Intervertebral prosthetic disc with metallic core

Abstract

A prosthetic disc for insertion between adjacent vertebrae includes a core having upper and lower curved surfaces and upper and lower plates. At least one of the curved surfaces of the core is metallic, and in some embodiments the entire core is metallic. Each plate has an outer surface which engages a vertebra and a metallic inner curved surface which is shaped to slide over one of the curved surfaces of the core. In some embodiments, the center of rotation of the core is free to move relative to the upper and lower metallic plates. In some embodiments, one or more channels extend across one or both of the curved surfaces of the core for allowing passage of bodily fluid to promote lubrication between the core and at least one of the plates.

Claims

1. A method for assembling a prosthetic disc for insertion between adjacent vertebrae, the method comprising: .Iadd.providing a core with at least one curved surface;.Iaddend. movably coupling .[.a.]. .Iadd.the .Iaddend.core with a first metallic endplate to form an interference fit between the core and the first metallic endplate, wherein each .Iadd.of the at least one .Iaddend.curved .[.surface.]. .Iadd.surfaces .Iaddend.of the core comprises a metal.Iadd., wherein coupling the core with the first metallic endplate comprises: heating the first endplate sufficiently to cause it to expand; contacting a portion of the core with the expanded endplate; and allowing the first endplate to cool, thus contracting to form the interference fit around the portion of the core.Iaddend.; and contacting the core with a second metallic endplate.

.[. 2. A method as in claim 1, wherein coupling the core with the first metallic endplate comprises: heating the first endplate sufficiently to cause it to expand; contacting a portion of the core with the expanded endplate; and allowing the first endplate to cool, thus contracting to form the interference fit around the portion of the core. .].

.[. 3. A method as in claim 1, wherein coupling the core with the first endplate comprises forming the endplate around the core. .].

.[. 4. A method as in claim 1, wherein coupling the core with the first endplate comprises engaging a peripheral protrusion of the core with a peripheral restraining structure of the first endplate. .].

5. A method .[.as in claim 1,.]. .Iadd.for assembling a prosthetic disc for insertion between adjacent vertebrae, the method comprising: providing a core with at least one curved surface; movably coupling the core with a first metallic endplate to form an interference fit between the core and the first metallic endplate, wherein each of the at least one curved surfaces of the core comprises a metal, .Iaddend.wherein coupling the core with the first endplate comprises screwing the core into the first endplate via complementary threads on the core and the first endplate.Iadd.; and contacting the core with a second metallic endplate.Iaddend..

6. A method for assembling a prosthetic disc for insertion between adjacent vertebrae, the method comprising: providing a first metallic endplate having a first bearing surface; movably coupling a core with the first metallic endplate to form an interference fit between the core and the first metallic endplate, wherein a bearing surface of the core corresponds to a shape of the first bearing surface.Iadd., wherein the core has circumferentially spaced recesses and at least one of the first or second plates has a plurality of pins or pegs opposing corresponding recesses of the core.Iaddend.; and contacting the core with a second metallic endplate.

7. A method .[.as in claim 6,.]. .Iadd.for assembling a prosthetic disc for insertion between adjacent vertebrae, the method comprising: providing a first metallic endplate having a first bearing surface; movably coupling a core with the first metallic endplate to form an interference fit between the core and the first metallic endplate, wherein a bearing surface of the core corresponds to a shape of the first bearing surface, .Iaddend.wherein coupling the core with the first metallic endplate comprises: heating the first endplate sufficiently to cause it to expand; contacting a portion of the core with the expanded endplate; and allowing the first endplate to cool, thus contracting to form the interference fit around the portion of the core.Iadd.; and contacting the core with a second metallic endplate.Iaddend..

8. A method as in claim 6, wherein coupling the core with the first endplate comprises forming the endplate around the core.

9. A method as in claim .[.6.]. .Iadd.15.Iaddend., wherein coupling the core with the first endplate comprises engaging a peripheral protrusion of the core with .[.a.]. .Iadd.the .Iaddend.projecting .[.restraining.]. structure .[.of the first endplate.]., wherein the projecting .[.restraining.]. structure engages and retains the peripheral protrusion.

10. A method .[.as in claim 6,.]. .Iadd.for assembling a prosthetic disc for insertion between adjacent vertebrae, the method comprising: providing a first metallic endplate having a first bearing surface; movably coupling a core with the first metallic endplate to form an interference fit between the core and the first metallic endplate, wherein a bearing surface of the core corresponds to a shape of the first bearing surface, .Iaddend.wherein coupling the core with the first endplate comprises screwing the core into the first endplate via complementary threads on the core and the first endplate.Iadd.; and contacting the core with a second metallic endplate.Iaddend..

.Iadd.11. A method for assembling a prosthetic disc for insertion between adjacent vertebrae, the method comprising: providing a first metallic endplate having a first bearing surface; movably coupling a core with the first metallic endplate to form an interference fit between the core and the first metallic endplate, wherein a bearing surface of the core corresponds to a shape of the first bearing surface, wherein coupling the core with the first metallic endplate comprises passing outwardly facing surfaces of a peripheral structure on the core through opposing inwardly facing surfaces of a projecting structure on at least one of the first or second metallic plates, and wherein a distance between the outwardly facing surfaces of the peripheral structure on the core is less than a distance between the opposing inwardly facing surfaces of the projecting structure so that the peripheral structure on the core will pass through the projecting structure to restrain peripheral movement of the core; and contacting the core with a second metallic endplate..Iaddend.

.Iadd.12. A method as in claim 11, wherein the interference fit retains the core against the first bearing surface of the first metallic plate but allows the core to slide freely within a limit defined by the projecting structure..Iaddend.

.Iadd.13. A method as in claim 11, wherein the projecting structure comprises a pin or peg projecting from at least one of the first or second metallic plates..Iaddend.

.Iadd.14. A method as in claim 11, wherein: the projecting structure projects from the first or second plate by a distance; the bearing surface of the core that corresponds to the shape of the first bearing surface of the first metallic plate is a first core bearing surface; the core further comprises a second core bearing surface configured to engage the second metallic plate; and a central region of the first core bearing surface is separated from a central region of the second core bearing surface by a core thickness greater than the distance that the projecting structure projects from the first or second metallic plate..Iaddend.

.Iadd.15. A method for assembling a prosthetic disc for insertion between adjacent vertebrae, the method comprising: providing a first metallic endplate having a first bearing surface; movably coupling a core with the first metallic endplate to form an interference fit between the core and the first metallic endplate, wherein a bearing surface of the core corresponds to a shape of the first bearing surface, wherein the interference fit retains the core against the first bearing surface of the first metallic plate but allows the core to slide freely within a limit defined by a projecting structure; and contacting the core with a second metallic endplate..Iaddend.

.Iadd.16. A method as in claim 15, wherein the projecting structure comprises a pin or peg projecting from at least one of the first or second metallic plates..Iaddend.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 1A are cross-sectional anterior views of a prosthetic disc with the prosthesis plates and core in vertical alignment, according to embodiments of the present invention;

(2) FIG. 2 is a side view of the prosthetic disc in FIG. 1 after sliding movement of the plates over the core;

(3) FIG. 3 is a side view of the prosthetic disc in FIG. 1 after translational movement of the plates relative to the core;

(4) FIG. 4 is a side view of the prosthetic disc in FIG. 1 with the prosthesis plates and core in vertical alignment;

(5) FIG. 5 is a perspective view of a core of a prosthetic disc, according to one embodiment of the present invention; and

(6) FIG. 6 is a superior view of an upper plate of a prosthetic disc, according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) Various embodiments of the present invention generally provide for an intervertebral disc prosthesis having upper and lower plates and a core having at least one metallic surface. In various embodiments, the core may have a mobile center of rotation, one or more surface channels for promoting passage of lubricating fluid, or both. FIGS. 1-6 generally demonstrate one embodiment of such a prosthesis. The general principles of the present invention, however, may be applied to any of a number of other disc prostheses, such as but not limited to the LINK SB CHARITE disc prosthesis (provided by DePuy Spine, Inc.) the MOBIDISK disc prosthesis (provided by LDR Medical), the BRYAN cervical disc prosthesis (provided by Medtronic Sofamor Danek, Inc.), the PRODISC disc prosthesis or PRODISC-C disc prosthesis (from Synthes Stratec, Inc.), and the PCM disc prosthesis (provided by Cervitech, Inc.).

(8) That being said, and with reference now to FIGS. 1-4 a prosthetic disc 10 for intervertebral insertion between two adjacent spinal vertebrae (not shown) suitably includes an upper plate 12, a lower plate 14 and a core 16 located between the plates. The upper plate 12 includes an outer surface 18 and an inner surface 24 and may be constructed from any suitable metal, alloy or combination of metals or alloys, such as but not limited to cobalt chrome molybdenum, titanium (such as grade 5 titanium), stainless steel and/or the like. In one embodiment, typically used in the lumbar spine, the upper plate 12 is constructed of cobalt chrome molybdenum, and the outer surface 18 is treated with aluminum oxide blasting followed by a titanium plasma spray. In another embodiment, typically used in the cervical spine, the upper plate 12 is constructed of titanium, the inner surface 24 is coated with titanium nitride, and the outer surface 18 is treated with aluminum oxide blasting. An alternative cervical spine embodiment includes no coating on the inner surface 24. In other cervical and lumbar disc embodiments, any other suitable metals or combinations of metals may be used. In some embodiments, it may be useful to couple two materials together to form the inner surface 24 and the outer surface 18. For example, the upper plate 12 may be made of an MRI-compatible material, such as titanium, but may include a harder material, such as cobalt chrome molybdenum, for the inner surface 24. Any suitable technique may be used to couple materials together, such as snap fitting, slip fitting, lamination, interference fitting, use of adhesives, welding and/or the like. Any other suitable combination of materials and coatings may be employed in various embodiments of the invention.

(9) In some embodiments, the outer surface 18 is planar. Oftentimes, the outer surface 18 will include one or more surface features and/or materials to enhance attachment of the prosthesis 10 to vertebral bone. For example, the outer surface 18 may be machined to have serrations 20 or other surface features for promoting adhesion of the upper plate 12 to a vertebra. In the embodiment shown (seen best in FIG. 6), the serrations 20 extend in mutually orthogonal directions, but other geometries would also be useful. Additionally, the outer surface 18 may be provided with a rough microfinish formed by blasting with aluminum oxide microparticles or the like. In some embodiments, the outer surface may also be titanium plasma sprayed to further enhance attachment of the outer surface 18 to vertebral bone.

(10) The outer surface 18 may also carry an upstanding, vertical fin 22 extending in an anterior-posterior direction. The fin 22 is pierced by transverse holes 23. In alternative embodiments, the fin 22 may be rotated away from the anterior-posterior axis, such as in a lateral-lateral orientation, a posterolateral-anterolateral orientation, or the like. In some embodiments, the fin 22 may extend from the surface 18 at an angle other than 90. Furthermore, multiple fins 22 may be attached to the surface 18 and/or the fin 22 may have any other suitable configuration, in various embodiments. In other embodiments, the fin 22 In some embodiments, such as discs 10 for cervical insertion, the fins 22, 42 may be omitted altogether.

(11) The inner, spherically curved concave surface 24 is formed at a central (from right to left), axial position with a circular recess 26 as illustrated. At the outer edge of the curved surface 24, the upper plate 12 carries peripheral restraining structure comprising an integral ring structure 26 including an inwardly directed rib or flange 28. The flange 28 forms part of a U-shaped member 30 joined to the major part of the plate by an annular web 32. The flange 28 has an inwardly tapering shape and defines upper and lower surfaces 34 and 36 respectively which are inclined slightly relative to the horizontal when the upper plate 12 is at the orientation seen in FIG. 1. An overhang 38 of the U-shaped member 30 has a vertical dimension that tapers inwardly as illustrated.

(12) The lower plate 14 is similar to the upper plate 12 except for the absence of the peripheral restraining structure 26. Thus, the lower plate 14 has an outer surface 40 which is planar, serrated and microfinished like the outer surface 18 of the upper plate 12. The lower plate 14 optionally carries a fin 42 similar to the fin 22 of the upper plate. The inner surface 44 of the lower plate 14 is concavely, spherically curved with a radius of curvature matching that of the inner surface 24 of the upper plate 12. Once again, this surface may be provided with a titanium nitride or other finish.

(13) At the outer edge of the inner curved surface 44, the lower plate 14 is provided with an inclined ledge formation 46. Alternatively, the lower plate 14 may include peripheral restraining structure analogous to the peripheral restraining structure 26 on the upper plate 12.

(14) The core 16 of the disc 10 is at least partially made of one or more metals, alloys or a combination of metals or alloys. For example, metals used to form all or part of the core 16 may include but are not limited to cobalt chrome molybdenum, titanium (such as grade 5 titanium), stainless steel and/or the like. In some embodiments, the core 16 may be made of the same material as the upper plate 12 and the lower plate 14, which may help resist oxidation of metallic surfaces of the disc 10. In alternative embodiments, the core 16 may be made of different material(s) than the plates 12, 14. In the embodiment shown, the core 16 has identical upper and lower spherically curved convex surfaces 48, 50. At least one of the curved surfaces 48, 50 is metallic or covered in metal. In some embodiments, the entire core 16 is metallic, while in other embodiments the curved surfaces 48, 50 may be coated or laminated with metal, or one or more metallic surfaces may be otherwise attached to the core 16. In some embodiments, the core 16 is made of a polymer or ceramic, with attached metallic curved surfaces 48, 50. Alternatively, the core 16 may be a hollow metallic structure. The radius of curvature of these surfaces matches the radius of curvature of the inner surfaces 24, 44 of the upper and lower plates 12, 14. The curved surfaces are accordingly complementary.

(15) The core 16 is symmetrical about a central, equatorial plane 52 which bisects it laterally. (Although in other embodiments, the core 16 may be asymmetrical.) Lying on this equatorial plane is an annular recess or groove 54 which extends about the periphery of the core. The groove 54 is defined between upper and lower ribs or lips 56. When the plates 12, 14 and core 16 are assembled and in the orientation seen in FIG. 1, the flange 28 lies on the equatorial plane and directly aligned with the groove 54. The outer diameter 58 of the lips 56 is preferably very slightly larger than the diameter 60 defined by the inner edge of the flange 28. In some embodiments, the core 16 is movably fitted into the upper plate 12 via an interference fit. To form such an interference fit with a metal core 16 and metal plate 12, any suitable techniques may be used. For example, the plate 12 may be heated so that it expands, and the core 16 may be dropped into the plate 12 in the expanded state. When the plate 12 cools and contracts, the interference fit is created. In another embodiment, the upper plate 12 may be formed around the core 16. Alternatively, the core 16 and upper plate 12 may include complementary threads 59, 61 as shown in FIG. 1A, which allow the core 16 to be screwed into the upper plate 12, where it can then freely move.

(16) In an alternative embodiment (not shown), the outer diameter 58 of the lips 56 may be very slightly smaller than the diameter 60 defined by the inner edge of the flange 28. In such embodiments, the core 16 and the plates 12, 14 are not coupled via an interference fit but are instead coupled via forces applied by the vertebral column itself, thus acting analogously to a ball-and-socket joint.

(17) Referring now to FIG. 5, in some embodiments, the core 16 includes one or more surface channels 102 for allowing passage of fluid along the contact surfaces 104 of the core 16. Bodily fluids and/or injected fluid may pass through such a channel 102, between the core 16 and the upper and lower plates 12, 14, to promote lubrication between the contact surfaces 104 of the core and their corresponding surfaces on the upper and lower plates 12, 14. Any number, pattern, shape, depth, width or length of surface channels 102 may be included on a contact surface 104, in various embodiments. In some embodiments, for example, channels 102 may have a depth of about 3 mm or less, and more preferably about 2 mm or less, and even more preferably about 1 mm or less. Surface channels 102 may have a cross-sectional shape that is curved, rectangular, V-shaped or any other suitable shaped. Furthermore, surface channels 102 may be disposed on the contact surface(s) 104 of the core 16 in a helical pattern (as shown) or in any other suitable pattern, such as circular, rectangular, curved, one or more straight, parallel lines, two or more perpendicular lines, or the like. Surface channels 102 help prevent sticking or loss of freedom of motion (seizing) between the core 16 and the plates 12, 14 which may occur otherwise due to metal-on-metal contact.

(18) In some embodiments, one or both of the inner surfaces 24, 44 of the upper and lower plates 12, 14 may also include one or more surface channels 25, 45 as shown in FIG. 1. Again, such channels may have any suitable configuration, size, number and shape, and may assist in promoting lubrication between the core 16 and the upper and lower plates 12, 14.

(19) The central axis of the disc 10 (the axis passing through the centers of curvature of the curved surfaces) is indicated with the reference numeral 62. As shown in FIG. 1, the disc 10 may be symmetrical about a central anterior-posterior plane containing the axis 62. Referring to FIG. 4, in some embodiments the axis 62 is posteriorly disposed, i.e. is located closer to the posterior limit of the disc than the anterior limit thereof.

(20) In use, the disc 10 is surgically implanted between adjacent spinal vertebrae in place of a damaged disc. The adjacent vertebrae are forcibly separated from one another to provide the necessary space for insertion. The disc is inserted, normally in a posterior direction, into place between the vertebrae with the fins 22, 42 of the plates 12, 14 entering slots cut in the opposing vertebral surfaces to receive them. During and/or after insertion, the vertebrae, facets, adjacent ligaments and soft tissues are allowed to move together to hold the disc in place. The serrated and microfinished surfaces 18, 40 of the plates 12, 14 locate against the opposing vertebrae. The serrations 20 and fins 22, 42 provide initial stability and fixation for the disc 10. With passage of time, enhanced by the titanium surface coating, firm connection between the plates and the vertebrae will be achieved as bone tissue grows over the serrated surface. Bone tissue growth will also take place about the fins 22, 40 and through the transverse holes 23 therein, further enhancing the connection which is achieved.

(21) In the assembled disc 10, the complementary and cooperating spherical surfaces of the plates and core allow the plates to slide or articulate over the core through a fairly large range of angles and in all directions or degrees of freedom, including rotation about the central axis 62. FIGS. 1 and 4 show the disc 10 with the plates 12 and 14 and core 16 aligned vertically with one another on the axis 62. FIG. 2 illustrates a situation where maximum anterior flexion of the disc 10 has taken place. At this position, the upper rib 56 has entered the hollow 38 of the U-shaped member 30, the lower surface of the rib 56 has moved into contact with the upper surface 34 of the flange 28, the flange having moved into the groove 54, and the lower surface 36 of the flange has moved into contact with the upper surface of the ledge formation 46, as will be seen in the encircled areas 69. Abutment between the various surfaces prevents further anterior flexure. The design also allows for the inner extremity of the flange 28 to abut against the base of the groove 54, thereby limiting further relative movement between the core and plate. A similar configuration is achieved in the event of maximum posterior flexure of the plates 12, 14 over the core, such as during spinal extension and/or in the event of maximum lateral flexure.

(22) FIG. 3 illustrates how the disc 10 can also allow for translational movement of the plates relative to the core. In the illustrated situation there has been lateral translation of the plates relative to the core. The limit of lateral translation is reached when the inner extremity of the flange 28 abuts the base of the groove 54 as indicated by the numeral 70.

(23) The flange 28 and the groove 54 defined between the ribs 56, prevent separation of the core from the plates. In other words, the cooperation of the retaining formations ensures that the core is held captive between the plates at all times during flexure of the disc 10.

(24) In an alternative embodiment, the continuous annular flange 28 may be replaced by a retaining formation comprising a number of flange segments which are spaced apart circumferentially. Such an embodiment could include a single, continuous groove 54 as in the illustrated embodiment. Alternatively, a corresponding number of groove-like recesses spaced apart around the periphery of the core could be used, with each flange segment opposing one of the recesses. In another embodiment, the continuous flange or the plurality of flange segments could be replaced by inwardly directed pegs or pins carried by the upper plate 12. This embodiment could include a single, continuous groove 54 or a series of circumferentially spaced recesses with each pin or peg opposing a recess.

(25) In yet another embodiment, the retaining formation(s) could be carried by the lower plate 14 instead of the upper plate, i.e. the plates are reversed. In some embodiments, the upper (or lower) plate is formed with an inwardly facing groove, or circumferentially spaced groove segments, at the edge of its inner, curved surface, and the outer periphery of the core is formed with an outwardly facing flange or with circumferentially spaced flange segments.

(26) Although the foregoing is a complete and accurate description of the invention, any of a number of modifications, additions or the like may be made to the various embodiments without departing from the scope of the invention. Therefore, nothing described above should be interpreted as limiting the scope of the invention at it is described in the claims.