Passive motions at the subtalar joint, talonavicular joint and calcaneocuboid joint were measured in eight ankle specimens, using an ultrasonic motion analysis system. Arthrodeses of the three joints were performed in all feasible combinations and the resulting motion change at the unfused joints was determined. Motion at the subtalar joint was not significantly affected by fusion of the calcaneocuboid joint, reduced to one quarter by fusion of the talonavicular and calcaneocuboid joints (double arthrodesis) and almost completely eliminated with all other fusions. Motion at the talonavicular joint was not significantly affected by calcaneocuboid fusion and reduced to approximately one third with the subtalar and the double arthrodesis. Motion at the calcaneocuboid joint was not significantly reduced by subtalar fusion but almost completely eliminated in all fusions involving the talonavicular joint. It is concluded that the talonavicular joint is the key articulation for hindfoot motion. Double arthrodesis preserved significant motion at the subtalar joint. Fusion of the calcaneocuboid joint had no significant influence on remaining hindfoot motion.

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Silastic small joint spacers for the metacarpoflex, and a thermoplastic elastomer, Santoprene, with phalangeal joint fail catastrophically at a reported rate rangthose of Silastic. The materials were evaluated after sterilizaing from 2 to 26%. Although the exact cause of this problem tion by either ethylene oxide or gamma irradiation in an is not known, it is speculated that failure is due to the propa-ASTM standard flexing machine under conditions of high gation of flaws generated in the material surface. In addition humidity and body temperature both before and after artifito wear secondary to bony impingement, these flaws can be cially aging. In each case, the materials investigated preintroduced through manufacturing, surgical handling, and sented significantly lower crack-growth rates than Silastic in vivo frictional wear. In an effort to identify an elastomeric (p Ͻ 0.001). © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, material that will function similarly to Silastic as a self-37, 94-99, 1997. hinging joint spacer but provide an increased functional life, we have investigated and compared the crack-growth

In this article, a protocol for the evaluation of new materials for small joint prostheses is introduced. The testing methods employed in the protocol were developed by reviewing reported clinical failure modes and conditions found in vivo. The methods developed quantitatively evaluates the fatigue, fatigue crack propagation, and wear resistance properties of materials. For this study, a silicone elastomer similar to Dow Corning Silastic HP100, a radiation stable polypropylene, and a copolymer of polypropylene and ethylene propylene-diene monomer (EPDM) are evaluated. None of the materials tested demonstrated the ideal properties that are sought in a self-hinging joint prostheses. The silicone elastomer had excellent wear properties; however, cracks quickly propagated, causing catastrophic failure when fatigued. Conversely, the copolymer showed excellent fatigue crack propagation resistance and less than favorable wear properties. The polypropylene did not perform well in any evaluation.