HK1098338A - Flexible spinal disc - Google Patents

Description

Flexible spinal disc

Technical Field

The present invention relates to a prosthetic spinal disc. In particular, the present invention relates to an implantable artificial spinal disc made of a strong elastomer capable of functioning as a normal spinal disc.

Background

The spine is composed of bony structures called vertebral bodies separated by soft tissue structures called intervertebral discs. The intervertebral disc is commonly referred to as the spinal disc. The spinal disc acts primarily as a mechanical cushion between the vertebrae to allow controlled movement between the vertebral segments of axial bone. The spinal disc acts as a joint, allowing physiological degrees of flexion, extension, lateral bending, and pivoting. The mechanical properties of the disc must be capable of these actions and have sufficient elastic strength to resist the external forces and torques caused by the vertebrae.

A normal spinal disc is a mixed vascular structure comprising two vertebral end plates (end plates), the annulus fibrosis (annulus), and the nucleus pulposus (nucleus). The end plates comprise thin cartilage covering a thin layer of hard cortical bone attached to the spongy cancellous bone of the vertebral body. The end plates are used to connect adjacent vertebrae to the spinal disc.

The annulus of the spinal disc is a tough, outer annulus that is about 10 to 15 millimeters in height and about 15 to 20 millimeters in thickness. The structure of the fiber is similar to that of an automobile tire, with 15 to 20 overlapping layers, and inserted into the upper and lower vertebral bodies at approximately 30-40 degrees in both directions. This configuration is particularly resistant to torque because approximately half of the angled fibers will be taut when the vertebrae are rotated in either direction relative to each other. The adhesion of the laminates to each other is somewhat weaker. The connected fibers also prevent lateral extrusion of the spinal disc when complex torsional motion of the spine occurs.

Inside the annulus fibrosus is a gelatinous nucleus pulposus with a high water content. The nucleus pulposus acts as a liquid to equalize the pressure within the annulus fibrosus. The consistency and shape of this material is similar to the inside of a jelly donut. The soft nature of the nucleus pulposus like a fluid allows it to contract when subjected to compressive forces and expand under the influence of osmotic pressure. The ion concentration of the nucleus pulposus is capable of generating an osmotic swelling pressure of about 0.1 to 0.3 megapascals. Thus, the gelatinous nucleus pulposus is able to support an applied load like a hydraulic crane. The annulus and nucleus together support the spine, which flexes when bent, lifted, due to forces generated by the adjacent vertebral bodies.

The compressive load on the spinal disc varies with posture. The compressive load of the third lumbar disc is 300 newtons (N) when the person is supine, and rises to 700 newtons when assuming an upright posture. When the body is bent forward only 20 degrees, the compressive load rises again to 1200 newtons.

Spinal discs may become displaced or damaged due to trauma or disease. When the annulus fibers weaken or tear, the inner material of the nucleus may permanently bulge, bulge or extrude out of its normal inner annulus and disc herniation may occur. Herniated or "slipped" nucleus pulposus tissue can compress the spinal nerves, resulting in leg pain, impaired muscle strength and control, and even paralysis. Alternatively, as the disc degrades, the nucleus loses its water binding capacity and contracts, resulting in a reduction in disc height. The nucleus pulposus then has reduced volume, resulting in wrinkling of the annulus at the loosely bonded portions of the laminate. When these overlapping layers of the annulus fibrosus crinkle and separate, circumferential or radial tearing of the annulus fibrosus may occur, with the result that persistent back pain may result. The adjacent secondary facet joints will also be forced into an overlapping position causing additional back pain. The most common site of occurrence of a spinal disc herniation is in the lower lumbar region. Cervical spinal discs are also often affected.

There are currently essentially three treatments for disc herniation or degeneration: conservative care, discectomy, and fusion. Most patients with lower back pain can recover through conservative treatment of bed rest.

Discectomy can provide excellent short-term results. However, discectomy is not optimal from a long-term biomechanical point of view. When a spinal disc protrusion is surgically removed, the spinal disc space will narrow and may lose its normal stability. Loss of disc height may result in osteoarthritis changes in the facet joints over time. The joint loses normal mobility and creates high stresses on the adjacent discs. Sometimes, normal disc height must be restored after the damaged disc is destroyed.

Fusion is a procedure in which two vertebral bodies are fixed to each other by a rigid metal block, usually using screws and plates. The current treatment is to maintain the disc space by inserting a metal device and bone fragments that can join the two vertebral bodies. This device is similar to a screwed healing plate, which can be usedOne vertebral body to the other. Alternatively, a hollow metal cylinder filled with bone fragments may be placed in the intervertebral space to join the vertebral bodies together (e.g., LT-Cage manufactured by Sofamor-Danek)^TMOr Lumbar I/F CAGE produced by DePuy^TM). These devices have a number of disadvantages for the patient because the bone is integrated into a rigid body that does not have the flexibility or shock absorbing properties of the natural spinal discs.

Fusion surgery generally has a better effect in eliminating pain symptoms and stabilizing joints. However, since the segments are fixed, their range of motion and the forces acting on the adjacent disc are increased, potentially accelerating the degeneration process. In the past, fusion procedures have also been used in the knee joint; however, with the advent of active total knee prosthesis, this treatment is not favored.

Some recent devices have attempted to enable movement between vertebral bodies through metal and hard plastic devices that allow some degree of relative slippage between the components (e.g., ProDisk, Charite, see U.S. Pat. nos. 5,314,477, 4,759,766, 5,401,269 and 5,556,431). The rigid parts of these devices allow some relative movement to occur but do not absorb shock.

Recently, several prosthetic spinal disc nucleus devices have been proposed. These devices fit in the space of the herniated nucleus pulposus and require a constraining envelope or complete annulus to retain the liquid nucleus pulposus repair prosthesis in the cavity. These devices may extrude, leak, or protrude through the damaged annulus, resulting in considerable pain.

The pain and disability caused by disc degeneration is a serious economic and social problem. Any effective means of improving these conditions without causing more damage or fusion to the spinal disc would play an important role in the medical and medical arts. There is therefore a real need for an implantable prosthetic spinal disc that allows the disc to recover its size, load bearing capacity and flexibility. In addition, there is a need for a simple prosthetic prosthesis that can restore the height of the spinal disc in a slow manner after implantation. Ideally, disc height should recover in a period of greater than 3 hours but less than 3 months.

The artificial spinal disc disclosed in prior art U.S. patent No.4,309,777 to Patil is a prosthetic prosthesis that uses a metal spring and cup. U.S. patent No.4,714,469 to Kenna describes a spinal implant composed of a rigid solid, a portion of the surface of which includes a porous coating. U.S. patent No.4.349,921 to Kuntz relates to an intervertebral disc repair prosthesis including a pair of hard plugs for replacing a degenerated spinal disc. U.S. patent No.3,867,728 to Stubstad et al relates to a device for replacing the entire spinal disc by laminating vertical, horizontal or axial sheets of an elastic polymer. U.S. patent No.4,911,718 to Lee et al relates to a spinal disc elastomeric spacer consisting of three distinct parts, a nucleus, a ring and end plates, each made of a different material. The disc described by Lee has a special layered structure with 3-24 separate layers of unidirectional reinforcing fibers, the components being arranged in a particular direction. U.S. patent No.3,875,595 to frost relates to an inflatable and collapsible plastic biliary nucleus prosthesis. U.S. Pat. Nos. 4,772,287 and 4,904,260 to Ray et al describe cylindrical prosthetic spinal disc capsules with or without a therapeutic agent. U.S. patent nos. 5,674,295 and 5,824,093 to Ray et al describe a prosthetic nucleus prosthesis in the form of a pillow or capsule with a hydrogel core and a constraining cuff. Bao et al, in U.S. Pat. Nos. 5,047,055 and 5,192,326, disclose artificial nuclei made of hydrogels having a bulk form conforming in shape to the intervertebral disc space or a bead form encased in a porous envelope, respectively. Another variation of a nucleus replacement is described in U.S. Pat. No.5,534,028 to Bao et al, which has a different modulus of elasticity in the anterior and posterior portions.

The intervertebral disc is an anatomically and functionally complex joint, consisting of three parts, each with its own unique structural characteristics. It is difficult to design and manufacture such complex prostheses that mimic the function of the natural spinal disc from acceptable materials. The new design disclosed herein provides a solution to this dilemma.

A disadvantage of metal or rigid spinal disc replacements is the inability to provide any shock absorbing resilience or flexibility in multiple planes. The Kuntz device uses a rigid plug to replace the disc space. The multiple components required in the previous Stubstad et al and Lee designs are difficult to manufacture and install. The Lee device is too fragile, complex to manufacture as a replacement for the entire spinal disc, and does not restore height to the spinal disc over time.

Froning and Ray et al use balloons filled with a fluid or thixotropic gel, respectively, but do not address these issues. The device contains a fluid that must be completely sealed to prevent leakage. The fluid in these devices may leak or be squeezed out as the spine undergoes normal bending and twisting movements. The Ray device also requires an inelastic shield. The hydrogel lumbar disc nucleus prosthesis used in the Bao et al patent is much weaker than the entire disc. The function of such a nucleus is to prevent herniation and herniation of the nucleus prosthesis by distributing vertical loads over the damaged or repaired natural annulus.

Yet another problem is the potential for the prior art elastomeric devices to become dislodged or extruded from the intervertebral space.

Disclosure of Invention

It is an object of the present invention to provide a novel spinal disc replacement that is flexible, yet strong, capable of mechanical shock absorption and allows flexibility in movement between vertebrae. Such devices may be permanently implanted as a medical spinal disc. The device of the present invention has a compressive modulus of elasticity similar to that of a normal spinal disc in the range of 0.1 to 10 megapascals. This is much softer than the previously used high molecular weight polyethylene plastics, which typically have a compressive modulus of greater than 100 mpa. The modulus of elasticity of the present invention enables cushioning and the required flexibility.

Yet another novelty of the present invention resides. Is made of a solid material that does not leak. While the liquid or soft gel components described in the Bao and Ray patents may leak and extrude.

In general, any elastomer having biomedical applications may be used, provided that the elastomer has a compressive strength of at least 1 MPa, preferably 10 MPa, when subjected to the load of the human spinal vertebrae. The ultimate elongation of the elastomer should preferably be 15% or more and the ultimate tensile or compressive strength should preferably be 100 kPa or more. Hydrophilic polymers are preferred from the standpoint of biocompatibility and controlled swelling.

The invention also includes improvements in anchoring or adhesion to further prevent extrusion of the device. Such fixation may be achieved by modifying the top and bottom surfaces of the device to allow for fiber attachment and increased friction, or the device may have material extensions from the surface or periphery of the device that may be surgically fixed to the vertebral body.

Moreover, such prosthetic prostheses may also expand or enlarge over time to restore the height of the spinal disc in a controlled manner, thus allowing fixation in situ. None of the prior art describes devices having controlled expansion characteristics that passively change the size of their outer dimensions, although Ray's devices can also swell when implanted.

The device mechanically functions as a normal spinal disc, can be attached to the endplates of the vertebral bodies, and can expand to restore the normal height of the intervertebral space. Such prosthetic discs may be surgically inserted into the intervertebral space. It may separate two bone surfaces in the spine or other parts of the body. Such prosthetic prostheses may be used in humans or as veterinary devices.

The shape of the device is a complex three-dimensional structure that provides both anatomical shape and mechanical support. This anatomical shape has an irregular volume to fill the intervertebral disc space. Body coordinates may be described using anatomical directions of up (toward the head), down (toward the foot), lateral (toward the side), medial (toward the midline), posterior (toward the back), anterior (toward the front). From a top view, the device of the present invention is kidney-shaped with the hilum of the kidney facing posteriorly. The radial extent of the device is substantially contained within the dimensions of the spine.

Drawings

FIG. 1 is a perspective view of a prosthetic spinal disc according to the present invention;

FIG. 2 is an anterior view of a spinal disc for repair;

FIG. 3 is a top or plan view of a spinal disc for repair;

FIG. 4 is a perspective view of a preferred prosthetic spinal disc with an extension portion securable to a vertebral body;

FIG. 5 is a perspective view of a preferred prosthetic spinal disc with a fibrous or surface treatment on the top surface;

FIG. 6 is a perspective view of a preferred prosthetic spinal disc;

FIG. 7 is a top view of a spinal level including a denatured spinal disc region;

FIG. 8 is a side view of a human spinal disc space with a prosthetic spinal disc implanted.

Detailed Description

As shown in FIG. 1, the spinal disc body 10 has a peripheral surface 11, a substantially concave upper surface 12, and a substantially convex lower surface 13. The peripheral surface 11 of the disc body 10 corresponds to the annulus fibrosus (annulus) of a natural disc. The superior surface 12 and inferior surface 13 of the disc body 10 correspond to the vertebral endplates (endplates) in a natural disc. The interior of the disc body 10 corresponds to the nucleus pulposus (nucleus) of a natural disc. Fig. 2 shows a generally rectangular spinal disc body 10 when viewed from the front. As shown more clearly with reference to fig. 8, the peripheral edge 14 of the superior surface 12 is substantially flat with the peripheral edge 15 of the inferior surface 13 to provide a good contact interface for the superior and inferior vertebral bodies 16 and 17.

The upper surface 12 and the lower surface 13 are preferably rough with a surface texture having a roughness index along the height of between about 1 nanometer and about 2 millimeters. The peripheral surface 11 is generally smoother than the rough upper and lower surfaces 12 and 13.

As shown in FIG. 3, the spinal disc body 10 is generally kidney-shaped when viewed from above, having an extended oval surface 18 and a recess 19.

Fig. 4 shows the spinal disc body at least partially surrounded by fixation extensions 22, wherein the fixation extensions 22 are for fixation to adjacent vertebral bodies. The fixed extension 22 includes a band portion 23, a number of lower tabs 24, and a number of upper tabs 25. The band portion 23 can be fixed to the oval extension surface 18 of the peripheral surface 11. The lower tab 24 of the fixation extension 22 may be secured to the lower vertebral body 17. The upper tab 25 of the fixation extension 22 may be secured to the superior vertebral body 16.

FIG. 5 illustrates a preferred embodiment spinal disc body 10 wherein the superior and inferior surfaces 12 and 13, respectively, are covered with fibers or surface texturing such as grooves 26 to enable tissue ingrowth from the adjacent superior and inferior vertebral bodies 16 and 17. In a preferred embodiment, the fibers or surface texture are applied in a cross-hatched direction.

FIG. 6 illustrates yet another preferred embodiment spinal disc body 10 wherein the superior and inferior surfaces 12 and 13, respectively, are provided with small holes or undercuts 27 to enable tissue ingrowth from the adjacent superior and inferior vertebral bodies 16 and 17. In a preferred embodiment, the diameter of the small holes or undercuts 27 is varied.

Fig. 7 shows the degenerative spinal disc region and the herniated spinal disc 28 in contact with the spinal nerve 29. The ponytail is indicated at 30. The dural sac is indicated at 31. The ganglion is indicated at 32. The present invention relates to the replacement of a herniated spinal disc 28 with a spinal disc body 10, as shown in FIG. 8.

For example, fig. 8 shows a spinal disc body 10 implanted between a superior vertebral body 16(L4) and an inferior vertebral body 17 (L5). In the radial plane, the anterior portion 20 of the spinal disc 10 preferably has a greater height than the posterior portion 21 of the spinal disc 10. 33 denotes the articular surface of the ilium and 34 denotes the facet joint.

Example 1

Elastomers useful in embodiments of the present invention include silicone rubber, polyurethane, polyvinyl alcohol hydrogel, polyvinyl pyrrolidone, polyhydroxyethyl methacrylate, HYPAN^TMAnd Salubria^TMA biological material. Methods for preparing these polymers and copolymers are well known in the art. The devices described in this example are made from an elastomeric hydrogel material as disclosed in patent nos. 5,981,826 and 6,231,605, the contents of which are incorporated herein by reference, having a mechanical compression modulus of elasticity of about 1.0 mpa, an ultimate elongation of greater than 15%, and a strength limit of about 5 mpa. Such devices are capable of withstanding forces in excess of 1200 newtons.

One preferred hydrogel for use in embodiments of the present invention is high hydrolysis crystalline polyvinyl alcohol (PVA). The polyvinyl alcohol hydrogel can be prepared by any method known in the art using commercially available polyvinyl alcohol powders. Preferably by the methods disclosed in U.S. Pat. Nos. 5,981,826 and 6,231,605, the contents of which are incorporated herein by reference. Typically, 25 to 50% (by weight) of the polyvinyl alcohol powder is mixed with a diluent such as water. The mixture is then heated at a temperature of about 100 degrees celsius (C) until a viscous solution is formed. The solution is then poured or injected into a metal or plastic mold shaped as shown in figure 1. The device is cooled to below-10 degrees celsius, preferably to about-20 degrees celsius. The device is frozen and thawed several times until a solid device having the desired mechanical properties is formed. The device may then be partially or completely dehydrated for implantation. The resulting prosthetic prosthesis has a mechanical modulus of elasticity of 2 MPa and an ultimate tensile and compressive strength of at least 1 MPa, preferably about 10 MPa. The prosthetic prosthesis produced by this method allows for 10 degrees of rotation between the top and bottom surfaces without failure at torques in excess of 1 Newton meter. The device thus fabricated does not rupture when subjected to the same loading conditions as the natural disc. The device is made of a solid elastomer material and is biocompatible as evidenced by the cytotoxicity and hypersensitivity tests specified by the International organization for standardization (ISO 10993-.

Example 2

The prosthetic spinal disc may be made of a variety of elastomers so long as the shape, elasticity, biocompatibility, and strength requirements are met. These implantable medical devices may be, for example, polyurethane, silicone, hydrogel, collagen, hyaluronidase, protein, and other artificial polymers that can be used to achieve the desired range of elastic mechanical properties. Polymers such as silicones and polyurethanes generally have a value of the mechanical modulus of elasticity of less than 100 mpa. Hydrogels and collagen may also be used to make devices with mechanical modulus of elasticity values less than 20 mpa but greater than 1.0 mpa. The ultimate tensile strength of silicones, polyurethanes and certain hydrogels is typically greater than 100 or 200 kilopascals. Such materials typically can withstand torques in excess of 0.01 newton meters without failure.

The body of the prosthesis may also be reinforced with polyethylene, polyglycolic acid, poly-paraphenylene terephthalamide fibers or filaments arranged in a circumferential direction, preferably to form a complete braided mesh ring within the body of the device, or to form a cross-over structure resembling the annulus of natural spinal disc fibers.

The exact dimensions of the prosthetic spinal disc may vary from patient to patient. Typical dimensions for an adult spinal disc are 3 cm short axis, 5 cm long axis and 1.5 cm thick, but these dimensions may vary by 500% without departing from the spirit of the invention.

Example 3

The device may be fabricated with different weight percentages of polyvinyl alcohol (PVA) at various stages of the molding process to produce various different mechanical elastic moduli within the prosthetic spinal disc, and thus the elastic modulus of the device is not constant. Similarly, two elastomers may be mixed to produce varying modulus of elasticity. Another approach is to incorporate fibers or webs into the device, resulting in an anisotropic elastic modulus.

Example 4

A material for a kidney-shaped device that expands to a fixed size after placement in the body. Such prosthetic prostheses are made from polyvinyl alcohol hydrogels as described by Peppas, which can be prepared by a freeze-thaw cycle process. Reference is made to Polymer, Vol.33, pages 3932 and 3936 (1992); authors Shauna r.stauffer and Nikolaos a.peppas. This prosthetic prosthesis exhibits swelling characteristics and can increase 5% to six times (600%) its original size when placed in a saline bath for 24 hours. The expansion pressure measured in the head-to-tail direction of the device is greater than 1 newton. Expansion and enlargement can occur with a wide variety of materials that expand due to hydration or osmotic pressure. This expansion and enlargement can be used to enhance moisture transport in the material. The expansion of the device may also be achieved by mechanical springs embedded in the device. Alternatively, the height of the device may be increased by an internal spring made from one or more metal or plastic sheets capable of exerting an expansion force of greater than 1 newton. It is anticipated that expansion in the height direction of more than 10% would be useful for such devices and is therefore included in the present invention.

Example 5

Additional adhesion to the vertebral body may be obtained by surface modification on the top and bottom surfaces of the prosthetic prosthesis. Surface modifications may include physical scoring or imprinting of the surface, chemical stimuli applied to the surface, biochemical agents that modify the surface, or fibrils extending from the surface to enhance adhesion to the vertebral body or vertebral endplates. These fibers and surface modifications induce fibrosis or osteogenesis in the body and enhance adhesion to the vertebral body.

Fibrosis can be caused by a number of methods including the formation of open pores or rough surfaces, porous structures with undercuts, the addition of osteoconductive or inducer agents, the addition of other polymers such as polyester fabrics or fibers, the addition of other bioactive molecules such as tumor necrosis factor or collagen, the addition of metal solids or networks, the formation of rough surfaces to depths in excess of 5 nanometers (nm). The rough surface may include 2 millimeter (mm) diameter pores with undercuts, similar to a sponge. The surface may also be biochemically modified to enhance moisture transport or physically modified to enhance chemical transport. It is anticipated that there are many ways to alter the surface characteristics of a prosthetic prosthesis to achieve the same goal of promoting cellular ingrowth or attachment of collagen or bone. These and other factors of the same kind have been anticipated by the present invention.

Example 6

Such a device may have additional parts to enable direct fixation in situ. For example, the prosthetic prosthesis may be provided with helical anchor points capable of being secured into a vertebral body, as shown in fig. 4. The tab extensions of such a device may be made of a hydrogel having a modulus of elasticity between 0.2 and 5 megapascals. The fixation attachment portion may extend from the body of the replacement spinal disc. The elastomer may also be surrounded along the periphery of the spinal disc by a material comprising a continuous fiber ring that is connected to the fixation attachment 22.

The mechanical connection is achieved by a fabric or insert between the expansion body and the vertebrae. The connector may be biodegradable or may be permanent. Polyester fibers, screws, glue, fastening plates, and other similar connectors may be used, but are not limited to these.

Example 7

In a preferred embodiment, a sterile, kidney-shaped prosthetic prosthesis is used as a spinal disc prosthetic prosthesis. The body of this prosthesis is made of a hydrogel material with a mechanical compression modulus of between 1.5 mpa and 10 mpa and an ultimate elongation in a certain direction of more than 50%. The swelling characteristic of this material is that the height can be expanded by 50% when placed in a physiological saline solution. The top and bottom surfaces of the prosthetic that contact the vertebrae have exposed polyester fibers that can be embedded in the body and can stimulate a fibrotic response to the long term connection. In addition, open pores with a depth of 2 mm may be formed in the top and bottom surfaces to promote bony attachment, as shown in FIG. 6. These holes have undercuts that allow a secure connection to be made between the device and the fibrous tissue of the vertebral endplates. Sheets of poly (p-phenylene terephthalamide) fabric may be molded into the device near the peripheral surface and the top and bottom surfaces and extend about 1 centimeter beyond the body of the device. This fabric attachment is used to attach the device to the side of the vertebra.

While examples of the present invention have been described, it will be apparent that many modifications and variations can be made thereto without departing from the spirit and scope of the invention.

Claims (45)

1. An implantable prosthesis, substantially shaped like an intervertebral disc, comprising a biocompatible elastomer having a mechanical modulus of elasticity of less than about 100 mpa and an ultimate tensile strength generally exceeding about 100 kpa, said prosthesis being flexible to allow 2 degrees of rotation between its top and bottom surfaces without failure at torques exceeding 0.01 nm.

2. The prosthetic prosthesis of claim 1 wherein the ultimate strength of the device can withstand compressive loads in excess of 1 megapascal.

3. The prosthetic prosthesis of claim 1 wherein the material of the device has a mechanical ultimate strength in excess of 5 mpa.

4. The prosthesis defined in claim 1, wherein said means is formed from a solid elastomeric material.

5. The prosthetic prosthesis of claim 1, wherein the elastomer has a mechanical modulus of elasticity greater than 1.0 megapascals.

6. The prosthetic prosthesis of claim 1 wherein the elastomer has a mechanical modulus of elasticity of less than 20 megapascals.

7. The prosthetic prosthesis of claim 1 wherein the device has a mechanical modulus of elasticity of less than 10 megapascals but greater than 200 kilopascals.

8. The prosthetic prosthesis of claim 1 wherein the mechanical modulus of elasticity of the elastomer is not constant.

9. Prosthesis according to claim 1, characterized in that the delivered size of the prosthesis is expandable at least in one direction by a minimum of 5% after one day immersion in physiological saline.

10. Prosthesis according to claim 1, characterized in that the delivery size of the prosthesis is expandable in vivo at least in one direction by a minimum of 50% without injection of other materials.

11. Prosthesis according to claim 1, characterized in that the delivery size of the prosthesis is expandable at least in one direction by a minimum of 20% and capable of generating a force of more than 1 newton in the craniocaudal direction one day after implantation in the body.

12. Prosthesis according to claim 1, characterized in that the delivery size of the prosthesis can be enlarged by at least 100% by combining a spring and an elastomer part.

13. The prosthetic prosthesis of claim 1 wherein the prosthesis is modified to provide specific surface features.

14. The prosthetic prosthesis of claim 13 wherein the surface features are modified by physical or biochemical means to provide enhanced adhesion to the vertebral body.

15. The prosthetic prosthesis of claim 13 wherein the surface portion comprises a fabric.

16. The prosthesis of claim 13, wherein the surface portion comprises a metallic solid or mesh.

17. The prosthesis of claim 13, wherein the surface portion includes a porous structure with undercuts.

18. The prosthetic prosthesis of claim 13 wherein the surface portion comprises a roughened surface having a depth in excess of 5 nanometers.

19. The prosthetic prosthesis of claim 13 wherein the surface portion comprises a bioactive molecule.

20. The prosthetic prosthesis of claim 1 wherein surface features of the prosthetic prosthesis are modified to promote cellular ingrowth.

21. The prosthetic prosthesis of claim 1 wherein the surface features are biochemically modified to enhance moisture transport.

22. The prosthetic prosthesis of claim 1 wherein the surface features are physically modified to enhance chemical transport.

23. The prosthesis of claim 1, wherein the device is formed of an elastomer having a modulus of elasticity of between 0.2 and 5 megapascals and has tab extensions secured to adjacent vertebral bodies.

24. The prosthetic prosthesis of claim 1 wherein the intervertebral disc is comprised of a material comprising a continuous annulus fibrosis.

25. The prosthesis of claim 1, further comprising an attachment portion that allows for physical fixation to a vertebral body and prevents displacement of the component in situ.

26. The prosthesis of claim 1, wherein the material is a hydrogel.

27. The prosthetic prosthesis of claim 1 wherein the material is a composite material comprised of more than one substance.

28. The prosthesis of claim 1 being a permanently implantable medical device.

29. The sterile prosthetic prosthesis of claim 1, wherein said body is formed in an ovoid or kidney shape usable as a spinal disc prosthetic prosthesis, enlarged by 20% in height when placed in a physiological saline solution, has exposed fibers on upper and lower surfaces of said body, is comprised of a biocompatible elastomer having a compression modulus between 1.5 mpa and 10 mpa, an ultimate compressive strength in excess of 1 mpa, and an ultimate elongation in a direction greater than 25%, and includes fabric extending from the body for securing to the sides of said vertebrae.

30. The prosthetic prosthesis of claim 1 for use as a medical implant for a spinal disc.

31. Surgically inserting a prosthetic prosthesis according to claim 1 into the intervertebral space.

32. The prosthesis of claim 1 for spacing two bone surfaces.

33. The prosthetic prosthesis of claim 1 for veterinary use.

34. An implantable spinal disc body having an upper surface and a lower surface connected by a peripheral surface, the implantable spinal disc body comprising a biocompatible elastomer having a mechanical modulus of elasticity of less than about 100 megapascals and an ultimate tensile strength in excess of about 100 kilopascals.

35. The implantable spinal disc body of claim 34 wherein the upper and lower surfaces of the implantable spinal disc are kidney-shaped with an extended oval surface and a recessed surface, and the implantable spinal disc is generally rectangular in cross-section.

36. The implantable spinal disc body of claim 34, wherein the peripheral edges of the upper and lower surfaces are substantially flat.

37. The implantable spinal disc body of claim 34, wherein the roughness index of the upper and lower surfaces along the height is between about 1 nanometer and about 2 millimeters.

38. The implantable spinal disc body of claim 37 wherein the peripheral surface has a roughness index of less than 1 millimeter.

39. The implantable spinal disc body of claim 34, wherein the implantable spinal disc body is at least partially surrounded by a fixation extension having a plurality of superior and inferior tabs connected to the band portion for securing the implantable spinal disc to adjacent superior and inferior vertebral surfaces, respectively.

40. The implantable spinal disc body of claim 34 wherein the upper and lower surfaces are covered by a surface texture to facilitate connection with adjacent vertebral bodies.

41. The implantable spinal disc body of claim 34 wherein the upper and lower surfaces are provided with a plurality of small holes to promote tissue ingrowth.

42. The implantable spinal disc body of claim 34, wherein the implantable spinal disc body has a greater thickness in the anterior portion than in the posterior portion.

43. An implantable spinal disc body of biocompatible elastomeric material having a mechanical modulus of elasticity of less than about 100 mpa and an ultimate tensile strength in excess of about 100 kpa, comprising:

a substantially concave upper surface, the peripheral surface of which is substantially flat;

a substantially convex lower surface, the periphery of which is substantially flat;

the upper and lower surfaces are connected by a peripheral surface; and is

The implantable spinal disc body is further characterized as having a kidney shape with an extended oval surface and a recess that is generally rectangular in cross-section and has a front portion that is thicker than a rear portion.

44. The implantable spinal disc body of claim 43 wherein the roughness index of the upper and lower surfaces along the height is between about 1 nanometer and about 2 millimeters and the roughness index of the peripheral surface is less than 1 millimeter.

45. The implantable spinal disc body of claim 43, further comprising:

a band portion of the fixation extension at least partially surrounding a peripheral surface of the implantable spinal disc body; and

a plurality of upper and lower tabs extending from the band portion of the fixation extension for securing the implantable spinal disc body to adjacent upper and lower vertebral surfaces, respectively.