Environmental fatigue testing of silastic finger joint prostheses.

Abstract

AbstractHeat vulcanized silicone elastomer (Silastic‐Dow) has been in clinical use as a prosthetic replacement material for over a decade. When subjected to operating stress in body fluids, as in cardiac poppet‐valves, failure has occurred. Fractures of silastic finger‐joint prosthesis have also been experienced.Chemical and fractographic analyses of such failed finger‐joint prostheses raise the suspiciaon of failure. Severe discoloration of the implant at the point of maximal stress concentration, the presence of significant amounts of triglyceride and cholesterol on the fractured prostheses, and the pattern of fracture markings indicate that fracture was due to a combination of chemical surface deterioration and stress concentration.Study of the method of surgical insertion of these prostheses suggests failure to completely excise the volar plate and other palmar joint structures could create a step off and sufficiently increase the stress in the bending element of the device to cause fracture. In vitro cyclic testing at 37°C in serum failed to cause fracture of these devices after 10 million cycles, but did produce gradual discoloration of the entire prosthesis which began and was most noticeable at the point of bending. Although the prostheses adsorb lipid, which may produce surface deterioration, it is anticipated that properly inserted, the service life of these devices should be more than adequate for full clinical application.