Human spinal disc prothesis with hinges

Abstract

The invention relates to a spinal disc endoprosthesis. The endoprosthesis has a resilient body formed of one or more materials which may vary in stiffness from a relatively stiff exterior annular gasket portion to a relatively supple central nucleus portion. concaval-convex elements at least partly surround that nucleus portion so as to retain the nucleus portion and gasket between adjacent vertebral bodies in a patient's spine. Assemblies of endoprosthetic discs, endoprosthetic vertebral bodies, and endoprosthetic longitudinal ligaments may be constructed. To implant this endoprosthesis assembly, information is obtained regarding the size, shape, and nature of a patient's damaged spine. Thereafter, one or more prosthetic vertebral bodies and disc units are constructed in conformity with that information. Finally, the completed and conformed vertebral body and disc assembly is implanted in the patient's spine.

Description

This is a continuation-in-part of U.S. patent application Ser. No. 08/681,230, filed Jul. 22, 1996, now U.S. Pat. No. 5,674,296 and which is a continuation-in-part of U.S. patent application Ser. No. 08/339,490, filed Nov. 14, 1994, which is abandoned.

BACKGROUND OF THE INVENTION

This invention relates generally to human prostheses, and especially to spinal column a vertebral an intervertebral disc endoprosthesis 18 is affixed between the adjacent natural vertebral bodies 12 and 14. Here this vertebral intervertebral disc endoprosthesis 18 comprises a resilient disc body 20 having a relatively stiff annular gasket exterior portion 22 and a relatively supple nuclear central portion 24. The annular gasket 22 can be formed from a suitable biocompatible elastomer in the range of approximately 70-90 durometer hardness and the nuclear central portion 24 can be formed from a softer biocompatible elastomeric polymer of approximately 30 durometer hardness. In an alternate embodiment, the gasket 22 can extend over and under the nuclear central portion 24 so as to fully enclose it within a thin layer. In a further embodiment, the nuclear central portion, the gasket, and the thin layer extension are molded together to form one piece having different durometer hardnesses.

Concaval-convex means 30 surround the resilient body 20 to retain the resilient body 20 between the adjacent natural vertebral bodies 12, 14 in a patient's spine 10. To this end, as shown in FIG. 3, the concaval-convex means 30 comprise two generally L-shaped supports 32 and 34. The supports 32, 34 each have confronting first concaval-convex legs 42, 44, each leg being of relatively constant cross-sectional thickness. Each leg 42, 44 has an outer convex surface 52, 54 for engaging the adjacent bone of the natural vertebral bodies 12, 14. Corresponding inner concave surfaces 62, 64 in confronting array retain the resilient body 20 in its illustrated compressive force shock-absorbing position. These supports 32 and 34 can undergo principle movement away from one another, but only limited secondary translational, rotational and distractional motion will occur. Each support 32, 34 has a second wing or leg 72, 74 extending generally perpendicularly to the first legs 42, 44 respectively, and adapted for affixation to the adjacent bone structure. To carry out aspects of the invention described below, this affixation is effectively accomplished by cannulated screw devices 82, 84 which may be of a biodegradable type manufactured by Zimmer of Largo, Fla. Each device 82, 84 comprises a screw 92, 94; and a screw anchor 102, 104 adapted to threadably receive the screw extends radially into and seats within the bone structure 12, 14 as especially shown in FIG. 3. The screws 92, 94 may terminate in the anchor or alternately proceed through an open ended anchor and terminate in the bone of the vertebral body 12, 14 directly. The anchors 102, 104 may be close-ended, open ended, or of the expansion type.

To discourage and prohibit migration of fluids between the endoprosthesis 18 and adjacent parts of the anatomy, a seal member 110 is attached to the supports 32, 34 so as to surround the resilient body 20 which is comprised of the gasket 22 and nucleus 24, in accordance with another aspect of the invention. Here, this seal member 110 comprises a flexible sheet material having a multiplicity of pores. Preferably, the pores are from about 5 microns to about 60 microns in size. A flexible, strong polymer sheet material from which this seal is formed can be a Kevlar-like material, or it can be Goretex-like material, expanded PTFE, or other appropriate biocompatible material, such as polyether, polyurethane, or polycarbonate urethane membranes, can be used. Kevlar material is offered by the E. I. DuPont de Nemours Company of Wilmington, Del. and Goretex material is offered by the W. T. Gore Company of Flagstaff and Phoenix, Ariz. The seal material may be lined on its interior surface, its exterior surface, or both surfaces with silicone or any suitable sealing material so as to render the flexible sheet material substantially impervious to the passage of any fluid. A watertight seal is perfected when the seal 110 is glued or otherwise affixed to the legs 42, 44 and mediate portions of the legs 72, 74 as suggested in FIGS. 1-3.

In the space beneath the seal member 110 and between the disc body 20 and the concave surfaces of legs 42, 44, a lubricant may be used. The lubricant used may be saline or an appropriate liquid or particulate material lubricant.

In an alternative embodiment, the watertight seal between the endoprosthesis 18 and adjacent parts of the anatomy can be provided by developing a groove 402 completely encircling the periphery of each of the legs 42, 44. In this embodiment, the legs 72, 74 may be attached to the circumferential groove member 402 by laser-welding or other suitable means. If the legs 72, 74 are of polymeric material, they may be attached by mechanical or adhesive techniques. Only one of the grooves is shown in FIG. 13. In this embodiment, the seal member 410 is provided with a beaded edge 412 for each groove. Additionally, a retaining band 415 is provided for each groove to retain the seal member 410 in groove 402. The retaining bands 415 can be in the form of a biocompatible monofilament wire of, for example, stainless steel or titanium, a synthetic polymer cable or a braided wire cable. As shown in FIG. 11, each retaining band is crimped anteriorly by a crimping sleeve 420. Of course, more than one crimping sleeve may be used, if necessary. Alternately, the retaining band is fastened by laser-welding. Although one sealing arrangement consisting of the groove, beaded edge and retaining band is shown in FIG. 14, it should be understood that the sealing arrangement on the concaval-convex leg of the other support is identical in design and function.

In use, the seal member 410 is placed about the concaval-convex means 30. The retaining bands 415 are then placed adjacent to the respective groove 402 and crimped anteriorly, thereby fitting the bands into the grooves. Each beaded edge 412 prevents the slipping of the seal member underneath the retaining band. Thus, the retaining band, the groove and the beaded edge all cooperate to provide a water-tight seal to prevent the migration of fluids between the endoprosthesis 18 and adjacent parts of the anatomy. Glue can also be used to affix the seal member to the concaval-convex means 30 as a supplemental means for perfecting the seal.

In a first embodiment, the first legs 42, 44 are formed as an integral piece with the respective second wings or legs 72, 74. In the alternate embodiment of FIG. 3, however, the first legs 42, 44 are hingedly attached to the respective second legs 72, 74. A hinge 43, 73 is provided at the point from which the second leg 72, 74 extends generally perpendicularly to the first leg 42, 44. The hinge is not intended to function as such after being installed, but only during installation so as to allow better alignment of the endoprosthesis with the biologically variable anterior surface of the respective vertebral body. Once the endoprosthesis is installed and affixed via the screw devices, the hinge will no longer move.

These hinges 43, 73 may take any of the several known forms. Each hinge can be a rod and socket hinge, a pin type hinge, or a slip joint fitting, or it can be a web or a membrane type hinge of metal or plastic.

The second wings or legs 72, 74 may be made of a suitable metal such as titanium or a polymeric material. Alternately, each leg 72, 74 including its associated hinge element, can be made of a biodegradable polymeric material. When the legs 72, 74 are made of biodegradable material, the screws 92, 94 used for affixing the legs to the adjacent bone structure may be of the standard shoulder screw type in order to maintain firm fixation to the screw anchors 102, 104 after biodegradation of the legs 72, 74.

Legs 72, 74 can be of a thin construction that allows some degree of flexibility so as to promote a better mating of the legs to the anterior aspect of the vertebral body 12, 14.

The legs can have a central closed oblong slot to accommodate a screw or other fixation device. Should a second endoprosthesis device be placed at an adjoining level, the leg 72, 74 would be placed on top of the corresponding leg from the adjacent device. The screw 92, 94 or other fixation device would then pass through the closed oblong slot of the overlapping legs 72, 74.

In accordance with another aspect of the invention, the supports 32, 34 are formed of a biocompatible metal which may contain chromium cobalt or titanium. Surface roughening or titanium beading 112, 114 on the exterior surfaces 52, 54 of legs 42, 44 encourages positive bonding between the adjacent bone and the convex surfaces 52, 54. Over time, bone fuses or grows into the surface roughening, thereby adhering to the legs 42, 44 in a rigid and strong manner.

As suggested in FIGS. 9 and 10, a prosthetic longitudinal ligament 250 can be connected between the screws 92, 94 to limit motions between elements of the spine 10 in the area where the endoprosthesis 18 is implanted. This strap 250 may be made of the Kevlar-like material or the Goretex-like material described above, or it may be made of any other strong biocompatible material. The ligament 250 may also be considered a spacer or cover for providing some degree of separation between overlying soft tissues in the body and the anterior-most surfaces of the device. However, it is not designed for restricting or preventing motion in the disc body. A biodegradable washer can be provided around the screws 92, 94 at a point between the strap 250 and the respective wing or leg 72, 74. When biodegradable washers are used, the screws 92, 94 used for affixing the legs to the adjacent bone structure may be of the standard shoulder screw type in order to maintain firm fixation to the screw anchors 102, 104 after biodegradation of the washers.

When a ligament is used in the embodiment of the device having hinged legs 92, 94, the prosthetic longitudinal ligament structure can comprise several parallel bands of material separated by approximately 10 mm.

In accordance with another aspect of the invention, multiple endoprosthetic disc units can be placed in series with a straddling interlock appendage providing stability and fixation as shown in FIG. 5. Entire portions of a patient's spine can be replaced by a series of interconnected endoprosthetic vertebral bodies and endoprosthetic disc units. FIGS. 6-8 show an upper natural vertebral body unit 312 to which an upper endoprosthetic body 308 has been attached. A lower natural vertebral body 314 has attached, at its upper end, an endoprosthetic disc unit 318. Between these endoprosthetic disc units 308 and 318 is an endoprosthetic vertebral body 320. As suggested by FIG. 7, the endoprosthetic vertebral body 320 need not be irregularly shaped in cross sectional aspect; rather, manufacturing processes may suggest that it have a circular cross-sectional shape. As show in FIGS. 6 and 8, this endoprosthetic vertebral body 320 comprises a titanium element 321, to which are attached the preformed upper and lower endoprosthetic vertebral body upper and lower concaval-convex elements 322, 324. Each concaval-convex element 322, 324 is attached to the prosthetic vertebral body 320, as shown in FIG. 7, by extending set screws 330 through the titanium vertebral body 321 into a stem-like projection 331 extending from each of the concaval-convex elements 322, 324. A hole 360 in the body 320 accommodates the stem-like projections 331 of the concaval-convex elements 322 and 324. The stem-like projection 331 of the concaval-convex elements 322 and 324 is used only in conjunction with a prosthetic vertebral body implant construction 320.

An ear 340 is affixed, as by weldments 341, to a leg 342 extending from a concaval-convex element 322 as illustrated in FIGS. 6 and 8. An anchor 352 can be threaded into the endoprosthetic vertebral body 320, and a screw 362 can be turned into the anchor 352 so as to rigidly assemble the leg 342 to a leg 354 extending from the lower endoprosthetic disc unit 318.

In an alternate embodiment, ear 340 could be replaced with a biodegradable washer around each of the screws 92, 94 at a point located between the strap 250 and the respective leg 72, 74. (FIG. 10.) The washer could be of a size to overlie and fix in place the interlocking wing leg from the adjacent intervertebral disc space. Alternately, ear 340 (FIG. 8.) may be eliminated in favor of screws 92, 94 having a head of increased diameter so that the screw head engages and fixes both the slotted leg 72, 74 and the interlocking tongue leg.

The upper disc endoprosthesis 308, the endoprosthetic vertebral body 320, and the lower disc endoprosthesis 318 can all be assembled and interconnected as a unit before implantation in a patient's body when indicated.

As also suggested in FIG. 6, the annular corners 372, 374 of natural vertebral bodies 312, 314 each can extend irregularly radially outwardly of the adjacent disc endoprosthesis 308, 318. However, the corners 382B, 384B of the prosthetic vertebral body 320 do not generally extend significantly outside those disc units 308, 318, thus discouraging vertebral body engagement with and consequent abrasion or other damage to adjacent portions of the patient's natural anatomy. Preferably the endoprosthetic vertebral body 320 is not exactly right cylindrical in shape, but is rather slightly biconical; that is, the endoprosthetic vertebral body 320 has a waist 390 of minimum radius R at an axial medial point as suggested in FIG. 6.

According to yet another aspect of the invention, novel surgical procedures permit effective and permanent installation of the endoprosthetic vertebral body 320 and associated parts. First, a surgeon or medical technician develops information about the size, shape and nature of a patient's damaged vertebral body or bodies from radiographs, CT and/or MRI scans, noting specifically the anterior-posterior and lateral dimensions of the end plate of each involved vertebral body and the vertical height of the anterior aspect of each involved vertebral and/or proximate vertebral body and vertical height of the mid portion of involved and proximate relatively normal intervertebral disc spaces. This information is transmitted by telephone, computer datalink or documentary transport to a specialized laboratory. That laboratory constructs one or more prosthetic assemblies of the sort shown in FIG. 6 in conformity with the received information and this disclosure. Each of the assemblies can include a prosthetic vertebral body 321, and at each body end is a prosthetic disc 308, 318. Each prosthetic disc unit comprises, in turn, the concaval-convex elements 30; the resilient body 20 interposed between the concaval-convex elements; and the seal unit 110 secured around the interior legs and resilient body. Thereafter, the completed and conformed assembly is implanted in the patient's spine 10.

When the unit or units have been received and the patient properly prepared, the damaged natural spinal disc or discs and vertebral body or bodies are removed and the adjacent spinal bone surfaces are milled or otherwise formed to provide concave surfaces to receive the confronting convex surfaces 52, 54. Thereafter, the disc units and vertebral body are installed in the patient's spine.

To accurately locate the concaval-convex surfaces in the patient's spine, holes 382A, 384A (FIG. 3) are precisely located and then formed in the bone structure using a measuring instrument centered in the evacuated natural intravertebral intervertebral disc space. These holes are then tapped to form female threads therein. When the threads have been formed, the anchors 102, 104 are implanted in the respective tapped holes, thereby creating an imaginary platform of reference points located precisely with respect to the patient's spine. After the holes have been formed and the anchors 102, 104 implanted, a bone surface milling jig (not shown) is affixed to the anchors 102, 104 and the desired concave surfaces of predetermined shape are formed on the inferior and superior surfaces of the opposing vertebral bodies using one of a selection of predetermined milling head or bit sizes. Thereafter, the bone milling jig is removed and the concaval-convex elements 52, 54 identical in shape to the milled surfaces 112, 114 are inserted between the distracted milled vertebral bodies 12, 14. The distraction device is then moved. The concaval-convex structures are then attached by the same anchors 102, 104 to the bone, thus insuring a precise and stable mate between the bone surfaces and the convex surfaces 52, 54.

If necessary, a damaged implanted nucleus and/or gasket 24 can be removed and replaced. This can be accomplished by slitting the seal 110; removing the annular gasket 24 and damaged nucleus 22, and replacing them with new, undamaged elements. Thereafter, the seal 110 can be re-established by suturing or gluing closed the slit seal.

Claims

1. A vertebral An intervertebral disc endoprosthesis, comprising a resilient body formed of materials varying in stiffness from a relatively stiff exterior portion to a relatively supple central portion; and concaval-convex elements at least partly surrounding the resilient body for retaining said resilient body in a position between the concaval-convex elements, and wherein said concaval-convex elements each comprise generally l-shaped supports, each support having a first concaval-convex leg, the first leg having an outer convex surface for engaging adjacent bone and a corresponding inner concave surface for retaining the resilient body, each support further having a second leg extending generally perpendicularly to the first leg and adapted for affixation to adjacent bone structures.

2. A vertebral An intervertebral disc endoprosthesis according to claim 1 wherein said resilient body comprises an annular gasket and a nuclear central portion.

3. A vertebral An intervertebral disc endoprosthesis according to claim 2 wherein the gasket extends about the nuclear central portion to enclose it within a thin layer.

4. A vertebral An intervertebral disc endoprosthesis according to claim 3 wherein the gasket, and the nuclear central portion, and the thin layer are molded together as one piece.

5. A vertebral An intervertebral disc endoprosthesis according to claim 1 further comprising cannulated screw means for attaching the concaval-convex element supports to adjacent bone structure.

6. A vertebral An intervertebral disc endoprosthesis according to claim 5 wherein said cannulated screw means comprises a screw, and a screw anchor seatable within bone structure and adapted to threadably receive the screw.

7. A vertebral An intervertebral disc endoprosthesis according to claim 6 wherein the screws terminate in the anchor.

8. A vertebral An intervertebral disc endoprosthesis according to claim 6 wherein the anchor has an open end and the screw proceeds through the open end of the anchor and terminates in the bone of the vertebral body.

9. A vertebral An intervertebral disc endoprosthesis according to claim 1 further comprising a seal member attached to the concaval-convex elements and surrounding said resilient body.

10. A vertebral An intervertebral disc endoprosthesis according to claim 9 wherein said seal member comprises a flexible sheet material having a multiplicity of pores, the pores being from about 5 microns to about 60 microns in size.

11. A vertebral An intervertebral disc endoprosthesis according to claim 10 further including sealing means applied to said flexible sheet material to render said flexible sheet material substantially impervious to the passage of any fluid.

12. A vertebral An intervertebral disc endoprosthesis according to claim 11 wherein the sealing means is silicone.

13. A vertebral An intervertebral disc endoprosthesis according to claim 9 wherein said concaval-convex elements and said seal member collectively surround said resilient body with a watertight seal.

14. A vertebral An intervertebral disc endoprosthesis according to claim 2 wherein said annular gasket is relatively stiff and said nuclear central portion is relatively supple.

15. A vertebral An intervertebral disc endoprosthesis according to claim 1 wherein at least one of the second legs is hingedly attached to the respective first concaval-convex leg.

16. A vertebral An intervertebral disc endoprosthesis, comprising a resilient body formed of materials varying in stiffness from a relatively stiff exterior portion to a relatively supple central portion; and concaval-convex elements at least partly surrounding the resilient body between adjacent vertebral bodies for retaining the resilient body between adjacent vertebral bodies in a patient's spine, and wherein said concaval-convex elements each comprise generally l-shaped supports, each support having a first concaval-convex leg, the first leg having an outer convex surface for engaging adjacent bone and a corresponding inner concave surface for retaining the resilient body, each support further having a second leg extending generally perpendicularly to the first leg and adapted for affixation to adjacent bone structure, wherein at least the second leg is constructed of titanium.

17. A vertebral An intervertebral disc endoprosthesis comprising a resilient nucleus, first and second rigid concaval-convex elements at least partly surrounding the nucleus, first and second legs formed, respectively, with the first and second rigid concaval-convex elements, first and second means for affixing the respective legs to vertebral bodies adjacent the concaval-convex elements and nucleus, longitudinal ligament prosthesis means extending between the legs of the first and second concaval-convex elements to inhibit undesirable motion of the vertebral bodies relative to one another, and biodegradable washers positioned between the ligament prosthesis means and the respective legs.

18. A vertebral An intervertebral disc endoprosthesis comprising a rounded, resilient nucleus body convex on all surfaces and concaval-convex elements, each concaval-convex element being of relatively constant cross-sectional thickness and having an outer convex surface for engaging adjacent bone structure which has been milled to mate with the concaval-convex element outer convex surface, and a corresponding inner concave surface for engaging the rounded resilient body, wherein lubricant is provided between the nucleus body and the concaval-convex elements.

19. A vertebral An intervertebral endoprosthesis comprising an integral disc unit, said unit including a pair of confronting l-shaped supports having concaval-convex shapes in given legs, a resilient body interposed between the supports, and a flexible seal extending from one support to the other and sealing the resilient body within the supports inside a substantially watertight compartment, further comprising a plurality of said integral disc units.

20. The vertebral intervertebral disc endoprosthesis according to claim 19 wherein each support includes a groove about its circumference.

21. The intervertebral disc endoprosthesis according to claim 13, wherein the seal member comprises a flexible sheet secured to each of the concaval-convex elements.

22. The intervertebral disc endoprosthesis according to claim 19, further comprising a plurality of said integral disc units.