Howmedica sterilization technique called "gamma irradiation in air" used on hip and knee protheses prior to orthopedic surgery may increase risk of osteolysis.

Investigation and potential lawsuit and currently numerous individual actions against Howmedica and other companies in connection with Howmedica's use of a technique known as gamma irradiation in air to sterilize the hip and knee prostheses for orthopedic surgery.

Those hip and knee protheses are made of high molecular weight polyethylene, which is like a pliable plastic. The sterilization process caused the polyethylene part of the devices, once implanted in the body, to break up into small pieces that lodge into the patient's hip or knee joint. In the body's fight to rid itself of those pieces, the immune system also turns on the patient's healthy bone, causing it to decay, a condition known as osteolysis . These patients inevitably need a second surgery to replace the device long before expected. Oxidation, which is a time-dependent byproduct of gamma sterilization in air, has an adverse effect on the material properties and wear resistance of polyethylene. Oxidation occurs when oxygen combines with free radicals in the polyethylene that are generated by radiation. The oxidation can occur during irradiation, or it can occur over time as oxygen diffuses into the polyethylene and combines with residual free radicals.