Environmental fatigue testing of silastic finger joint prostheses

Abstract

SummaryHeat 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 suspicion of fatigue 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 s t e p off and sufficiently increase the stress in the bending element of the device to cause fracture. In vitro cyclic testing a t 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.

An Animal Model for the Implantation of a Bone Liner in the Flexible Implant Arthroplasty

“…The application of this theory to the flexible joint implant was discounted by a 1973 study indicating an insignificant amount of lipid transfer between the joint fluid and the implant. That study also showed no correlation between the small amount of lipid transfer and the frequency of implant fracture (11,12).…”

The role of stress‐enhanced reactivity in failure of orthopaedic implants

“…To test this hypothesis we attempted to duplicate the constraint in our machine, as shown schematically in Fig.7. T h e prosthesis still lasted lo7 cycles without failure (19), but the discoloration at the point of severest bending was now quite intense, almost as much as the prostheses which had failed in use. Since the locations of the discolored regions suggest that mechanical stress aids the absorption of lipids, and the crazed or roughened surfaces could serve as fracture initiators (following the corrosion fatigue analogy), it was decided to remove the prostheses for examination, the results of which we now report below.…”

Oxidation of Silicone Elastomer Finger Joints

“…Weightman et al 4 reported that discoloration of silicone rubber as a result of lipid absorption is accelerated by flexural stresses. The yellowing of the implant hypothetically was attributed to the lipid absorption.…”

“…[1][2][3][4][5][6] The mechanism of degradation of the silicone elastomer material in the finger joints is addressed incompletely in the literature.…”