Fracture/dissociation of the polyethylene in metal-backed patellar components in total knee arthroplasty.

We encountered a complication that is unique to the use of a metal-backed patellar component in total knee replacement--namely, fracture and separation of the polyethylene bearing from its metal counterpart. The cases of seventeen patients who were treated at several institutions were studied. Patellar malalignment, especially in heavy patients who had a high level of activity, was a contributory cause of the complication, but we thought that deficiencies in the design of the prosthesis were also an important factor.