach all the way through the vertebral body endplate and the nucleus pulposus of the damaged disc. When thecutter1000 is in the shortened position, thearms1004 of theaxle1002 are positioned in theslots1008 at a location close to thecutting surface1010. With rotation of theaxle1002, friction forces thearms1004 to slide up theslots1008, which in turn elongates thecutter1000 and moves thecutting surface1010 toward the area to be cut.
• The intervertebral prosthetic device embodiments of the present invention offer several advantages. For example, the intervertebral prosthetic device embodiments replicate the mechanical properties of a natural intervertebral disc. The intervertebral prosthetic device embodiments restore disc height, defined as the axial distance between vertebrae adjacent the damaged disc, and duplicate the range of motion of a natural intervertebral joint.
• As the prosthetic device embodiments have no ball bearings (with the exception of the ball-and-socket joint of the embodiments shown inFIG. 31), rollers, or hinges, the intervertebral prosthetic device embodiments suffer minimal degradation of the prosthetic material and produce minimal wear debris under long-term cyclic loading conditions. Further, the prosthetic device embodiments: (a) can axially compress and thus dissipate energy; (b) may be easily repaired or replaced; (c) may be easily manufactured and implanted by a surgeon; and (d) are durable and modular. Moreover, as the prosthetic device embodiments need not include plastic polymers or elastomeric components, the prosthetic device embodiments do not degrade under long-term cyclic loading conditions.
• It should be understood that the benefit of the implantation procedure for the one compressible member/one fixation member embodiment and the dual compressible member/one fixation member embodiments is that only one vertebral body cavity is formed. As a result, both the time necessary for the implantation procedure and the amount of resultant healing are greatly reduced.
• Although the previously described embodiments of the intervertebral prosthetic device include an adjustable fixation member, it will be understood that the intervertebral prosthetic device can include a rigid fixation member sized specifically to fit the vertebral body and to adequately pretension the compressible member. Rigid fixation members can be made in various sizes so that a surgeon can select an appropriately sized fixation member for the particular surgical site.
• The prosthetic device embodiments can comprise biocompatible metallic materials, such as a titanium alloy having, for example, 4% vanadium and 6% aluminum. Persons of skill in the art will recognize other suitable materials, for example, a cobalt-chromium alloy, such asalloy number 301. Alternatively, the prosthetic device embodiments, with the exception of the springs of the compressible member, can comprise a ceramic material, such as aluminum oxide or zirconium oxide. The porous surfaces of the fixation members can be coated with hydroxyapatite or bioactive proteins (e.g., bone morphogenic protein) to encourage bone ingrowth.
• The fixation members of the prosthetic device embodiments, which may be composed of carbon fiber polyetheretherketone, bone graft (auto- or allo-graft bone), bone cement, etc., support the compressible member(s) until the bone graft (which is packed into the open space of the fixation members) heals. Once the bone graft heals, however, the fixation members may no longer be needed. Accordingly, the fixation members of the prosthetic device embodiments may be composed of a bioresorbable material that would gradually be replaced by bone over time. Suitable bioresorbable materials to form the fixation members include structural allograft (bank) bone, or polymers made of polylactic acid or polyglycolic acid. Similarly, the anchor members also can be made of carbon fiber or of a bioresorbable material, such as polylactic acid, polyglycolic acid, or a combination of those materials.
• The compressible members may be, for example, springs, elastomers, monolithic bodies, elastic polymers, hydrogels, disc allograft, or any other material which displays similar mechanical properties when placed under stress (i.e., tension and/or compression) and which substantially regains its original shape upon removal of the stress.
• The embodiments of the prosthetic device previously described have advantages over conventional devices. For example, although the prosthetic device may be implanted using a straight anterior approach, it may be implanted using an anterolateral approach to the spine that is a retroperitoneal approach in the plane between the abdominal vessels and the psoas muscle.
• Unlike the conventional and more dangerous straight anterior approach required by total disc replacement devices (which sever the anterior longitudinal ligament and/or sever the annulus fibrosis, both of which disrupt tissues that will not heal), the embodiments described herein only disrupt bone material in the adjacent vertebral body and the nucleus pulposus in the intervertebral disc. The bone heals and the nucleus pulposus is replaced by the prosthetic device.
• Further, the embodiments of the prosthetic device described herein minimally infringe upon areas of the vertebral body which would be used to provide a fusion should that later become necessary. Specifically, by maintaining the anterior longitudinal ligament, the anterolateral approach helps maintain spinal function and stability. In addition, an anterolateral approach on one side of a vertebral body allows for a later opposite side approach for adjustment of the device or for adjacent level disc replacement should that become necessary. Further, this opposite side approach would not be hindered by scar tissue from the previous procedure.
• The prosthetic device embodiments also allow for bending and torsion motion, as well as axial displacement and elastic compression. Further, unlike an articulated joint, the prosthetic device deforms similarly to a normal, healthy disc. Moreover, unlike previous total disc replacement devices which may result in motion of about 3.8° to 4.6°, the embodiments of the invention herein described maintain the motion at a nearly healthy level of motion, i.e., about 7° to about 12°.
• The ability to pretension the fixation member allows for a more precise restoration of disc height. Further, as the fixation members may be anchored entirely to cancellous bone, at least some embodiments avoid problems inherent to poor bony ingrowth, which may result from sclerotic endplates. As a result, the risk of device loosening is minimized. And, as the device is enclosed entirely by bone and the annulus fibrosis, ejection, dislocation, and migration of the device is very unlikely. In addition, intramedullary fixation of the fixation member in the vertebral body provides greater stability. The fixation member is provided within the cancellous bone of a vertebral body adjacent the failing disc(s), to maximize the osteogenic potential of bone to grow into the fixation member. Further, the replacement of the autologous bone removed from the vertebral body during the procedure (or the addition of bone cement) into the open vertebral body facilitates the transfer of loads to the cortical bone walls of the vertebral body once the bone heals.
• Moreover, fibrous soft tissue growth into the compressible members will fill the normal volume of the disc nucleus. As a result, as the compressible member is compressed, this tissue will bulge outward and radially load the inner annulus fibrosis in a manner similar to a healthy nucleus. The radially outward loading will restore the function of the retained annulus fibrosis.
• Finally, the prosthetic device embodiments may be used no matter how collapsed a patient's disc may be. An overdistraction problem inherent for installation of total disc replacements does not arise with respect to the prosthetic device described herein.
• The preferred embodiments have been set forth herein for the purpose of illustration. This description, however, should not be deemed to be a limitation on the scope of the invention. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices, shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims (57)

1. A prosthetic device comprising:

a first compressible member sized to substantially replace the nucleus pulposus of a first intervertebral disc;

a second compressible member sized to substantially replace the nucleus pulposus of a second intervertebral disc that is separated from the first intervertebral disc by a vertebral body; and

a fixation member sized to fit within a cavity in the vertebral body between the first and second compressible members.

2. The prosthetic device according toclaim 1, wherein the fixation member comprises:

at least one adjustable member configured to adjust a length of the fixation member; and

a locking mechanism configured to maintain the adjustable member at a fixed length.

3. The prosthetic device according toclaim 2, wherein the locking mechanism is a spacer.

4. The prosthetic device according toclaim 1, wherein each of the first and second compressible members comprises at least one of a spring, an elastomer, and disc allograft.

5. The prosthetic device according toclaim 1, wherein a plate of each of the first and second compressible members is configured to be positioned within a seat formed in an endplate of the vertebral body adjacent thereto.

6. A prosthetic device comprising:

a fixation member sized to fit within a cavity in a first vertebral body; and

a compressible member sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body,

wherein:

(A) a first side of the compressible member is configured to engage the fixation member and a second side of the compressible member is configured to engage a second vertebral body, and

(B) the second side of the compressible member is configured to fit within a seat formed in the cortical bone of the endplate of the second vertebral body.

7. An intervertebral prosthetic device for implantation in a spine, comprising:

a rigid fixation member having a fixed length, the rigid fixation member being configured to be placed in a cavity of a vertebral body and against bone of the vertebral body; and

a first compressible member configured to be placed in a cavity in a first intervertebral disc adjacent the vertebral body and to be secured to the rigid fixation member,

wherein:

(A) the compressible member is constructed to remain compressible after implantation and has at least one compressible element that remains compressible after implantation, and

(B) the rigid fixation member is sized to compress the compressible member a predetermined amount when the rigid fixation member and the first compressible member are placed in the cavity in the first vertebral body and in the cavity in the first intervertebral disc, respectively.

8. The intervertebral prosthetic device according toclaim 7, further comprising:

a second compressible member,

wherein the second compressible member is configured to be:

(A) placed in a cavity in a second intervertebral disc adjacent the vertebral body on the opposite side as the first intervertebral disc; and

(B) secured to the rigid fixation member.

9. The intervertebral prosthetic device according toclaim 8, wherein the first and second compressible members are sized to replace the nucleus pulposuses of the first and second intervertebral discs, respectively.

10. The intervertebral prosthetic device according toclaim 7, wherein the rigid fixation member is composed of a bioresorbable material.

11. The intervertebral prosthetic device according toclaim 7, wherein the first compressible member has a plate opposite the rigid fixation member having a convex outer surface.

12. The intervertebral prosthetic device according toclaim 11, wherein the convex lowermost surface is configured to rest within a corresponding concave indentation formed in a second vertebral body adjacent thereto.

13. An intervertebral prosthetic device for implantation in a spine comprising:

a fixation member configured to be placed in a cavity of a vertebral body, the fixation member comprising:

an outer member configured to be placed against bone of the vertebral body;

an inner member opposite the outer member; and

at least one adjustment element that extends between the outer and inner members and that is configured to adjust a length dimension of the fixation member along its longitudinal axis;

a compressible member configured to be placed in a cavity in an intervertebral disc adjacent the vertebral body and configured to be secured to the inner member of the fixation member; and

a spacer sized to fit between the outer and inner members of the fixation member to maintain the fixation member at a desired length dimension.

14. The intervertebral prosthetic device according toclaim 13, wherein the outer and inner members of the fixation member comprise outer and inner plates, respectively.

15. The intervertebral prosthetic device according toclaim 14, wherein the inner plate of the fixation member includes a notch through which a portion of the spacer extends.

16. The intervertebral prosthetic device according toclaim 15, wherein the portion comprises a peg.

17. The intervertebral prosthetic device according toclaim 13, wherein the spacer includes a peg.

18. The intervertebral prosthetic device according toclaim 17, wherein the compressible member includes a well dimensioned to receive the peg in a snap fit.

19. The intervertebral prosthetic device according toclaim 13, wherein the compressible member has a bottom plate with a convex lowermost surface.

20. The intervertebral prosthetic device according toclaim 19, wherein the convex lowermost surface is configured to rest within a corresponding concave indentation formed in a second vertebral body adjacent thereto.

21. An intervertebral prosthetic device for implantation in a spine, comprising:

a fixation member configured to be placed in a cavity of a vertebral body, the fixation member comprising:

an outer member configured to be placed against bone of the vertebral body;

an inner member opposite the outer member; and

a longitudinal axis extending between the outer and inner members; and

a compressible member configured to be placed in a cavity in an intervertebral disc and to be secured to the inner member of the fixation member,

wherein:

(A) the compressible member is constructed to remain compressible after implantation, and

(B) the outer member includes a tab extending outward along an axis different from the longitudinal axis.

22. The intervertebral prosthetic device according toclaim 21, wherein the outer and inner members of the fixation member comprise outer and inner plates, respectively.

23. The intervertebral prosthetic device according toclaim 21, wherein the compressible member has a bottom plate with a convex lowermost surface.

24. The intervertebral prosthetic device according toclaim 23, wherein the convex lowermost surface is configured to rest within a corresponding concave indentation formed in a second vertebral body adjacent thereto.

25. An intervertebral prosthetic device for implantation in a spine, comprising:

a fixation member configured to be placed in a cavity of a vertebral body, the fixation member comprising:

an outer member configured to be placed against bone of the vertebral body;

an inner member opposite the outer member; and

a longitudinal axis extending between the outer and inner members;

a compressible member configured to be placed in a cavity in an intervertebral disc adjacent the vertebral body and configured to be secured to the fixation member; and

at least one anchor element configured to immobilize and/or stabilize the compressible member and/or the fixation member.

26. The intervertebral prosthetic device according toclaim 25, wherein compressible member is constructed to remain compressible after implantation and has at least one compressible element that remains compressible after implantation.

27. The intervertebral prosthetic device according toclaim 25, wherein the anchor element is dimensioned to extend into at least one of the fixation member and the compressible member and through bone adjacent to at least one of the fixation member and the compressible member.

28. An intervertebral prosthetic device according toclaim 25, wherein the anchor element extends through bone adjacent the outer member of the fixation member and into the outer member.

29. The intervertebral prosthetic device according toclaim 25, wherein the compressible member has a bottom plate with a convex lowermost surface.

30. The intervertebral prosthetic device according toclaim 29, wherein the convex lowermost surface is configured to rest within a corresponding concave indentation formed in a second vertebral body adjacent thereto.

31. A prosthetic device comprising:

a fixation member sized to fit within a cavity in a first vertebral body; and

a compressible member comprising:

a cup-shaped base member;

an upper member; and

one or more compressible elements provided between the base member and the upper member,

wherein the compressible member is sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body.

32. The prosthetic device according toclaim 31, wherein the base member of the compressible member is configured to engage the fixation member and the upper member of the compressible member is configured to engage a second vertebral body.

33. The prosthetic device according toclaim 31, wherein the cup-shaped base member has a wall, and wherein one or more slots are provided in the wall.

34. A prosthetic device comprising:

a fixation member sized to fit within a cavity in a first vertebral body; and

a compressible member comprising:

a base member;

an upper member that includes a spike; and

one or more compressible elements provided between the base member and the upper member,

wherein the one or more compressible elements are sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body.

35. The prosthetic device according toclaim 34, wherein the base member of the compressible member is configured to engage the fixation member and the upper member of the compressible member is configured to engage a second vertebral body.

36. A prosthetic device comprising:

a fixation member sized to fit within a cavity in a first vertebral body; and

a compressible member comprising:

a base member;

an upper member comprising a ball-and-socket joint; and

one or more compressible elements provided between the base member and the upper member,

wherein the compressible member is sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body.

37. The prosthetic device according toclaim 36, wherein the upper member further comprises a plate supporting the ball-and-socket joint, and wherein the ball-and-socket joint comprises a spike.

38. The prosthetic device according toclaim 36, wherein:

(i) the base member of the compressible member is configured to engage the fixation member, and

(ii) the upper member of the compressible member is configured to engage a second vertebral body.

39. The prosthetic device according toclaim 36, wherein the ball-and-socket joint is configured to be fixed or to remain mobile upon implantation.

40. A prosthetic device comprising:

a fixation member sized to fit within a cavity in a first vertebral body; and

a compressible member comprising:

a base member;

an upper member; and

one or more compressible elements provided between the base member and the upper member,

wherein:

(A) the compressible member is sized to substantially replace a nucleus pulposus of an intervertebral disc adjacent the vertebral body, and

(B) the base member is adjustable in a radial direction.

41. The prosthetic device according toclaim 40, wherein the base member is adjustable by means of a rotatable plate having a plurality of projections.

42. The prosthetic device according toclaim 41, wherein when the rotatable plate rotates, the projections engage and radially extend a plurality of extendable leaves.

43. A method of spinal prosthetic implantation, the method comprising the step of:

creating a cavity in a first vertebral body;

cutting a first hole through either a lower or an upper endplate of the vertebral body and through the nucleus pulposus of a first intervertebral disc adjacent thereto, thereby creating a first opening in the first intervertebral disc;

cutting a second hole through the other of the lower and upper endplate of the vertebral body and through the nucleus pulposus of a second intervertebral disc adjacent thereto, thereby creating a second opening in the second intervertebral disc;

implanting a first compressible member into one of the first and second openings;

implanting a second compressible member into the other of the first or second openings; and

implanting a fixation member into the cavity in the first vertebral body.

44. The method according toclaim 43, further comprising the step of adjusting a length of the fixation member.

45. The method according toclaim 43, further comprising the step of creating a first seat in an endplate of a second vertebral body below the first vertebral body.

46. The method according toclaim 45, further comprising the step of creating a second seat in an endplate of a third vertebral body above the first vertebral body, wherein each of the first and second seats is configured to receive a respective one of the first and second compressible members.

47. The method according toclaim 43, further comprising the step of positioning, in the fixation member, at least one of bone allograft, bone cement, and a bioresorbable polymer.

48. The method according toclaim 43, wherein the step of implanting a first compressible member into one of the first and second opening comprises providing a plurality of compressible elements in the first compressible member, wherein the plurality of compressible elements vary in a degree to which they are compressible.

49. The method according toclaim 43, wherein:

(i) the first compressible member comprises a base member that is wider than the hole cut in the vertebral body through which the first compressible member is implanted, and

(ii) the step of implanting the first compressible member into one of the first and second openings comprises the steps of: (a) maneuvering the base member of the first compressible member so that it passes through the hole in the one of the first and second openings; and (b) rotating the base member so that it substantially covers the hole.

50. The method according toclaim 43, wherein:

(i) the first compressible member comprises a base member that is radially adjustable to be wider than the hole cut in the vertebral body through which the first compressible member is implanted, and

(ii) the step of implanting the first compressible member into one of the first and second openings comprises the steps of: (a) maneuvering the base member of the first compressible member so that it passes through the hole in the one of the first and second openings; and (b) radially expanding the base member so that it substantially covers the hole.

51. A method of spinal prosthetic implantation, the method comprising the steps of:

creating a cavity in a first vertebral body;

cutting through an endplate of the vertebral body and through the nucleus pulposus of an adjacent intervertebral disc, thereby creating an opening in the intervertebral disc;

cutting into the cortical bone of a second vertebral body on the other side of the intervertebral disc to create a seat;

implanting a compressible member into the opening in the intervertebral disc such that a distal end of the compressible member sits within the seat in the second vertebral body; and

implanting a fixation member in the cavity in the first vertebral body.

52. The method according toclaim 51, further comprising the step of adjusting a length of the fixation member.

53. A method of spinal prosthetic implantation, the method comprising the step of:

creating a cavity in a vertebral body;

cutting a hole through either a lower or an upper endplate of the vertebral body and through the nucleus pulposus of an intervertebral disc adjacent thereto, thereby creating an opening in the intervertebral disc;

implanting a compressible member into the opening in the intervertebral disc; and

implanting a fixation member into the cavity in the first vertebral body,

wherein:

(i) the compressible member comprises a base member that is wider than the hole cut in the vertebral body through which the first compressible member is implanted, and

(ii) the step of implanting the compressible member into the opening comprises the steps of: (a) maneuvering the base member of the compressible member so that it passes through the hole and into the opening; and (b) rotating the base member so that it substantially covers the hole.

54. The method according toclaim 53, further comprising the step of creating a seat in an endplate of a second vertebral body on the other side of the intervertebral disc in which the opening is formed.

55. A method of spinal prosthetic implantation, the method comprising the step of:

creating a cavity in a vertebral body;

cutting a hole through either a lower or an upper endplate of the vertebral body and through the nucleus pulposus of an intervertebral disc adjacent thereto, thereby creating an opening in the intervertebral disc;

implanting a compressible member into the opening in the intervertebral disc; and

implanting a fixation member into the cavity in the first vertebral body,

wherein:

(i) the compressible member comprises a base member that is radially adjustable to be wider than the hole cut in the vertebral body through which the compressible member is implanted, and

(ii) the step of implanting the compressible member into the opening comprises the steps of: (a) maneuvering the base member of the compressible member so that it passes through the hole and into the opening; and (b) radially adjusting the base member so that it substantially covers the hole.

56. The method according toclaim 55, further comprising the step of creating a seat in an endplate of a second vertebral body on the other side of the intervertebral disc in which the opening is formed.

57. A drill guide for use in spinal surgery, comprising a body having a first leg and a second leg, wherein:

(A) the first leg is dimensioned to be fixed relative to an intervertebral prosthetic member mounted in a cavity of a first vertebral body,

(B) the second leg is dimensioned to extend from the first leg, adjacent the first vertebral body, to a free end, adjacent at least one of an intervertebral disc and a second vertebral body, and

(C) the second leg includes at least one drilling channel extending through the second leg and the free end of the second leg comprises a drill positioning block through which the at least one drilling channel extends.

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