MATERIALS AND DESIGN CONCEPTS FOR AN INTERVERTEBRAL DISC SPACER .1. FIBER-REINFORCED COMPOSITE DESIGN

The intervertebral disc is a complex joint anatomically and functional ly. it may be displaced or damaged due to trauma or a disease process. To alleviate this condition, it may be necessary to remove the involv ed disc surgically and fuse the two adjacent vertebrae. Fusion is one option; however, replacing the damaged disc (or part thereof) with a s uitable synthetic equivalent to allow near normal joint motion is more desirable. Unfortunately, the complex mechanical properties of the lu mbar disc cannot be duplicated with homogeneous synthetic materials (p olymers). To overcome this fundamental problem we have developed ratio nal designs utilizing biocompatible thermoplastic elastomers of variou s stiffnesses (durometers) with and without fiber reinforcements. Our design consisted of three components analogous to the natural end plat es, annulus, and nucleus. In this study only the fiber-reinforced desi gn is considered. The variables examined in the present study included orientation of the fiber layers, number of fiber layers, and order of the reinforcing layers. The results of mechanical testing of the fibe r reinforced disc spacer indicate that a range of compressive and tors ional properties can be achieved. The results further demonstrate that properly developed, this design results in properties similar to the natural disc. Designs developed provided adequate compression and comp ression torsion properties for a synthetic spine disc spacer. (C) 1994 John Wiley & Sons, Inc.