MATERIALS AND DESIGN CONCEPTS FOR AN INTERVERTEBRAL DISC SPACER .2. MULTIDUROMETER COMPOSITE DESIGN

The main function of the intervertebral disc is to transmit and attenu ate compressive and torsional forces, and stabilize the intervertebral joint, Unfortunately, the disc may be displaced or damaged due to tra uma or disease causing the nucleus to herniate and protrude into the v ertebral canal or intervertebral foramen. Pressure on the spinal nerve may cause pain or paralysis in the area of its distribution. At prese nt, the surgical procedures used to alleviate this condition include d isc excision, and/or spinal fusion, A more desirable situation would i nvolve removing the nucleus pulposus and part or all of the annulus fi brosis and implanting a suitable biofunctional equivalent, Such a pros thesis should attenuate stresses and prevent abnormal stress at adjace nt intervertebral joints, Maintenance of normal disc height would prev ent impingement of the posterior facet joints and facet joint syndrome . In a previous companion paper (J. Applied Biomat. 5:125-132; 1994), the mechanical behavior of disc prostheses manufactured from fiber rei nforced, elastomeric thermoset resins were examined. In order to devel op devices which were more practical from a manufacturing standpoint a nd extremely reproducible, the fiber reinforced thermoset resins were replaced by multi-durometer thermoplastic elastomeric materials, In th e present paper, the mechanical properties of thermoplastic multicompo nent designs have been investigated. (C) 1995 John Wiley and Sons, Inc .