The Coventry Award. The effects of shelf life on clinical outcome for gamma sterilized polyethylene tibial components.

Tibial component shelf life was examined as a contributory factor of the in vivo failure of gamma sterilized prosthetic knee replacements. One hundred eighty-eight Synatomic total knee replacements sterilized by gamma irradiation in air were implanted by one surgeon into 147 patients between May 1985 and December 1994. Of these, 135 knees in 105 patients with a mean followup of 5.8 years (range, 2.1-11.3 years) were included in the study. The mean shelf life of the implants was 3.6 years (range, 0.1-10.7 years). Clinical failure for this study was defined as component retrieval resulting from polyethylene degradation. The knee components were divided into three different groups determined by their shelf storage durations of 0 to 4 years (Group 1, 93 components), between 4 and 8 years (Group 2, 21 components), or greater than 8 to 11 years (Group 3, 21 components). Six prostheses were revised because of polyethylene degradation after a mean implantation time of 2.5 years (range, 1.1-3.8 years). The mean shelf life of these six prostheses was 8.4 years (range, 5.8-9.6 years). Five years after implantation, prostheses that had shelf lives of less than 4 years had a 100% survival rate. Those that had shelf lives of 4 to 8 years before implantation had an 88.6% survival rate, and those prostheses that had shelf lives greater than 8 to 11 years had a 79.2% survival rate.