POSTERIOR PROSTHETIC INTERVERTEBRAL DISC

Abstract

A prosthetic intervertebral disc is formed of first and second end plates sized and shaped to fit within an intervertebral space and to be implanted from the back of the patient, thereby decreasing the invasiveness of the procedure. The posterior approach provides for a smaller posterior surgical incision and avoids important blood vessels located anterior to the spine particularly for lumbar disc replacements. The first and second plates are each formed of first, second and third parts are arranged in a first configuration in which the parts are axially aligned to form a low profile device appropriate for insertion through the small opening available in the TLIF or PLIF approaches described above. The three parts of both of the plates rotate and translate with respect to one another in situ to a second configuration or a deployed configuration in which the parts are axially unaligned with each other to provide a maximum coverage of the vertebral end plates for a minimum of insertion profile. Upon deployment of the disc, a height of the disc is increased.

Claims

1. A method of deploying an implant in a spine of a patient, the method comprising: providing an implant having first and second interconnected elongated articulating portions with vertebral contacting outer surfaces, each of the first and second elongated articulating portions having a length, a width, a height and an axis extending along the length, wherein the length is longer than the width and the height; arranging the first and second elongated articulating portions with their axes substantially aligned in an insertion configuration; inserting the implant having the first and second interconnected elongated articulating portions and the vertebral contacting outer surfaces into a disc space between two vertebrae in the insertion configuration in which the implant has a first width; deploying the implant having the first and second interconnected elongated articulating portions inside the disc space by pivoting the first and second interconnected elongated articulating portions from the aligned insertion configuration to an unaligned deployed configuration in which the axes of the first and second elongated articulating portions are axially unaligned with each other and the implant has a second width greater than the first width, wherein the implant in the deployed configuration has vertebral contacting outer surfaces in contact with the two vertebrae; and increasing a height of the implant having the first and second interconnected elongated articulating portions by expanding the entire implant from an initial height to a deployed height while the implant is inside the disc space, wherein the initial height and deployed height are measured at a same location of the implant between the vertebral contacting outer surfaces.

2. The method of claim 1, wherein the first and second elongated articulating portions each comprise a pivot at one end thereof for deploying the implant.

3. The method of claim 2, wherein the second elongated articulating portion comprises a coupling for connecting to a deployment instrument at an end opposite the first elongated articulating portion.

4. The method of claim 1, wherein the step of inserting is performed by a PLIF approach in the spine.

5. The method of claim 1, wherein the step of inserting is performed by a TLIF approach in the spine.

6. The method of claim 1, wherein outer vertebral contacting surfaces of the first and second elongated articulating portions comprise teeth, grooves or ridges.

7. The method of claim 6, wherein the teeth, grooves or ridges are angled to ease insertion and prevent migration.

8. The method of claim 1, wherein the implant is inserted by a deployment instrument fixed to an end of the disc in the axially aligned insertion configuration.

9. The method of claim 3, further comprising attaching the deployment instrument to the coupling and inserting the implant with the deployment instrument.

10. The method of claim 1, wherein the step of deploying the implant from the aligned insertion configuration to the unaligned deployed configuration is caused by contact of a leading end of the implant with an annulus of the natural disc.

11. The method of claim 1, wherein the step of deploying the implant includes pivoting of the first and second elongated articulating portions of the implant with respect to one another.

12. The method of claim 1, wherein the step of increasing the height of the implant is performed during the deploying step.

13. The method of claim 1, wherein the step of increasing the height of the implant is performed after the deploying step.

14. The method of claim 1, wherein the inserting step and the deploying step are performed through a single posterior opening into the disc space.

15. The method of claim 1, wherein the deployed height is at least 1.5 times the height in the insertion configuration.

16. A method of deploying an implant in a spine of a patient, the method comprising: providing an implant having first and second interconnected elongated articulating portions with vertebral contacting outer surfaces, each of the first and second elongated articulating portions having a length, a width, a height and an axis extending along the length, wherein the length is longer than the width and the height; arranging the first and second elongated articulating portions with their axes substantially aligned in an insertion configuration; inserting the implant having the first and second interconnected elongated articulating portions and the vertebral contacting outer surfaces into a disc space between two vertebrae in the insertion configuration in which the implant has a first width; deploying the implant having the first and second interconnected elongated articulating portions inside the disc space by pivoting the first and second interconnected elongated articulating portions from the aligned insertion configuration to an unaligned deployed configuration in which the axes of the first and second elongated articulating portions are axially unaligned with each other and the implant has a second width greater than the first width, wherein the implant in the deployed configuration has vertebral contacting outer surfaces in contact with the two vertebrae; and increasing a height of the implant having the first and second interconnected elongated articulating portions by expanding the implant from an initial height to a deployed height while the implant is inside the disc space, wherein the initial height and deployed height are measured at a same location of the implant between the vertebral contacting outer surfaces, wherein said increasing a height comprises rotating and sliding of at least one of said first and second interconnected elongated articulating portions about at least one pivot, said at least one pivot extending primarily in a direction perpendicular to said vertebral contacting outer surfaces.

17. The method of claim 16, wherein the second elongated articulating portion comprises a coupling for connecting to a deployment instrument at an end opposite the pivot.

18. The method of claim 16, wherein the step of inserting is performed by a PLIF approach in the spine.

19. The method of claim 16, wherein the step of inserting is performed by a TLIF approach in the spine.

20. The method of claim 16, wherein outer vertebral contacting surfaces of the first and second elongated articulating portions comprise teeth, grooves or ridges.

21. The method of claim 16, wherein the implant is inserted by a deployment instrument fixed to an end of the disc in the axially aligned insertion configuration.

22. The method of claim 17, further comprising attaching the deployment instrument to the coupling and inserting the implant with the deployment instrument.

23. The method of claim 16, wherein the step of deploying the implant from the aligned insertion configuration to the unaligned deployed configuration is caused by contact of a leading end of the implant with an annulus of the natural disc.

24. The method of claim 16, wherein the step of deploying the implant includes pivoting of the first and second elongated articulating portions of the implant with respect to one another.

25. The method of claim 16, wherein the step of increasing the height of the implant is performed during the deploying step.

26. The method of claim 16, wherein the step of increasing the height of the implant is performed after the deploying step.

27. The method of claim 16, wherein the inserting step and the deploying step are performed through a single posterior opening into the disc space.

28. The method of claim 16, wherein the deployed height is at least 1.5 times the height in the insertion configuration.

29. A method of deploying an implant in a spine of a patient, the method comprising: providing an implant comprising: a first articulating portion with vertebral contacting outer surfaces, the first articulating portion having a length, a width, a height and an axis extending along the length, wherein the length is longer than the width and the height; and a second articulating portion pivotally interconnected to the first articulating portion, the second articulating portion having an axis; arranging the first and second interconnected articulating portions with their axes substantially aligned in an insertion configuration; inserting the implant having the first and second interconnected articulating portions into a disc space between two vertebrae in the insertion configuration; deploying the implant having the first and second interconnected articulating portions inside the disc space by pivoting the first and second interconnected articulating portions from the aligned insertion configuration to an unaligned deployed configuration in which the axes of the first and second articulating portions are axially unaligned with each other, wherein the implant in the deployed configuration has vertebral contacting outer surfaces in contact with the two vertebrae; and increasing a height of the implant having the first and second interconnected articulating portions by expanding the implant from an initial height to a deployed height while the implant is inside the disc space, wherein the initial height and deployed height are measured at a same location of the implant between the vertebral contacting outer surfaces, wherein said increasing comprises sliding a portion of at least one of said first and second interconnected articulating portions along at least one ramp formed in said implant, said sliding causing said increasing a height.

30. The method of claim 29, wherein the first and second articulating portions each comprise a pivot at one end thereof for deploying the implant.

31. The method of claim 29, wherein the second articulating portion comprises a coupling for connecting to a deployment instrument at an end opposite the pivot.

32. The method of claim 29, wherein the step of inserting is performed by a PLIF approach in the spine.

33. The method of claim 29, wherein the step of inserting is performed by a TLIF approach in the spine.

34. The method of claim 29, wherein outer vertebral contacting surfaces comprise teeth, grooves or ridges.

35. The method of claim 29, wherein the implant is inserted by a deployment instrument fixed to an end of the disc in the axially aligned insertion configuration.

36. The method of claim 31, further comprising attaching the deployment instrument to the coupling and inserting the implant with the deployment instrument.

37. The method of claim 29, wherein the step of deploying the implant from the aligned insertion configuration to the unaligned deployed configuration is caused by contact of a leading end of the implant with an annulus of the natural disc.

38. The method of claim 29, wherein the step of deploying the implant includes pivoting of the first and second articulating portions of the implant with respect to one another.

39. The method of claim 29, wherein the step of increasing the height of the implant is performed after the deploying step.

40. The method of claim 29, wherein the sliding portion slides on the ramp in the direction of the axis.

41. The method of claim 29, wherein the deployed height is at least 1.5 times the height in the insertion configuration.

42. A method of deploying an implant in a spine of a patient, the method comprising: providing an implant having first and second interconnected elongated articulating portions with vertebral contacting outer surfaces, each of the first and second elongated articulating portions having a length, a width, a height and an axis extending along the length, wherein the length is longer than the width and the height and wherein the first and second elongated articulating portions are interconnected and pivotable; arranging the first and second elongated articulating portions with their axes substantially aligned in an insertion configuration; connecting an end of the second elongated articulating portion to a deployment instrument; inserting the implant having the first and second interconnected elongated articulating portions and vertebral contacting outer surfaces into a disc space between two vertebrae in the insertion configuration; and contacting a leading end of the first elongated articulating portion with an annulus of the natural disc to cause the implant to articulate inside the disc space from the aligned insertion configuration to an unaligned deployed configuration in which the axes of the first and second elongated articulating portions are axially unaligned with each other; expanding the implant having the first and second interconnected elongated articulating portions in a height direction between the vertebral contacting outer surfaces while the implant is inside the disc space, wherein said increasing a height comprises rotating and sliding of at least one of said first and second interconnected elongated articulating portions about at least one pivot, said at least one pivot extending primarily in a direction perpendicular to said vertebral contacting outer surfaces; and disconnecting the deployment instrument from the second elongated articulating portion.

43. The method of claim 42, wherein the step of increasing a height of the implant comprises increasing a maximum height of the implant from an initial maximum height between the vertebral contacting outer surfaces to a deployed maximum height between the vertebral contacting outer surfaces.

44. The method of claim 42, wherein the leading end of the disc implant which contacts the annulus of the natural disc to cause the implant to articulate inside the disc space is has a curved portion.

45. The method of claim 42, wherein the step of expanding the implant in the height direction comprises increasing the height of both the first and second articulating portions of the implant.

46. A method of deploying an implant in a spine of a patient, the method comprising: providing an implant comprising: a first articulating portion with vertebral contacting outer surfaces, the first articulating portion having a length, a width, a height and an axis extending along the length, wherein the length is longer than the width and the height; and a second articulating portion pivotally interconnected to the first articulating portion, the second articulating portion having an axis: first and second elongated articulating portions are interconnected and pivotable; arranging the first and second interconnected articulating portions with their axes substantially aligned in an insertion configuration; connecting an end of the second articulating portion to a deployment instrument; inserting the implant having the first and second elongated articulating portions into a disc space between two vertebrae in the insertion configuration; and contacting a leading end of the first articulating portion with an annulus of the natural disc to cause the implant to articulate inside the disc space from the aligned insertion configuration to an unaligned deployed configuration in which the axes of the first and second elongated articulating portions are axially unaligned with each other; expanding the implant having the first and second interconnected articulating portions in a height direction between the vertebral contacting outer surfaces while the implant is inside the disc space, wherein said expanding comprises sliding a portion of at least one of said first and second interconnected articulating portions along at least one ramp formed in said implant, said sliding causing said expanding; and disconnecting the deployment instrument from the second articulating portion.

47. The method of claim 46, wherein the step of inserting is performed by a PLIF approach.

48. The method of claim 46, wherein the leading end of the first elongated articulating portion which contacts the annulus of the natural disc to cause the implant to articulate inside the disc space is curved.

49. The method of claim 46, wherein the step of increasing a height of the implant comprises increasing a maximum height of the implant from an initial maximum height between the vertebral contacting outer surfaces to a deployed maximum height between the vertebral contacting outer surfaces.

50. The method of claim 46, wherein the step of increasing the height of the implant includes expanding substantially the entire implant from an initial height to a deployed height.

51. An implant comprising: first and second interconnected elongated articulating portions with vertebral contacting outer surfaces, each of the first and second elongated articulating portions having a length, a width, a height and an axis extending along the length, wherein the length is longer than the width and the height; wherein the first and second interconnected elongated articulating portions have a first configuration for insertion into a disc space and a second configuration upon deployment in the disc space, wherein in the first configuration the axes of the first and second interconnected elongated articulating portions are substantially axially aligned with each other and in a second configuration the axes of the portions are axially unaligned with each other, and wherein the first and second interconnected elongated articulating portions are configured to be deployed in situ from the first configuration to the second configuration by both pivoting; wherein the implant is expandable in the height direction between the vertebral contacting outer surfaces while the implant is inside the disc space by sliding a portion of at least one of said first and second elongated articulating portions along at least one ramp formed in said implant, said sliding causing said expanding.

52. The implant of claim 51, wherein the disc in the first configuration has a height and a width of less than 12 mm.

53. The implant of claim 51, wherein the implant is expandable in the height direction by expanding substantially the entire implant from an initial height to a deployed height.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a perspective view of a posterior prosthetic intervertebral disc in a narrow insertion configuration;

[0017] FIG. 2 is a side view of the disc of FIG. 1;

[0018] FIG. 3 is a top view of the disc of FIG. 1;

[0019] FIG. 4 is a side cross sectional view of the disc of FIG. 1 taken along the line 4-4 of FIG. 3;

[0020] FIG. 5 is a cross sectional view of the disc of FIG. 1 taken along the line 5-5 of FIG. 2;

[0021] FIG. 6 is a perspective view of the disc of FIG. 1 is an expanded deployed configuration;

[0022] FIG. 7 is a top view of the deployed disc of FIG. 6;

[0023] FIG. 8 is a top view of an alternative embodiment of a posterior prosthetic intervertebral disc in a partially deployed configuration;

[0024] FIG. 9 is a perspective view of the disc of FIG. 8;

[0025] FIG. 10 is a side view of the disc of FIG. 8;

[0026] FIG. 11 is a perspective view of the disc of FIG. 8 with the core moving along a track from the position of FIG. 8 to the fully deployed position of FIG. 12; and

[0027] FIG. 12 is a perspective view of the disc of FIG. 8 with the core in a fully deployed position.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention provides an implanted intervertebral disc assembly which both restores motion and can be implanted from the back of the patient, thereby decreasing the invasiveness of the procedure. The posterior approach provides for a smaller posterior surgical incision and avoids important blood vessels located anterior to the spine particularly for lumbar disc replacements. The intervertebral discs described herein are designed to be suitable for either a PLIF or TLIF approach to the spine. These approaches require insertion of a device with a small insertion profile which can be expanded or assembled in vivo into a complete disc assembly.

[0029] PLIF stands for Posterior Lumbar Interbody Fusion. In the PLIF approach to the spine, the vertebrae are reached through an incision in the patient's back (posterior). The PLIF procedure involves forming a 3-6 inch incision in the patient's back and retracting the spinal muscles to allow access to the vertebral disc. The surgeon then carefully removes the lamina (laminectomy) to be able to see and access the nerve roots. The facet joints, which lie directly over the nerve roots, may be trimmed to allow more room for the nerve roots. Depending on the amount of space available, to of the facets may be removed. The surgeon then removes some or all of the affected disc and surrounding tissue. Once the disc space is prepared, hardware, such as an intervertebral disc, is inserted into the disc space. The space available for insertion of the intervertebral disc can vary depending on the patient, but generally the opening has a width and height of about 1 cm which with distraction can form a slightly larger opening.

[0030] TLIF stands for Transforaminal Lumbar Interbody Fusion. The TLIF has recently gained popularity as a surgical access to the lumbar spine and provides some potential advantages over the PLIF approach. The TLIF technique involves approaching the spine in a similar manner as the PLIF approach but more from the side of the spinal canal through a midline incision in the patient's back. This approach greatly reduces the amount of surgical muscle dissection and minimizes the nerve manipulation required to access the vertebrae, discs and nerves. The TLIF approach is generally less traumatic to the spine, is safer for the nerves, and allows for minimal access. However, the TLIF involves the removal of at least one and possibly both facets.

[0031] FIG. 1 illustrates a prosthetic intervertebral disc 10 formed of first and second end plates 12, 14 sized and shaped to fit within an intervertebral space. Each plate 12, 14 has a vertebral contacting outer surface 16 and an inner surface carrying first and second bearing surfaces 18, 20 (shown in FIGS. 4 and 5). The first bearing surface 18 in the embodiment of FIG. 1 is a concave bearing surface while the second bearing surface 20 is a mating convex bearing surface. Together the bearing surfaces 18, 20 form a ball and socket joint arranged to allow articulation and rotation between the first and second plates 12, 14.

[0032] The first and second plates 12, 14 are each formed of first, second and third parts 22, 24, 26. The three parts 22, 24, 26 have a first configuration, shown in FIG. 1 in which the parts are axially aligned to form a low profile device appropriate for insertion through the small opening available in the TLIF or PLIF approaches described above. Preferably, the undeployed configuration of FIG. 1 has a height less than about 10 mm and a width less than about 12 mm. The three parts 22, 24, 26 of both of the plates 12, 14 rotate and translate with respect to one another in situ to a second configuration or a deployed configuration in which the parts are axially unaligned with each other. In the deployed configuration, as shown in FIGS. 6 and 7, the three parts form a substantially H-shaped configuration which provides a maximum coverage of the vertebral end plates for a minimum of insertion profile. As the three parts 22, 24, 26 translate with respect to one another to the deployed configuration a height of the disc is increased in a manner which will be described in detail below.

[0033] The bone integration surfaces 16 of the disc 10 have been shown as flat surfaces for ease of illustration. The outer vertebral body contacting surface 16 may take on any of the configurations known in the art. Oftentimes, the outer surfaces 16 will include one or more surface features and/or materials to enhance attachment of the disc 10 to vertebral bone. For example, the outer surfaces 16 may be machined to have serrations, teeth or other surface features for promoting adhesion of the plates 12, 14 to a vertebra. In one embodiment, serrations are provided on the outer surfaces 16. The serrations can be pyramid shaped serrations extending in mutually orthogonal directions, but other geometries of serrations or other features including teeth, grooves, ridges, pins, barbs and combinations thereof would also be useful. When the bone integration structures are ridges, teeth, barbs or similar structures, they may be angled to ease insertion and prevent migration. The outer surfaces may include other fixation means inserted after deployment of the disc 10, including one or more fins, pins, or screws. In one embodiment, one or more fins are provided on the last of the three parts to enter the disc space. Optionally, additional fins may be provided that are inserted after the disc is positioned by sliding the fin(s) into one or more slots in the endplates.

[0034] The outer surfaces 16 may be provided with a rough microfinish formed by blasting with aluminum oxide microparticles or the like to improve bone integration. In some embodiments, the outer surface 16 may also be titanium plasma sprayed or HA coated to further enhance attachment of the outer surface to vertebral bone.

[0035] The disc 10 may be deployed with the aid of various instruments including one or more distracters, sizing guides, placement instruments and deployment instruments. The deployment instruments can be fixed to the ends of the disc 10 in the insertion configuration shown in FIG. 1 by a connection means, such as a quick connect or a threaded coupling. The placement and deployment instruments generally include at least two instruments with one instrument inserted through each of the two openings formed at the posterior side of the disc space on either side of the spine. Referring now to FIG. 3, the sequence of deployment of the disc 10 includes rotation of the first and third parts 22, 26 with respect to the second part 24 in the direction of the arrows A, followed by sliding of the second part 24 along first and third parts in the direction of the arrow B to form the deployed configuration shown in FIGS. 6 and 7.

[0036] The disc 10 includes cylindrical pegs 30 on opposite ends of the second parts 24 which fit into channels 32 on the first and third parts 22, 26 to allow first rotation and then translation of the second part along the first and third parts. The rotation of the disc 10 from the substantially linear arrangement of FIGS. 1-3 to a substantially U-shaped arrangement (not shown) can be caused by contact of a leading end of the inserted disc with an annulus of the natural disc. The U-shaped configuration is then converted to the final H-shaped configuration by pulling the second part 24 posteriorly in the direction of the arrow B. The sliding of the second or center part 24 along the channels 32 causes the disc space to be distracted, i.e. the height of the disc increases from an initial height H.sub.i, shown in FIG. 2 to a deployed height H.sub.d, shown in FIG. 6. This distraction or separation of the end plates is provided by ramps 34 which lie along each side of the channel 32 in the first and third parts 22, 26. The deployed height H.sub.d is preferably between 1.3 and 2 times the initial height H.sub.i. In one example, the deployed height H.sub.d is about 1.5 times the initial height H.sub.i and provides a final deployed disc configuration shown in FIG. 6 which is significantly higher than the height of the access opening provided by the posterior PLIF or TLIF approach.

[0037] Another embodiment of a posterior prosthetic intervertebral disc 100 is shown in FIGS. 8-12. The prosthetic disc 100 includes first and second end plates 112, 114 sized and shaped to fit within an intervertebral space, each end plate having a vertebral contacting surface 116 and an opposite inner surface including a bearing surface 118. The disc 100 includes a mobile core 120 which in a deployed configuration is positioned between the opposing bearing surfaces 118 to provide a mobile core articulating disc design. As in the embodiment of FIG. 1, each of the plates 12, 114 are formed of first, second and third parts 122, 124, 126. The three parts of the plates have a first configuration for insertion of the disc 100 through a small posterior keyhole into the disc space. In the first configuration (not shown) the three parts 122, 124, 126 are substantially axially aligned. The after insertion, the three parts 122, 124, 126 are rotated by pivoting on interconnecting posts 130 to a second configuration in which the parts are axially unaligned with each other and arranged with the first and third parts 122, 126 at an angle of about 20-90 degrees with respect to one another, preferably about 70-85 degrees.

[0038] The mobile core 120 includes opposite convex bearing surfaces arranged to be received between the first and second bearing surfaces 118 of the plates to allow articulation, rotation and some translation between the first and second plates. As shown in FIGS. 8-10, for insertion of the disc 100 into the disc space, the core 120 is positioned in a seat 132 formed between the first parts 122 at one end of the first parts. After insertion of the disc 100 into the disc space, the core 120 is advanced along a track 134, shown in FIG. 11 from the seat 132 to a final deployed position between the bearing surfaces 118 of the plates. FIG. 12 shows the core 120 seated between the bearing surfaces 118. The bearing surfaces 118 may include one or more core retaining features, such as a retaining ring or other peripheral retaining features. As can be seen in FIG. 11, the movement of the mobile core 130 from the first position in the seat 132 to the second position between the bearing surfaces 118 distracts the plates 112, 114 away from one another and increases a height of the disc 100 from an initial height H.sub.i, shown in FIG. 10 to a deployed height H.sub.d shown in FIG. 12.

[0039] The procedure for replacing a natural intervertebral disc with the artificial intervertebral discs 10, 100 includes using a PLIF or TLIF approach to the spine, by forming a 3-6 inch incision in the patient's back and retracting the spinal muscles to allow access to the vertebral disc. The surgeon then carefully removes the lamina (laminectomy) to be able to see and access the nerve roots. The disc space is then entered through a preexisting opening or through an opening formed by cutting away a portion of or an entire one or more facet. Those skilled in the art will understand the procedure of preparing the disc space and implanting the disc which is summarized herein. A far posterio-lateral minimally invasive approach can be used so as to allow for the minimum of facet removal such that the facet joints remain substantially intact. The surgeon then removes some or all of the affected disc and surrounding tissue. Once the disc space is prepared the intervertebral disc is inserted into the disc space in the insertion configuration in which the first, second and third parts are aligned. The space available for insertion of the intervertebral disc can vary depending on the patient, but generally the opening has a width and height of about 1 cm which with distraction can form a slightly larger opening, i.e. about 1 cm by 1.2 cm. The deployment of the discs 10, 100 can be performed through a single posterior opening, or preferably, through two posterior openings to allow the surgeon better access to deploy the disc. In one embodiment, one of the two openings is used for insertion of the disc while the other opening is used for a distraction instrument and/or other deployment instruments.

[0040] The upper and lower plates 12, 14, 112, 114 may be constructed from any suitable metal, alloy or combination of metals or alloys, such as but not limited to cobalt chrome alloys, titanium (such as grade 5 titanium), titanium based alloys, tantalum, nickel titanium alloys, stainless steel, and/or the like. They may also be formed of ceramics, biologically compatible polymers including PEEK, UHMWPE, PLA or fiber reinforced polymers. The plates 12, 14, 112, 114 may be formed of a one piece construction or may be formed of more than one piece, such as different materials coupled together.

[0041] The core 130 can be made of low friction materials, such as titanium, titanium nitrides, other titanium based alloys, tantalum, nickel titanium alloys, stainless steel, cobalt chrome alloys, ceramics, or biologically compatible polymer materials including PEEK, UHMWPE, PLA or fiber reinforced polymers. High friction coating materials can also be used.

[0042] Different materials may be used for different parts of the disc 10 to optimize imaging characteristics. PEEK plates may also be coated with titanium plasma spray or provided with titanium screens for improved bone integration. Other materials and coatings can also be used such as titanium coated with titanium nitride, aluminum oxide blasting, HA (hydroxylapatite) coating, micro HA coating, and/or bone integration promoting coatings. Any other suitable metals or combinations of metals may be used as well as ceramic or polymer materials, and combinations thereof. Any suitable technique may be used to couple materials together, such as snap fitting, slip fitting, lamination, interference fitting, use of adhesives, welding and the like.

[0043] Although the present invention has been described as having a ball in socket design (disc 10) or a mobile core design (disc 100), the articulation surfaces may be varied to take on any of the different articulation designs known in the art. For example, the disc 10 may use a mobile bearing design in place of the ball and socket articulation. In one alternative embodiment of the invention non-symmetrically shaped bearing surfaces are used to tailor the articulation of the disc to the anatomy. In one example, the bearing surfaces are arranged to allow a maximum of 12 degrees of motion in flexion, a maximum of 8 degrees in extension and a maximum of 8 degrees in each direction of lateral bending. This configuration is useful particularly in the lumbar spine where the average range of motion of the various segments is larger in flexion that in extension or lateral bending.

[0044] Although the core 130 of FIG. 8 has been shown as circular in cross section with spherically shaped bearing surfaces, other shapes may be used including oval, elliptical, or kidney bean shaped. The circular shaped core does not limit rotational motion between the plates. The non-circular shaped cores can be used to limit rotational motion between the upper and lower plates 112, 113. When the core 130 is formed of a polymer such as PEEK which is invisible under radiographic imaging, it may be desirable to have a radiographic marker imbedded within the core.

[0045] While the exemplary embodiments have been described in some detail, by way of example and for clarity of understanding, those of skill in the art will recognize that a variety of modifications, adaptations, and changes may be employed. Hence, the scope of the present invention should be limited solely by the appended claims.