USRE42480E1 - Human spinal disc prothesis with hinges - Google Patents

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 vertebral intervertebral disc prostheses. The invention also relates to surgical procedures for preparing the patient to receive a vertebral an intervertebral disc endoprosthesis, and for implanting that endoprosthesis in the patient's spine.

The herniation of a spinal disc and the often resultant symptoms of intractable pain, weakness, sensory loss, incontinence and progressive arthritis are among the most common of debilitating processes affecting mankind. If a patient's condition does not improve after conservative treatment, and if clear physical evidence of nerve root or spinal cord compression is apparent, and if correlating radiographic studies (i.e., MRI or CT imaging or myelography) confirm the condition, surgical removal of the herniated disc may be indicated. The process of discectomy—as the name implies—involves the simple removal of the disc without attempt to replace or repair the malfunctioning unit. In the United States in 1985, over 250,000 such operations were performed in the lumbar spine and in the cervical spine.

Statistics suggest that present surgical techniques are likely to result in short-term relief, but will not prevent the progressive deterioration of the patient's condition in the long run. Through better pre-operative procedures and diagnostic studies, long-term patient results have improved somewhat. But it has become clear that unless the removed disc is replaced or the spine is otherwise properly supported, further degeneration of the patient's condition will almost certainly occur.

In the mid-1950's and 60's, Cloward and Smith & Robinson popularized anterior surgical approaches to the cervical spine for the treatment of cervical degenerative disc disease and related disorders of the vertebrae, spinal cord and nerve root; these surgeries involved disc removal followed by interbody fusion with a bone graft. It was noted by Robinson (Robinson, R. A.: The Results of Anterior Interbody Fusion of the Cervical Spine, J. Bone Joint Surg., 440A: 1569-1586, 1962) that after surgical fusion, osteophyte (bone spur) reabsorption at the fused segment might take place. However, it has become increasingly apparent that unfused vertebral segments at the levels above and below the fused segment degenerate at accelerated rates as a direct result of this fusion. This has led some surgeons to perform discectomy alone, without fusion, by a posterior approach in the neck of some patients. However, as has occurred in surgeries involving the lower back where discectomy without fusion is more common as the initial treatment for disc herniation syndromes, progressive degeneration at the level of disc excision is the rule rather than the exception. Premature degenerative disc disease at the level above and below the excised disc can and does occur.

Spine surgery occasionally involves fusion of the spine segments. In addition to the problems created by disc herniation, traumatic, malignant, infectious and degenerative syndromes of the spine can be treated by fusion. Other procedures can include bone grafts and heavy duty metallic rods, hooks, plates and screws being appended to the patient's anatomy; often they are rigidly and internally fixed. None provide for a patient's return to near-normal functioning. Though these procedures may solve a short-term problem, they can cause other, longer term, problems.

A number of attempts have been made to solve some of the problems described above by providing a patient with spinal disc prostheses, or artificial discs of one sort or another. For example, Steffee, U.S. Pat. No. 5,031,437, describes a spinal disc prosthesis having upper and lower rigid flat plates and a flat elastomeric core sandwiched between the plates. Frey et al., U.S. Pat. Nos. 4,917,704 and 4,955,908, disclose intervertebral prostheses, but the prostheses are described as solid bodies.

U.S. Pat. Nos. 4,911,718 and 5,171,281 disclose resilient disc spacers, but no inter-connective or containing planes or like elements are suggested, and sealing the entire unit is not taught.

It is the primary aim of the present invention to provide a vertebral an intervertebral disc endoprosthesis which will perform effectively and efficiently within a patient's spine over a long period of time, and which will not encourage degeneration of or cause damage to adjacent natural disc parts.

It is a related objective to provide a new vertebral intervertebral disc endoprosthesis surgical procedure which will decrease post-operative recovery time and inhibit post-operative disc, vertebral body and spinal joint degeneration.

It is yet another object to provide a method of installing the endoprosthesis so as to accurately mate the endoprosthesis with an adjacent specifically formed bone surface. An associated object is to provide an endoprosthesis which will encourage bone attachment to, and growth upon, adjacent outer surfaces of the endoprosthesis.

Yet another object is to provide a vertebral endoprosthesis in which the parts are non-oncogenic.

Still another object is to provide a vertebral an intervertebral disc endoprosthesis having a resilient element to accommodate shocks and other forces applied to the spine.

Another object is to provide a highly effective vertebral endoprosthesis which includes several disc endoprostheses and one or more prosthetic vertebral bodies. A related object is to provide these elements in a pre-assembled array for implantation in a patient.

SUMMARY OF THE INVENTION

To accomplish these objects, the invention comprises a resilient body formed of a material varying in stiffness from a relatively stiff exterior portion to a relatively supple central portion. A concaval-convex means at least partly surrounds that resilient body so as to retain the resilient body between adjacent vertebral bodies of a patient's spine. If medical considerations so indicate, several disc endoprostheses can be combined with one or more endoprosthetic vertebral bodies in an entire assembly.

To implant this endoprosthesis assembly, information is obtained regarding the size, shape, and nature of a patient's damaged natural spinal discs. If one or more of the patient's vertebral bodies also require replacement, information about those bodies is also obtained. Thereafter, one or more prosthetic disc units and interposed prosthetic vertebral body units are constructed and preassembled in conformity with that information. Finally, the completed and conformed prosthetic disc and vertebral body assembly is implanted in the patient's spine.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary vertical view of a portion of a human spine in which is installed a novel vertebral disc endoprosthesis embodying the present invention;

FIG. 2 is a fragmentary side elevational view similar toFIG. 1 showing the elements of a patient's spine and having a novel vertebral disc endoprosthesis embodying the present invention installed therein;

FIG. 3 is a sectional view taken substantially in the plane of line3-3 inFIG. 1;

FIG. 4 is an exploded view of the novel vertebral disc endoprosthesis;

FIG. 5 is a vertical fragmentary view of a patient's spine similar toFIG. 1, but showing a series of novel disc endoprosthesis units installed in the spine and interconnected to one another;

FIG. 6 is a fragmentary sectional view of a patient's spine similar toFIG. 3 and taken along line6-6 inFIG. 5, but showing a natural upper vertebral body, and upper endoprosthetic disc; an adjacent endoprosthetic vertebral body; a second or lower endoprosthetic disc; and a second or lower natural vertebral body;

FIG. 7 is a sectional view taken substantially in the plane of line7-7 ofFIG. 6;

FIG. 8 is a fragmentary side elevational view of the assembly shown inFIG. 6; and

FIG. 9 is a fragment vertical view, similar toFIG. 1, of a portion of a human spine in which is installed a variant form of the novel vertebral disc endoprosthesis the variant form having a prosthetic longitudinal ligament;

FIG. 10 is a sectional view taken substantially in the plane of line10-10 inFIG. 9;

FIG. 11 is a top view of a retainer means for use with a vertebral disc endoprosthesis;

FIG. 12 is a sectional view taken substantially in the plane of line12-12 ofFIG. 11;

FIG. 13 is a side view of a vertebral disc endoprosthesis having a groove for receiving the retainer means; and

FIG. 14 is a cross-sectional view of the retainer means in use.

DETAILED DESCRIPTION

While the invention will be described in connection with a preferred embodiment and procedure, it will be understood that it is not intended to limit the invention to this embodiment or procedure. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Turning more specifically toFIGS. 1-3, a portion of ahuman spine10 is shown. The illustratedspine10 has been subjected to a discectomy surgical process. To discourage degeneration of or damage to the naturalvertebral bodies12 and14 and their respective facet joints, in accordance with the invention, a vertebral anintervertebral disc endoprosthesis18 is affixed between the adjacent naturalvertebral bodies12 and14. Here this vertebralintervertebral disc endoprosthesis18 comprises aresilient disc body20 having a relatively stiff annulargasket exterior portion22 and a relatively supple nuclearcentral portion24. Theannular gasket22 can be formed from a suitable biocompatible elastomer in the range of approximately 70-90 durometer hardness and the nuclearcentral portion24 can be formed from a softer biocompatible elastomeric polymer of approximately 30 durometer hardness. In an alternate embodiment, thegasket22 can extend over and under the nuclearcentral portion24 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 means30 surround theresilient body20 to retain theresilient body20 between the adjacent naturalvertebral bodies12,14 in a patient'sspine10. To this end, as shown inFIG. 3, the concaval-convex means30 comprise two generally L-shapedsupports32 and34. The supports32,34 each have confronting first concaval-convex legs42,44, each leg being of relatively constant cross-sectional thickness. Eachleg42,44 has an outerconvex surface52,54 for engaging the adjacent bone of the naturalvertebral bodies12,14. Corresponding innerconcave surfaces62,64 in confronting array retain theresilient body20 in its illustrated compressive force shock-absorbing position. These supports32 and34 can undergo principle movement away from one another, but only limited secondary translational, rotational and distractional motion will occur. Eachsupport32,34 has a second wing orleg72,74 extending generally perpendicularly to thefirst legs42,44 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 cannulatedscrew devices82,84 which may be of a biodegradable type manufactured by Zimmer of Largo, Fla. Eachdevice82,84 comprises ascrew92,94; and ascrew anchor102,104 adapted to threadably receive the screw extends radially into and seats within thebone structure12,14 as especially shown inFIG. 3. Thescrews92,94 may terminate in the anchor or alternately proceed through an open ended anchor and terminate in the bone of thevertebral body12,14 directly. Theanchors102,104 may be close-ended, open ended, or of the expansion type.

To discourage and prohibit migration of fluids between theendoprosthesis18 and adjacent parts of the anatomy, aseal member110 is attached to thesupports32,34 so as to surround theresilient body20 which is comprised of thegasket22 andnucleus24, in accordance with another aspect of the invention. Here, thisseal member110 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 theseal110 is glued or otherwise affixed to thelegs42,44 and mediate portions of thelegs72,74 as suggested inFIGS. 1-3.

In the space beneath theseal member110 and between thedisc body20 and the concave surfaces oflegs42,44, 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 theendoprosthesis18 and adjacent parts of the anatomy can be provided by developing agroove402 completely encircling the periphery of each of thelegs42,44. In this embodiment, thelegs72,74 may be attached to thecircumferential groove member402 by laser-welding or other suitable means. If thelegs72,74 are of polymeric material, they may be attached by mechanical or adhesive techniques. Only one of the grooves is shown inFIG. 13. In this embodiment, theseal member410 is provided with abeaded edge412 for each groove. Additionally, a retainingband415 is provided for each groove to retain theseal member410 ingroove402. The retainingbands415 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 inFIG. 11, each retaining band is crimped anteriorly by a crimpingsleeve420. 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 inFIG. 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, theseal member410 is placed about the concaval-convex means30. The retainingbands415 are then placed adjacent to therespective groove402 and crimped anteriorly, thereby fitting the bands into the grooves. Eachbeaded edge412 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 theendoprosthesis18 and adjacent parts of the anatomy. Glue can also be used to affix the seal member to the concaval-convex means30 as a supplemental means for perfecting the seal.

In a first embodiment, thefirst legs42,44 are formed as an integral piece with the respective second wings orlegs72,74. In the alternate embodiment ofFIG. 3, however, thefirst legs42,44 are hingedly attached to the respectivesecond legs72,74. Ahinge43,73 is provided at the point from which thesecond leg72,74 extends generally perpendicularly to thefirst leg42,44. 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 hinges43,73 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 orlegs72,74 may be made of a suitable metal such as titanium or a polymeric material. Alternately, eachleg72,74 including its associated hinge element, can be made of a biodegradable polymeric material. When thelegs72,74 are made of biodegradable material, thescrews92,94 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 anchors102,104 after biodegradation of thelegs72,74.

Legs72,74 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 thevertebral body12,14.

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, theleg72,74 would be placed on top of the corresponding leg from the adjacent device. Thescrew92,94 or other fixation device would then pass through the closed oblong slot of the overlappinglegs72,74.

In accordance with another aspect of the invention, thesupports32,34 are formed of a biocompatible metal which may contain chromium cobalt or titanium. Surface roughening ortitanium beading112,114 on the exterior surfaces52,54 oflegs42,44 encourages positive bonding between the adjacent bone and theconvex surfaces52,54. Over time, bone fuses or grows into the surface roughening, thereby adhering to thelegs42,44 in a rigid and strong manner.

As suggested inFIGS. 9 and 10, a prostheticlongitudinal ligament250 can be connected between thescrews92,94 to limit motions between elements of thespine10 in the area where theendoprosthesis18 is implanted. Thisstrap250 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. Theligament250 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 thescrews92,94 at a point between thestrap250 and the respective wing orleg72,74. When biodegradable washers are used, thescrews92,94 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 anchors102,104 after biodegradation of the washers.

When a ligament is used in the embodiment of the device having hingedlegs92,94, 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 inFIG. 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 naturalvertebral body unit312 to which an upperendoprosthetic body308 has been attached. A lower naturalvertebral body314 has attached, at its upper end, anendoprosthetic disc unit318. Between theseendoprosthetic disc units308 and318 is an endoprostheticvertebral body320. As suggested byFIG. 7, the endoprostheticvertebral body320 need not be irregularly shaped in cross sectional aspect; rather, manufacturing processes may suggest that it have a circular cross-sectional shape. As show inFIGS. 6 and 8, this endoprostheticvertebral body320 comprises atitanium element321, to which are attached the preformed upper and lower endoprosthetic vertebral body upper and lower concaval-convex elements322,324. Each concaval-convex element322,324 is attached to the prostheticvertebral body320, as shown inFIG. 7, by extending setscrews330 through the titaniumvertebral body321 into a stem-like projection331 extending from each of the concaval-convex elements322,324. Ahole360 in thebody320 accommodates the stem-like projections331 of the concaval-convex elements322 and324. The stem-like projection331 of the concaval-convex elements322 and324 is used only in conjunction with a prosthetic vertebralbody implant construction320.

Anear340 is affixed, as byweldments341, to aleg342 extending from a concaval-convex element322 as illustrated inFIGS. 6 and 8. Ananchor352 can be threaded into the endoprostheticvertebral body320, and ascrew362 can be turned into theanchor352 so as to rigidly assemble theleg342 to aleg354 extending from the lowerendoprosthetic disc unit318.

In an alternate embodiment,ear340 could be replaced with a biodegradable washer around each of thescrews92,94 at a point located between thestrap250 and therespective leg72,74. (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, ear340 (FIG. 8.) may be eliminated in favor ofscrews92,94 having a head of increased diameter so that the screw head engages and fixes both the slottedleg72,74 and the interlocking tongue leg.

Theupper disc endoprosthesis308, the endoprostheticvertebral body320, and thelower disc endoprosthesis318 can all be assembled and interconnected as a unit before implantation in a patient's body when indicated.

As also suggested inFIG. 6, theannular corners372,374 of naturalvertebral bodies312,314 each can extend irregularly radially outwardly of theadjacent disc endoprosthesis308,318. However, the corners382B,384B of the prostheticvertebral body320 do not generally extend significantly outside thosedisc units308,318, thus discouraging vertebral body engagement with and consequent abrasion or other damage to adjacent portions of the patient's natural anatomy. Preferably the endoprostheticvertebral body320 is not exactly right cylindrical in shape, but is rather slightly biconical; that is, the endoprostheticvertebral body320 has awaist390 of minimum radius R at an axial medial point as suggested inFIG. 6.

According to yet another aspect of the invention, novel surgical procedures permit effective and permanent installation of the endoprostheticvertebral body320 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 inFIG. 6 in conformity with the received information and this disclosure. Each of the assemblies can include a prostheticvertebral body321, and at each body end is aprosthetic disc308,318. Each prosthetic disc unit comprises, in turn, the concaval-convex elements30; theresilient body20 interposed between the concaval-convex elements; and theseal unit110 secured around the interior legs and resilient body. Thereafter, the completed and conformed assembly is implanted in the patient'sspine10.

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 confrontingconvex surfaces52,54. 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, holes382A,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, theanchors102,104 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 theanchors102,104 implanted, a bone surface milling jig (not shown) is affixed to theanchors102,104 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 elements52,54 identical in shape to the milledsurfaces112,114 are inserted between the distracted milledvertebral bodies12,14. The distraction device is then moved. The concaval-convex structures are then attached by thesame anchors102,104 to the bone, thus insuring a precise and stable mate between the bone surfaces and theconvex surfaces52,54.

If necessary, a damaged implanted nucleus and/orgasket24 can be removed and replaced. This can be accomplished by slitting theseal110; removing theannular gasket24 and damagednucleus22, and replacing them with new, undamaged elements. Thereafter, theseal110 can be re-established by suturing or gluing closed the slit seal.

Claims (22)

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 toclaim 1 wherein said resilient body comprises an annular gasket and a nuclear central portion.

3. A vertebral An intervertebral disc endoprosthesis according toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 6 wherein the screws terminate in the anchor.

8. A vertebral An intervertebral disc endoprosthesis according toclaim 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 toclaim 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 toclaim 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 toclaim 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 toclaim 11 wherein the sealing means is silicone.

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

15. A vertebral An intervertebral disc endoprosthesis according toclaim 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 toclaim 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.

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