We compared the incidence of wear-related failures between two large cohorts of patients undergoing total knee arthroplasty implanted with identical modular tibial trays and polyethylene inserts sterilized by different methods. A total of 1183 second-generation press-fit condylar prostheses having inserts packaged and sterilized in an oxygen-free environment were assessed at a minimum 5-year followup (mean, 7.0 years). Wear-related failure was defined as (1) osteolysis greater than 100 mm2 or (2) revision of the implant resulting from osteolysis, polyethylene wear, chronic synovitis, and/or effusion. Wear-related survivorship was calculated using Kaplan-Meier survival analysis. Results were compared with our previously published study of 1287 first-generation press-fit condylar modular knees having inserts sterilized by gamma irradiation in air at 5-year minimum followup (mean, 7.8 years). The wear-related failure rate for the second-generation design was 1.1% and 10-year survivorship was 97.0% compared with 8.3% failure and 87.7% 10-year survival for the first-generation design. For second-generation components, patient age was the only variable correlated with wear-related failure. For first-generation components sterilized in air, several variables were correlated to wear-related failure with shelf age of the polyethylene insert being the most important factor. These data emphasize the dramatic effect improvements in polyethylene manufacturing, specifically sterilization methods, can have on implant survivorship.
Level of evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.