Unicompartmental mobile-bearing knee arthroplasty.

Two diferent mobile-bearing unicompartmental knee replacement designs have been available since the late 1970s. The primary difference between these two designs is that one has a constrained bearing in a track and the other has a freely moving bearing. Both implants are currently indicated for the treatment of patients with medial unicompartmental osteoarthritis and are available for use in the United States. The benefits of such designs are restoration of normal knee joint kinematics and protection of the polyethylene by reduction of high-contact stresses that occur with nonmobile-bearing designs. Experience has shown that careful patient selection and careful surgical technique both are factors critical to the success of mobile-bearing unicompartmental knee implants. The most important patient selection criteria have proved to be the diagnosis of anteromedial osteoarthritis with a passively correctable varus deformity and intact anterior cruciate ligament. Precise instrumentation is necessary to consistently balance and align a mobile-bearing implant. Ten-year survivorship data for freely mobile-bearing implants are available from multiple centers that show survivorship rates ranging from 85% to 98%, which are comparable to survivorship rates for total knee replacement.