The influence of sterilization method on wear performance of the low contact stress total knee system

Sterilization method changes to the Low Contact Stress (LCS) Total Knee System (DePuy Orthopaedics Inc, Warsaw, Ind) have resulted in progressive improvements in wear resistance. Initially, the system used the traditional gamma in air irradiation sterilization method, but was transitioned to Gas plasma sterilization. The Gas plasma technique did not introduce free radicals that subsequently oxidize with extended shelf aging found with gamma in air irradiation. This oxidation has demonstrated a significant reduction in mechanical properties leading to increased wear. The introduction of Gas plasma was also accompanied by a transition to polyethylene resins that no longer contained calcium stearate, surmised to influence the rate of oxidation. More recently, gamma irradiation and storage of the polyethylene components in an essentially oxygen-free environment imparted by gamma irradiation in a vacuum foil pouch (GVF), has been shown to protect the implant from oxidation. Additionally, the GVF process imparts the beneficial effects of moderate crosslinking that has been demonstrated to improve wear resistance.