Silicone rubber carpal implants: A study of the incidence of late osseous complications

This clinical review of 53 silicone rubber carpal implants done by the senior author (P. R. C.) between 1976 and 1983 determines the incidence of so-called “silicone rubber synovitis.” Although previously reported in small series, the true incidence of this complication of wear of the implant has not been documented. In this study late radiographic follow-up demonstrated lytic lesions adjacent to the carpal implants in 75% of the scaphoid implants, 55% of the lunate implants, and 75% of the scapholunate implants. In patients with x-ray film evidence of lytic lesions, more than half (56%) complained of pain, and more than one fourth (27%) have already had revision surgery. In every patient who had reoperation in this study, the histologic examination of the tissue in the wrist showed a chronic granulomatous process identical to that previously reported in cases of so-called “silicone rubber synovitis.” These “lytic lesions” must be differentiated from “degenerative cysts” that are a part of the natural progression of degenerative arthritis. Four cases were submitted for mass spectrophotometric analysis, and the positive identification of the silica atom was made in all four. This study shows that the wear of carpal bone implants of silicone rubber and subsequent “silicone rubber synovitis” are common occurrences and not rare as has been previously inferred from isolated case report studies. This study suggests that (1) implantation of these implants in young, healthy individuals is rarely indicated, and (2) careful follow-up of patients who already have these implants in place is important. It should be noted that this series of patients does not include those with flexible finger implants, trapezium implants, or flexible hinged-wrist implants; all of which have much different loading stresses than the three carpal bones reviewed and probably are not associated with this seriously high incidence of complications.