Foam prosthesis for spinal disc

Abstract

Disclosed herein are spinal disc implants comprising a foam adapted to completely or partially replace a nucleus pulposus within a spinal disc cavity, the foam being a nonabsorbable, closed cell and having a Poisson ratio of less than 0.5. Also disclosed are methods of implanting a foam, either as an in-situ curable material or as a preformed foam.

Description

RELATED APPLICATIONS[0001]This application claims the benefit of priority under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60 / 931,407, filed May 22, 2007, U.S. Provisional Application No. 60 / 930,064, filed May 14, 2007, and U.S. Provisional Application No. 60 / 930,104, filed May 14, 2007, the disclosures of which are incorporated herein by reference.FIELD OF THE INVENTION[0002]Disclosed herein are prostheses for replacing all or part of a nucleus pulposus in a spinal disc area.BACKGROUND OF THE INVENTION[0003]This disclosure relates to treatments and implant materials for treating the medical condition called degenerative disc disease (DDD) by augmenting the intervertebral disc space, with or without the removal of intradiscal tissue, the nucleus pulposus (NP), and localizing, supplementing, or replacing native NP with an in situ curing polymer (Nucleus Replacement Prosthetic or NRP) while the outer intervertebral membrane called the annulus fibrosus (AF) heals after ruptu...

AI Technical Summary

Benefits of technology

The solution effectively reduces re-operation risks by maintaining disc height, preventing implant migration, and allowing for revision without surgical intervention, thus ensuring long-term functionality of the intervertebral disc.

Problems solved by technology

Since such materials are typical of materials generally used in disc replacement, it is likely that studies that report reduced or equal stiffness in a prosthetic-implanted disc have either damaged one of the energy storage mechanisms of the disc or have left a compressible void in the nuclear space.

Our analysis indicates that, in contrast to reports in the literature, a nucleus replacement device having with E>0 (solid) is not ideal for a healthy, normal annulus.

If Eεz and Pa are left uncoupled, these equations have solutions that place unsafe stress on the endplates of the vertebral bodies.

The following details the disadvantage of partially, rather than completely filling the nuclear space.

Fairly large load failures are generated by relatively modest implant modulus.

Despite the fact that a disc with a large defect (4.9 mm) will have a high V, this consequence does not appreciably improve the load failure threshold.

The nuclear material is in an unknown state and likely highly fractured and disordered.

Disc degeneration results in irritating and often painful degradation products, which must be removed.

This will result in an eventual loss of 50% disc height, causing the bony structures of the spine to close around nerves and cause pain.

An aneurysm of the disc is a bulge that impinges on nerves, causing pain.

Because this represents a weak portion of the annulus, merely filling the nucleus to a higher height will not draw the aneurysm in because once the load is re-established the weak portion will bulge to the same extent, since the nuclear pressure under load is not significantly improved.

This is a consequence of the shortness of the disc height, where further shortening may cause pain and a normal 20% deflection is a relatively small distance.

Decreasing the prosthetic modulus below the Endplate Limit risks pain-inducing deflections under load, especially since the procedure involves creating a defect in the annulus.