A biomechanical study of the effects of simulated ulnar deviation on silicone finger joint implant failure.

UNLABELLED: Silicone finger arthroplasties are used widely, especially for metacarpophalangeal joint replacement in patients with inflammatory arthritis. Implant failure is well recognized. The rates of failure in vivo differ substantially from experience in vivo. One cause of failure is felt to be post-operative ulnar deviation. The aim of our study was to test the effect of ulnar deviation testing on silicone finger implants. We tested 12 implants in three groups of four implants. The implants were submerged in a bath of Ringer's solution at 370 °C throughout the experiment and tested in a rig held in 0°, 10° and 20° deviation. The rig was cycled at 1.5 Hz from 0°-90°. The implants were inspected every 500,000 cycles until a total of 4 million cycles. There was consistently increased wear and supination plastic deformity in going from 0°-20° deviation. This study confirms the adverse effects of ulnar deviation on silicone finger implant wear. It is likely that this combines with lateral pinch forces and sharp bone edges to cause catastrophic silicone implant failure.

LEVEL OF EVIDENCE: III.