US20070050028A1 - Spinal implants and methods of providing dynamic stability to the spine - Google Patents

Abstract

The present application discloses a plurality of spinal implants and methods for repairing annular defects in intervertebral discs and for providing dynamic stability to the motion segment of the spine in the vicinity of the repaired disc. Each of the implants comprises a head portion and a tail portion. In the illustrated embodiments, the head portion of each implant is enlarged relative to the tail portion. Each of the head portions and tail portions is adapted to support adjacent vertebrae and resist collapse of the intervertebral disc. A tapered portion of each implant engages end plates of the adjacent vertebrae to resist forces tending to push the implant out of the intervertebral space. The tail portion of each implant includes a tail flange (which in some embodiments is of similar diameter to the head portion) that abuts extradiscal lips of the adjacent vertebrae and resists forces tending to push the implant deeper into the intervertebral space.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application claims priority to provisional application Ser. No. 60/711,714, filed on Aug. 26, 2005, the entire contents of which are hereby expressly incorporated by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to devices and methods for repairing annular defects in intervertebral discs and for providing dynamic stability to the motion segment of the spine in the vicinity of the repaired disc.
• 2. Description of the Related Art
• The vertebral spine is the axis of the skeleton upon which all of the body parts “hang.” In humans, the normal spine has seven cervical, twelve thoracic and five lumbar segments. The lumbar segments sit upon a sacrum, which then attaches to a pelvis, in turn supported by hip and leg bones. The bony vertebral bodies of the spine are separated by intervertebral discs, which act as joints, but allow known degrees of flexion, extension, lateral bending and axial rotation.
• Each intervertebral disc primarily serves as a mechanical cushion between the vertebral bones, permitting controlled motions within vertebral segments of the axial skeleton.FIG. 4 illustrates a healthyintervertebral disc30 andadjacent vertebrae32. Aspinal nerve34 extends along the spine posteriorly thereof.
• The normal disc is a unique, mixed structure, comprised of three component tissues: The nucleus pulposus (“nucleus”), the annulus fibrosus (“annulus”), and two opposing vertebral end plates. The two vertebral end plates are each composed of thin cartilage overlying a thin layer of hard, cortical bone which attaches to the spongy, richly vascular, cancellous bone of the vertebral body. The end plates thus serve to attach adjacent vertebrae to the disc. In other words, a transitional zone is created by the end plates between the malleable disc and the bony vertebrae.
• The annulus of the disc is a tough, outer fibrous ring that binds together adjacent vertebrae. This fibrous portion is generally about 10 to 15 millimeters in height and about 15 to 20 millimeters in thickness, although in diseased discs these dimensions may be diminished. The fibers of the annulus consist of 15 to 20 overlapping multiple plies, and are inserted into the superior and inferior vertebral bodies at roughly a 30 degree angle in both directions. This configuration particularly resists torsion, as about half of the angulated fibers will tighten when the vertebrae rotate in either direction, relative to each other. The laminated plies are less firmly attached to each other.
• Immersed within the annulus is the nucleus. The annulus and opposing end plates maintain a relative position of the nucleus in what can be defined as a nucleus cavity. The healthy nucleus is largely a gel-like substance having high water content, and similar to air in a tire, serves to keep the annulus tight yet flexible. The nucleus-gel moves slightly within the annulus when force is exerted on the adjacent vertebrae with bending, lifting, etc.
• Under certain circumstances, an annulus defect (or anulotomy) can arise that requires surgical attention. These annulus defects can be naturally occurring, surgically created, or both. A naturally occurring annulus defect is typically the result of trauma or a disease process, and may lead to a disc herniation.FIG. 5 illustrates aherniated disc36. A disc herniation occurs when the annulus fibers are weakened or torn and the inner tissue of the nucleus becomes permanently bulged, distended, or extruded out of its normal, internal annular confines. The mass of a herniated or “slipped”nucleus38 can compress aspinal nerve40, resulting in leg pain, loss of muscle control, or even paralysis.
• Where the naturally occurring annulus defect is relatively minor and/or little or no nucleus tissue has escaped from the nucleus cavity, satisfactory healing of the annulus may be achieved by immobilizing the patient for an extended period of time. However, many patients require surgery (microdiscectomy) to remove the herniated portion of the disc.FIG. 6 illustrates a disc from which a portion has been removed through a microdiscectomy procedure. After the traditional microdiscectomy, loss of disc space height may also occur because degenerated disc nucleus is removed as part of the surgical procedure. Loss of disc space height can also be a source of continued or new lumbar spine generated pain.
• Further, a more problematic annulus defect concern arises in the realm of anulotomies encountered as part of a surgical procedure performed on the disc space. Alternatively, with discal degeneration, the nucleus loses its water binding ability and deflates, as though the air had been let out of a tire. Subsequently, the height of the nucleus decreases, causing the annulus to buckle in areas where the laminated plies are loosely bonded. As these overlapping laminated plies of the annulus begin to buckle and separate, either circumferential or radial annular tears may occur, which may contribute to persistent and disabling back pain. Adjacent, ancillary spinal facet joints will also be forced into an overriding position, which may create additional back pain.
• In many cases, to alleviate pain from degenerated or herniated discs, the nucleus is removed and the two adjacent vertebrae surgically fused together. While this treatment may alleviate the pain, all discal motion is lost in the fused segment. Ultimately, this procedure places greater stress on the discs adjacent the fused segment as they compensate for the lack of motion, perhaps leading to premature degeneration of those adjacent discs. A more desirable solution entails replacing, in part or as a whole, the damaged nucleus with a suitable prosthesis having the ability to complement the normal height and motion of the disc while stimulating the natural disc physiology.
• Regardless of whether the annulus defect occurs naturally or as part of a surgical procedure, an effective device and method for repairing such defects, while at the same time providing for dynamic stability of the motion segment, would be of great benefit to sufferers of herniated discs and annulus defects.
SUMMARY OF THE INVENTION
• The preferred embodiments of the present spinal implants and methods of providing dynamic stability to the spine have several features, no single one of which is solely responsible for their desirable attributes. Without limiting the scope of these spinal implants and methods as expressed by the claims that follow, their more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of the Preferred Embodiments,” one will understand how the features of the preferred embodiments provide advantages, which include, inter alia, the capability to repair annular defects and stabilize adjacent motion segments of the spine without substantially diminishing the range of motion of the spine, simplicity of structure and implantation, and a low likelihood that the implant will migrate from the implantation site.
• One embodiment of the present spinal implants and methods of providing dynamic stability to the spine comprises a spinal implant adapted to be implanted in an intervertebral disc located between a first vertebral disc and a second vertebral disc to repair an annular defect in the intervertebral disc, and to provide dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc. The implant comprises a head portion including at least a first head segment and a second head segment. Each of the first and second head segments has a length greater than zero as measured along a longitudinal axis of the implant. The first head segment has a constant height along its length. The second head segment tapers along at least a portion of its length from a greater height to a lesser height away from the first head segment. The implant further comprises a tail portion extending from the head portion and including at least a first tail segment and a second tail segment. The first tail segment adjoins the second head segment. Each of the first and second tail segments has a length greater than zero as measured along a longitudinal axis of the implant. The first tail segment has a constant height along its length. The second tail segment tapers along at least a portion of its length from a lesser height to a greater height away from the first tail segment.
• Another embodiment of the present spinal implants and methods comprises a spinal implant adapted to be implanted in an intervertebral disc located between a first vertebral disc and a second vertebral disc to repair an annular defect in the intervertebral disc, and to provide dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc. The implant comprises a head portion including at least a first head segment and a second head segment. Each of the first and second head segments has a length greater than zero as measured along a longitudinal axis of the implant. The first head segment tapers along at least a portion of its length from a greater height to a lesser height away from the second head segment. The second head segment tapers along at least a portion of its length from a greater height to a lesser height away from the first head segment. The implant further comprises a tail portion extending from the head portion and including at least a first tail segment and a second tail segment. The first tail segment adjoins the second head segment. Each of the first and second tail segments has a length greater than zero as measured along a longitudinal axis of the implant. The first tail segment has a constant height along its length. The second tail segment tapers along at least a portion of its length from a lesser height to a greater height away from the first tail segment.
• Another embodiment of the present spinal implants and methods comprises a method of repairing an annular defect in an intervertebral disc located between a first vertebral disc and a second vertebral disc, and providing dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc. The method comprises the steps of removing at least a portion of the intervertebral disc, preparing an implantation site in the vicinity of the intervertebral disc, and implanting a spinal implant device at the implantation site. The step of preparing the implantation site includes the steps of reaming the implantation site to remove bone material from endplates of each of the first and second vertebral discs and thereby shape a portion of each of the endplates to receive the implant device in a substantially complementary fit, and countersinking the implantation site to remove bone material from extradiscal lips of each of the first and second vertebral discs and thereby shape a portion of each of the extradiscal lips to receive the implant device in a substantially complementary fit.
• Another embodiment of the present spinal implants and methods comprises a method of repairing an annular defect in an intervertebral disc located between a first vertebral disc and a second vertebral disc, and providing dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc. The method comprises the steps of removing at least a portion of the intervertebral disc, preparing an implantation site in the vicinity of the intervertebral disc, and implanting a spinal implant device at the implantation site. The implant comprises a head portion including at least a first head segment and a second head segment. Each of the first and second head segments has a length greater than zero as measured along a longitudinal axis of the implant. The first head segment has a constant height along its length. The second head segment tapers along at least a portion of its length from a greater height to a lesser height away from the first head segment. A tail portion extends from the head portion and includes at least a first tail segment and a second tail segment. The first tail segment adjoins the second head segment. Each of the first and second tail segments has a length greater than zero as measured along a longitudinal axis of the implant. The first tail segment has a constant height along its length. The second tail segment tapers along at least a portion of its length from a lesser height to a greater height away from the first tail segment.
• Another embodiment of the present spinal implants and methods comprises a tool for removing bone material from facing endplates of adjacent vertebrae. The tool comprises a head portion that extends from a distal end of a shaft. The head portion includes at least an outwardly tapering segment and an inwardly tapering segment. At least a fraction of the head portion includes a roughened surface and/or blades adapted to remove bone material.
• Another embodiment of the present spinal implants and methods comprises a tool for removing bone material from extradiscal lips of adjacent vertebrae. The tool comprises a head portion and a tail portion extending from a distal end of a shaft. The head portion includes at least an outwardly tapering segment and an inwardly tapering segment. At least a fraction of the tail portion includes a roughened surface adapted to remove bone material.
• Another embodiment of the present spinal implants and methods comprises a tool for removing bone material from extradiscal lips of adjacent vertebrae. The tool comprises a head portion extending from a distal end of a shaft. The head portion includes at least an outwardly tapering segment and an inwardly tapering segment. At least a fraction of the distal end of the shaft includes blades adapted to remove bone material.
• Another embodiment of the present spinal implants and methods comprises a tool for measuring a distance between adjacent vertebrae. The tool comprises a substantially cylindrical shaft.
• Another embodiment of the present spinal implants and methods comprises a trial implant for measuring an implant space between adjacent vertebrae. The tool comprises a head portion extending from a distal end of a shaft. The head portion includes at least an outwardly tapering segment and an inwardly tapering segment.
BRIEF DESCRIPTION OF THE DRAWINGS
• The preferred embodiments of the present spinal implants and methods of providing dynamic stability to the spine, illustrating their features, will now be discussed in detail. These embodiments depict the novel and non-obvious spinal implants and methods shown in the accompanying drawings, which are for illustrative purposes only. These drawings include the following figures, in which like numerals indicate like parts:
• FIG. 1 is a front perspective view of one embodiment of the present spinal implants;
• FIG. 2 is a front elevational view of the spinal implant ofFIG. 1;
• FIG. 3 is a right-side elevational view of the spinal implant ofFIG. 1;
• FIG. 4 is a right-side elevational view of a normal intervertebral disc, the adjacent vertebrae and a spinal nerve;
• FIG. 5 is a right-side elevational view of a herniated intervertebral disc, the adjacent vertebrae and a spinal nerve;
• FIG. 6 is a right-side elevational view of the disc ofFIG. 5 after a microdiscectomy procedure;
• FIG. 7 is a right-side elevational view of the disc ofFIG. 6 and the implant ofFIG. 1;
• FIG. 8 is a right-side elevational view of the disc and the implant ofFIG. 7, showing the implant implanted within the disc;
• FIG. 9 is a right-side elevational view of the disc ofFIG. 6 and one embodiment of a reaming tool that may be used during a procedure to implant the implant ofFIG. 1;
• FIG. 10 is a right-side elevational view of the disc ofFIG. 9 after the reaming step, and a countersinking tool that may be used during a procedure to implant the implant ofFIG. 1;
• FIG. 11 is a right-side elevational view of the disc ofFIG. 10 after the countersinking step, and a sizing tool that may be used during a procedure to implant the implant ofFIG. 1;
• FIG. 12 is a right-side elevational view of the disc ofFIG. 11 after the sizing step, and a trial implant that may be used during a procedure to implant the implant ofFIG. 1;
• FIG. 13 is a right-side elevational view of the disc ofFIG. 12 and the implant ofFIG. 1, showing the implant implanted within the disc;
• FIG. 14 is a front perspective view of another embodiment of the present spinal implants;
• FIG. 15 is a front elevational view of the spinal implant ofFIG. 14;
• FIG. 16 is a right-side elevational view of the spinal implant ofFIG. 14;
• FIG. 17 is a front perspective view of another embodiment of the present spinal implants;
• FIG. 18 is a front elevational view of the spinal implant ofFIG. 17;
• FIG. 19 is a right-side elevational view of the spinal implant ofFIG. 17;
• FIG. 20 is a front perspective view of another embodiment of the present spinal implants;
• FIG. 21 is a front elevational view of the spinal implant ofFIG. 20;
• FIG. 22 is a right-side elevational view of the spinal implant ofFIG. 20;
• FIG. 23 is a front perspective view of another embodiment of a reaming tool that may be used during a procedure to implant the present implants;
• FIG. 24 is a right-side elevational view of the reaming tool ofFIG. 23;
• FIG. 25 is a front perspective view of another embodiment of a countersinking tool that may be used during a procedure to implant the present implants;
• FIG. 26 is a right-side elevational view of the countersinking tool ofFIG. 25;
• FIG. 27 is a front perspective view of another embodiment of a sizing tool that may be used during a procedure to implant the present implants;
• FIG. 28 is a right-side elevational view of the sizing tool ofFIG. 27;
• FIG. 29 is a front perspective view of another embodiment of a trial implant that may be used during a procedure to implant the present implants; and
• FIG. 30 is a right-side elevational view of the trial implant ofFIG. 29.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIGS. 1-3 illustrate one embodiment of the present spinal implants. Theimplant42 is shaped as a contoured plug having anenlarged head portion44 and a relatively narrow tail portion46 (FIG. 3). In the illustrated embodiment, cross-sections taken perpendicularly to a longitudinal axis of theimplant42 are all substantially circular. However, the area of a given cross-section varies along the longitudinal axis.
• With reference toFIG. 3, thehead portion44 includes a substantiallyflat nose48 at a first end of aconical segment50. The conical segment increases in height and cross-sectional area at a substantially constant rate from the nose to a first end of a largecylindrical segment52. The large cylindrical segment extends at a constant height and cross-sectional area from the conical segment to a first end of atapered segment54. The tapered segment decreases in height and cross-sectional area at an increasing rate from the large cylindrical segment to a first end of a smallcylindrical segment56. The small cylindrical segment is substantially smaller in diameter than the large cylindrical segment, and extends at a constant height and cross-sectional area from the tapered segment to atail flange58. The tail flange flares outwardly from a minimum height and cross-sectional area at a second end of the small cylindrical segment to a maximum height and cross-sectional area at a second end of theimplant42. The maximum height of the tail flange is approximately equal to that of the large cylindrical segment.
• Those of ordinary skill in the art will appreciate that the illustrated shape of theimplant42, including the relative dimensions of thesegments50,52,54,56 and theflange58, is merely one example. For example, cross-sections of theimplant42 taken along the longitudinal axis may be oval or elliptical or rectangular instead of circular. Also, the ratio of the diameter of the smallcylindrical segment56 to the diameter of the largecylindrical segment52 may be lesser or greater, for example. Also, theimplant42 need not include the substantiallycylindrical segments52,56. For example, theimplant42 may continue to taper from thenose48 all the way to the taperedsegment54, and the smallcylindrical segment56 may be reshaped to resemble adjoining tapered segments joined by a neck of a minimum diameter. Furthermore, the anatomy of annular defects and of vertebral end plates has wide variations. Accordingly, theimplant42 may be manufactured in a variety of shapes and sizes to fit different patients. A plurality of differently sized implants may, for example, be available as a kit to surgeons so that during an implantation procedure a surgeon can select the proper size implant from a range of size choices.FIGS. 14-22, described in more detail below, illustrate implants having sample alternative shapes and sizes.
• Theimplant42 is preferably constructed of a durable, biocompatible material. For example, bone, polymers or metals may be used. Examples of suitable polymers include silicone, polyethylene, polypropylene, polyetheretherketone, polyetheretherketone resins, etc. In some embodiments, the material is non-compressible, so that theimplant42 can provide dynamic stability to the motion segment, as explained in detail below. In certain other embodiments, the material may be compressible.
• FIG. 6 illustrates anintervertebral disc60 that has undergone a microdiscectomy procedure. A portion of the disc nucleus has been removed leaving a void62. As shown inFIGS. 7 and 8, theimplant42 is adapted to be inserted between the neighboringvertebrae64 to fill the void62. Once implanted, the contoured body of theimplant42, including theenlarged head portion44 and the relativelynarrow tail portion46, may provide support to theadjacent vertebrae64, resisting any tendency of these vertebrae to move closer to one another. However, in many cases thevertebrae64 are not naturally shaped to provide mating engagement with theimplant42. AsFIG. 8 shows, theimplant42 may sometimes be too large to fit within the intervertebral space, causing the neighboringvertebrae64 to be forced apart.
• To avoid the ill fitting engagement shown inFIG. 8,FIGS. 9-13 illustrate one embodiment of a method for implanting theimplant42 ofFIGS. 1-3. In these figures, a portion of theintervertebral disc60 has been removed through a microdiscectomy procedure. Before any disc material is removed, the implanting physician may visualize the implantation site using, for example, magnetic resonance imaging, or any other visualization technique. The visualization step allows the physician to determine what size and shape of implant is best suited to the procedure, which in turn allows the physician to determine what size and shape of tools to use during the procedure.
• Before theimplant42 is introduced, theintervertebral space62 and theadjacent vertebrae64 may be prepared so that theimplant42 will fit properly. For example, each of theadjacent vertebrae64 includes anend plate66. In a healthy spine, these end plates abut the intervertebral discs. In the spine ofFIGS. 9-13, these end plates will abut theimplant42 after it is implanted. Accordingly, the end plates may be shaped so that they have a mating or complementary fit with respect to the contouredimplant42 and enable theimplant42 to maintain its desired position within the intervertebral space.
• FIG. 9 illustrates one embodiment of a reamingtool68 that is adapted to shape theend plates66 ofadjacent vertebrae64. The reamingtool68 includes ahead portion70 that extends from a distal end of ashaft72. Thehead portion70 and theshaft72 may be formed integrally with one another, or thehead portion70 may be secured to theshaft72 by any known means. The head portion and shaft are preferably rigid, and may be made of a metal, for example. In the illustrated embodiment, the head portion is shaped substantially the same as theimplant42, and includes aconical segment74, a largecylindrical segment76, atapered segment78, a smallcylindrical segment80 and atail flange82. Those of ordinary skill in the art will appreciate that the illustrated size and shape of thehead portion70 is merely an example. However, it is advantageous for the head portion to be of similar size and shape to the implant that will ultimately be implanted in the intervertebral space62 (whether that size and shape is the same as or different from theimplant42 ofFIGS. 1-3).
• At least a leading portion of theconical segment74 includes a smooth outer surface. This smooth surface facilitates the entry of thehead portion70 into theintervertebral space62, as described below. The smallcylindrical segment80 andtail flange82 also each include a smooth outer surface. A trailing portion of theconical segment74, the largecylindrical segment76 and the taperedsegment78 each include a roughened surface. This surface may, for example, be knurled or burred. The roughened surface is adapted to remove bone from thevertebral end plates66 in order to reshape the end plates so that they have a mating or complementary fit with respect to the contouredimplant42. Those of ordinary skill in the art will appreciate that fewer or more segments of thehead portion70 may be roughened in order to provide desired capabilities for shaping theend plates66.
• To insert thehead portion70 into theintervertebral space62, the surgeon positions thenose84 of the head portion adjacent theextradiscal lips86 on theadjacent vertebrae64, as shown inFIG. 9. Then, applying digital pressure along the longitudinal axis of theshaft72, the surgeon may push thehead portion70 into the void62 between the adjacent vertebrae. Alternatively, the surgeon may strike a proximal end of theshaft72 with a mallet to drive thehead portion70 into the void62. Thehead portion70 forces theadjacent vertebrae64 apart as it penetrates. Often, the adjacent vertebrae are resistant to being forced apart and significant force must be applied along the axis of theshaft72 to force thehead portion70 into the void62. The smooth surface at the leading end of theconical portion74, which reduces friction between the head portion and theextradiscal lips86, facilitates the entry of the head portion into the comparativelysmall void62.
• To remove material from theend plates66, the surgeon rotates theshaft72. He or she may apply a rotational force to the shaft using his or her fingers or a gripping instrument. Alternatively, a proximal end of the shaft may engage a powered drill, which may impart a rotational force to the shaft. The rotatingshaft72 rotates the head portion so that the roughened surfaces on theconical portion74, the largecylindrical segment76 and the taperedsegment78 scrape material from theend plates66. The surgeon continues to remove bone material until the end plates achieve a desired surface contour to complement or mate with theimplant42, as shown inFIG. 10. The surgeon then removes thehead portion70 from the void62 by applying digital pressure along theshaft72, or by employing an instrument such as a slap hammer.
• FIG. 10 illustrates one embodiment of acountersinking tool88 that is adapted to shape theextradiscal lips86 of the adjacent vertebrae. A surgeon may use the countersinking tool in order to shape the extradiscal lips so that they more closely complement or mate with thetail flange58 and prevent theimplant42 from being pushed into theintervertebral space62.
• The countersinkingtool88 includes ahead portion90 that extends from a distal end of ashaft92. Thehead portion90 and theshaft92 may be formed integrally with one another, or thehead portion90 may be secured to theshaft92 by any known means. The head portion and shaft are preferably rigid, and may be made of a metal, for example. In the illustrated embodiment, the head portion is shaped substantially the same as theimplant42, and includes aconical segment94, a largecylindrical segment96, atapered segment98, a smallcylindrical segment100 and atail flange102. Those of ordinary skill in the art will appreciate that the illustrated size and shape of thehead portion90 is merely an example.
• Theconical segment94, largecylindrical segment96, taperedsegment98, and smallcylindrical segment100 each include a smooth outer surface. The smooth surfaces facilitate the entry of thehead portion90 into theintervertebral space62, as described above with respect to the reamingtool68. Thetail flange102 includes a roughened surface. This surface may, for example, be knurled or burred. The roughened surface is adapted to remove bone from theextradiscal lips86 in order to reshape the lips so that they provide a surface that complements or mates with the contouredimplant42.
• The surgeon inserts thehead portion90 into theintervertebral space62 in the same manner as described above with respect to thehead portion70. Thehead portion90 preferably fits within the void62 such that the roughened surface on thetail flange102 abuts theextradiscal lips86. To remove material from thelips86, the surgeon rotates theshaft92. As with the reamingtool68, the surgeon may impart a rotational force to theshaft92 using his or her fingers, a gripping instrument or a powered drill, for example. The rotatingshaft72 rotates the head portion so that the roughened surface on thetail flange102 scrapes material from thelips86. The surgeon continues to remove bone material until the end plates achieve a surface contour to complements or mates with theimplant42, as shown inFIG. 11. The surgeon then removes thehead portion90 from the void62 in the same manner as described above with respect to thehead portion70.
• After the surgeon has shaped the vertebral end plates and extradiscal lips, he or she may use a sizing tool to measure the width of the opening between thevertebral end plates66.FIG. 11 illustrates one embodiment of asizing tool104. The tool comprises a cylindrical shaft of a known diameter. The surgeon may have several sizing tools of varying diameters close at hand during an implantation procedure. By attempting to insert sizing tools of increasing or decreasing diameters into the opening between thevertebral end plates66, the surgeon can measure the size of the opening. After measuring the distance between thevertebral end plates66, the surgeon will select the appropriate size of implant. He or she may begin with a trial implant, such as theimplant106 shown inFIG. 12.
• In the illustrated embodiment, thetrial implant106 is shaped exactly as theimplant42 ofFIGS. 1-3, and is secured to the distal end of ashaft108. The trial implant may be permanently or temporarily secured to the shaft. The surgeon may insert thetrial implant106 into the void62 in the same manner as described above with respect to thehead portions70,90. The smooth surface of thetrial implant106 facilitates its entry into the void62. Theconical portion108 forces thevertebrae64 apart as the surgeon advances thetrial implant108. Then, as the extradiscal lips pass over the largecylindrical segment110 and reach thetapered segment112, the vertebrae snap shut around the implant and the extradiscal lips come to rest around the smallcylindrical segment114. If the surgeon determines that the trial implant is the proper size to fit within the void, then he or she will withdraw the trial implant in the same manner as described above with respect to thehead portions70,90. He or she will then select an implant that is the same size and shape as thetrial implant108, and insert the selected implant into the void62, as shown inFIG. 13. Theimplant42 may be temporarily secured to the distal end of a shaft (not shown), such that the insertion procedure is substantially the same as that described above with respect to thetrial implant108. If the implant is temporarily secured to the distal end of a shaft, it may engage the shaft through a threaded connection, for example. Once the implant is in place, the surgeon can then remove the shaft by unscrewing it from the implant.
• Theimplant42 advantageously stabilizes the region of the spine where it is implanted without substantially limiting the mobility of the region. As shown inFIG. 13, theconical segment50, the largecylindrical segment52, the taperedsegment54 and the smallcylindrical segment56 each abut and support thevertebral end plates66, preventing thevertebrae64 from moving closer to one another. Further, interengagement of theshaped end plates66 and the taperedsegment54 resists any forces tending to push theimplant42 out of the intervertebral space, while interengagement of thetail flange58 and the shapedextradiscal lips86 resists any forces tending to push theimplant42 deeper into the intervertebral space. The border of the defect in the disc annulus (not visible inFIG. 13) comes to rest on the smallcylindrical segment56 and thetail flange58, thus preventing any disc nucleus from being squeezed out of the defect.
• Those of skill in the art will appreciate that the implantation procedure described above could be performed using a guard device that would not only prevent surrounding tissue from interfering with the procedure, but also protect the surrounding tissue from damage. For example, a tubular guard (not shown) may be employed around the implantation site. The guard would prevent surrounding tissue from covering the implantation site, and prevent the implantation instruments from contacting the surrounding tissue.
• In certain embodiments of the present methods, the spacing between adjacent vertebrae is preferably maintained. Thus, the spacing between adjacent vertebrae after one of the present implants has been inserted therebetween is preferably approximately the same as the spacing that existed between those same vertebrae prior to the implantation procedure. In such a method it is unnecessary for the implanting physician to distract the vertebrae prior to introducing the implant. As described above, the increasing size of the conical segment and the large cylindrical segment of the implant temporarily distracts the vertebrae as it passes between the discal lips thereof, after which the vertebrae snap shut around the implant. In certain other embodiments of the present methods, however, it may be advantageous to increase the spacing of the adjacent vertebrae through the implantation procedure, so that the spacing between the adjacent vertebrae after the implant has been inserted therebetween is greater than the spacing that existed between those same vertebrae prior to the implantation procedure. In such embodiments, the implanting physician may distract the adjacent vertebrae prior to implanting the implant in order to achieve the desired spacing.
• FIGS. 14-22 illustrate alternative embodiments of the present spinal implants. These alternative embodiments are adapted for use in spinal discs where the patient's anatomy is better suited to an implant having a different size and/or shape. For example,FIGS. 14-16 illustrate aspinal implant116 having anenlarged head portion118 and a relatively narrow tail portion120 (FIG. 16). As in theimplant42 ofFIGS. 1-3, thehead portion118 of theimplant116 ofFIGS. 14-16 includes a substantiallyflat nose122, aconical segment124, a largecylindrical segment126 and atapered segment128. Thetail portion120 includes a smallcylindrical segment130 and atail flange132. In comparing the embodiment ofFIGS. 1-3 to the embodiment ofFIGS. 14-16, theconical segment50 is longer than theconical segment124, and the largecylindrical segment52 is wider in diameter than the largecylindrical segment126. Thetail flange58 is also somewhat wider in diameter than thetail flange132. Thus, theimplant116 ofFIGS. 14-16 is adapted for implantation in an intervertebral disc having a relatively small diameter, or where it is advantageous for theimplant116 to penetrate only a relatively short distance into the disc.
• FIGS. 17-19 illustrate aspinal implant134 having anenlarged head portion136 and a relatively narrow tail portion138 (FIG. 19). Cross-sections taken perpendicularly to a longitudinal axis of the implant are all substantially circular, however, the area of a given cross-section varies along the longitudinal axis. As in the implants described above (and as with all implants described herein and encompassed by the claims below), the cross-sectional shape of theimplant134 need not be circular, and could be, for example, elliptical or oval. Further, the cross-sectional shapes of the implants described herein may vary along the longitudinal axis.
• Thehead portion136 includes a substantiallyflat nose140 at a first end of aconical segment142. The conical segment increases in height and cross-sectional area at a substantially constant rate from the nose to a first end of a largecylindrical segment144. The large cylindrical segment extends at a constant height and cross-sectional area from the conical segment to a first end of atapered segment146. The tapered segment decreases in height and cross-sectional area at an increasing rate from the large cylindrical segment to a first end of a smallcylindrical segment148. The small cylindrical segment is substantially smaller in height than the large cylindrical segment, and extends from the tapered segment to atail flange150. The tail flange flares outwardly from a minimum height and cross-sectional area at a second end of the small cylindrical segment to a maximum height and cross-sectional area at a second end of theimplant134. The maximum height of the tail flange is approximately equal to that of the large cylindrical segment.
• A comparison between theimplant116 ofFIGS. 14-16 and theimplant134 ofFIGS. 17-19 reveals that theimplant134 ofFIGS. 17-19 has a longer largecylindrical segment144 and a longer smallcylindrical segment148. The remaining segments in theimplant134 are substantially similar to their counterparts in theimplant116. Theimplant134 ofFIGS. 17-19 is thus adapted for implantation in an intervertebral disc where it is advantageous for theimplant134 to penetrate a greater distance into the disc as compared to theimplant116 ofFIGS. 14-16.
• FIGS. 20-22 illustrate aspinal implant152 having a shape that is similar to theimplant42 ofFIGS. 1-3. Theimplant152 includes anenlarged head portion154 and a relatively narrow tail portion156 (FIG. 22). As in theimplant42 ofFIGS. 1-3, thehead portion154 of theimplant152 ofFIGS. 20-22 includes a substantiallyflat nose158, aconical segment160 and atapered segment162. However, theimplant152 does not include a large cylindrical segment. Instead, the conical segment directly adjoins the tapered segment, and the tapered segment tapers at a more gradual rate as compared to the taperedsegment54 of theimplant42 ofFIGS. 1-3. Thehead portion154 achieves a maximum height at the junction between theconical segment160 and thetapered segment162. This area of maximum height is adapted to provide stability to the adjacent vertebrae. As with theimplant42 ofFIGS. 1-3, thetail portion156 of theimplant152 ofFIGS. 20-22 includes a smallcylindrical segment164 and atail flange166.
• Those of skill in the art will appreciate that the relative dimensions shown in the figures are not limiting. For example, inFIG. 13 theimplant42 is illustrated as having certain dimensions relative to the dimensions of thevertebrae64. In fact, the size of the implant relative to the vertebrae will be chosen based upon a variety of factors, including the patient's anatomy and the size of the annular defect to be repaired. In certain applications the implant may be significantly smaller relative to the vertebrae, and may extend significantly less than halfway toward a vertical centerline of the intervertebral disc. In certain other applications the implant may be significantly larger relative to the vertebrae, and may extend almost all the way across the intervertebral disc.
• FIGS. 23 and 24 illustrate analternative reaming tool168 that may be used to shape the end plates of adjacent vertebrae. Thereaming tool168, which is similar to the reamingtool68 described above and pictured inFIG. 9, includes ahead portion170 that extends from a distal end of ashaft172. Thehead portion170 and theshaft172 may be formed integrally with one another, or thehead portion170 may be secured to theshaft172 by any known means. Thehead portion170 andshaft172 are preferably rigid, and may be made of a metal, for example. In the illustrated embodiment, thehead portion170 is shaped similarly to theimplant42, and includes aconical segment174, a largecylindrical segment176, atapered segment178 and a small cylindrical segment180 (FIG. 24). Those of ordinary skill in the art will appreciate that the illustrated size and shape of thehead portion170 is merely an example. However, it is advantageous for thehead portion170 to be of similar size and shape to the implant that will ultimately be implanted in the intervertebral space (whether that size and shape is the same as or different from theimplant42 ofFIGS. 1-3). In the illustrated embodiment, theshaft172 has a greater width relative to thehead portion170 as compared to the reamingtool68 described above, thereby making thereaming tool168 easier to grip.
• A plurality of curved blades182 (FIG. 23) extend along the surfaces of theconical segment174, the largecylindrical segment176, thetapered segment178 and the smallcylindrical segment180, giving the head portion170 a scalloped surface. Theblades182 extend in a substantially helical pattern along a longitudinal axis of thehead portion170. Each pair ofadjacent blades182 is separated by acavity183. Theblades182 are adapted to remove bone from thevertebral end plates66 in order to reshape the end plates so that they provide a surface that is complementary to the contouredimplant42. Operation of thereaming tool168 is substantially identical to operation of the reamingtool68 described above. Theblades182 scrape bone material away as thereaming tool168 is rotated, and thecavities183 provide a volume to entrain removed bone material.
• FIGS. 25 and 26 illustrate analternative countersinking tool184 that may be used to shape the extradiscal lips of adjacent vertebrae. Thecountersinking tool184, which is similar to thecountersinking tool88 described above and pictured inFIG. 10, includes ahead portion186 that extends from a distal end of ashaft188. Thehead portion186 and theshaft188 may be formed integrally with one another, or thehead portion186 may be secured to theshaft188 by any known means. Thehead portion186 andshaft188 are preferably rigid, and may be made of a metal, for example. In the illustrated embodiment, thehead portion186 is shaped similarly to theimplant42. Those of ordinary skill in the art will appreciate that the illustrated size and shape of thehead portion186 is merely an example. However, it is advantageous for thehead portion186 to be of similar size and shape to the implant that will ultimately be implanted in the intervertebral space (whether that size and shape is the same as or different from theimplant42 ofFIGS. 1-3). In the illustrated embodiment, theshaft188 has a greater width relative to thehead portion186 as compared to thecountersinking tool88 described above, thereby making thecountersinking tool184 easier to grip.
• A plurality ofcurved blades190 extend around adistal end192 of theshaft188, adjacent thehead portion186. An edge of eachblade190 faces thehead portion186, and each pair ofadjacent blades190 is separated by a wedge-shapedcavity194. Theblades190 are adapted to remove bone from the extradiscal lips of adjacent vertebrae in order to reshape the vertebrae so that they provide a surface that is complementary to the contouredimplant42. Operation of thecountersinking tool184 is substantially identical to operation of thecountersinking tool88 described above. Theblades190 scrape bone material away as thecountersinking tool184 is rotated, and thecavities194 provide a volume to entrain removed bone material.
• FIGS. 27 and 28 illustrate another embodiment of asizing tool196. The tool comprises acylindrical shaft198 of a known diameter that extends from adistal end200 of ahandle portion202. Operation of thesizing tool196 is substantially identical to operation of thesizing tool104 described above. However, thesizing tool196 ofFIGS. 27 and 28 advantageously has ahandle portion202 that is wider than thecylindrical shaft198, thereby making thesizing tool196 easier to grip.
• FIGS. 29 and 30 illustrate another embodiment of atrial implant204. Thetrial implant204, which comprises animplant portion206 and ahandle portion208, is similar to thetrial implant106 described above. However, thetrial implant204 of FIGS.29 and30 advantageously has awider handle portion204, thereby making thetrial implant204 easier to grip.
SCOPE OF THE INVENTION
• The above presents a description of the best mode contemplated for carrying out the present spinal implants and methods of providing dynamic stability to the spine, and of the manner and process of making and using them, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains to make and use these spinal implants and methods. These spinal implants and methods are, however, susceptible to modifications and alternate constructions from that discussed above that are fully equivalent. Consequently, these spinal implants and methods are not limited to the particular embodiments disclosed. On the contrary, these spinal implants and methods cover all modifications and alternate constructions coming within the spirit and scope of these spinal implants and methods are as generally expressed by the following claims, which particularly point out and distinctly claim the subject matter of these spinal implants and methods.

Claims (15)

1. A spinal implant adapted to be implanted in an intervertebral disc located between a first vertebral disc and a second vertebral disc to repair an annular defect in the intervertebral disc, and to provide dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, comprising:

a head portion including at least a first head segment and a second head segment, each of the first and second head segments having a length greater than zero as measured along a longitudinal axis of the implant, the first head segment having a constant height along its length, the second head segment tapering along at least a portion of its length from a greater height to a lesser height away from the first head segment; and

a tail portion extending from the head portion and including at least a first tail segment and a second tail segment, the first tail segment adjoining the second head segment, each of the first and second tail segments having a length greater than zero as measured along a longitudinal axis of the implant, the second tail segment tapering along at least a portion of its length from a lesser height to a greater height away from the first tail segment.

2. The spinal implant ofclaim 1, wherein the first tail segment has a constant height along its length.

3. The spinal implant ofclaim 1, wherein upon permanent implantation within the intervertebral disc the head portion abuts and supports facing endplates of the first and second vertebral discs to aid in preventing collapse of the intervertebral disc while providing dynamic stability to the motion segment, and the tail portion abuts and supports the facing endplates to further aid in preventing collapse of the intervertebral disc while providing dynamic stability to the motion segment, and also abuts extradiscal lips of the first and second vertebral discs to thereby prevent the implant from penetrating the intervertebral disc beyond a desired amount.

4. The spinal implant ofclaim 1, wherein the head portion further includes at least a third head segment that extends from the first head segment opposite the second head segment.

5. The spinal implant ofclaim 4, wherein the third head segment tapers along at least a portion of its length from a greater height to a lesser height away from the first head segment.

6. The spinal implant ofclaim 1, wherein cross-sections of the implant taken along the longitudinal axis thereof are circular, oval, elliptical or rectilinear.

7. The spinal implant ofclaim 1, wherein the implant is constructed of one or more of bone, polymers or metals.

8. A spinal implant adapted to be implanted in an intervertebral disc located between a first vertebral disc and a second vertebral disc to repair an annular defect in the intervertebral disc, and to provide dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, comprising:

a head portion including at least a first head segment and a second head segment, each of the first and second head segments having a length greater than zero as measured along a longitudinal axis of the implant, the first head segment tapering along at least a portion of its length from a greater height to a lesser height away from the second head segment, the second head segment tapering along at least a portion of its length from a greater height to a lesser height away from the first head segment; and

a tail portion extending from the head portion and including at least a first tail segment and a second tail segment, the first tail segment adjoining the second head segment, each of the first and second tail segments having a length greater than zero as measured along a longitudinal axis of the implant, the first tail segment having a constant height along its length, the second tail segment tapering along at least a portion of its length from a lesser height to a greater height away from the first tail segment.

9. The spinal implant ofclaim 8, wherein the tapered portion of the first head segment tapers at a constant rate.

10. The spinal implant ofclaim 8, wherein the tapered portion of the second head segment tapers at a rate that increases away from the first head segment.

11. The spinal implant ofclaim 8, wherein the head portion further includes at least a third head segment having a length greater than zero that is interposed between the first head segment and the second head segment.

12. The spinal implant ofclaim 11, wherein the third head segment has a constant height along its length.

13. A method of repairing an annular defect in an intervertebral disc located between a first vertebral disc and a second vertebral disc, and providing dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, the method comprising the steps of:

removing at least a portion of the intervertebral disc;

preparing an implantation site in the vicinity of the intervertebral disc; and

implanting a spinal implant device at the implantation site;

wherein the step of preparing the implantation site includes the steps of:

reaming the implantation site to remove bone material from endplates of each of the first and second vertebral discs and thereby shape a portion of each of the endplates to receive the implant device in a substantially complementary fit; and

countersinking the implantation site to remove bone material from extradiscal lips of each of the first and second vertebral discs and thereby shape a portion of each of the extradiscal lips to receive the implant device in a substantially complementary fit.

14. The method ofclaim 13, further comprising the step of measuring a distance between the endplates to determine an appropriate size for the implant device.

15. A method of repairing an annular defect in an intervertebral disc located between a first vertebral disc and a second vertebral disc, and providing dynamic stability to a motion segment of a spine in the vicinity of the intervertebral disc, the method comprising the steps of:

removing at least a portion of the intervertebral disc;

preparing an implantation site in the vicinity of the intervertebral disc; and

implanting a spinal implant device at the implantation site;

wherein the implant comprises a head portion including at least a first head segment and a second head segment, each of the first and second head segments having a length greater than zero as measured along a longitudinal axis of the implant, the first head segment having a constant height along its length, the second head segment tapering along at least a portion of its length from a greater height to a lesser height away from the first head segment, and a tail portion extending from the head portion and including at least a first tail segment and a second tail segment, the first tail segment adjoining the second head segment, each of the first and second tail segments having a length greater than zero as measured along a longitudinal axis of the implant, the first tail segment having a constant height along its length, the second tail segment tapering along at least a portion of its length from a lesser height to a greater height away from the first tail segment.

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