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.