Patellar complications after knee arthroplasty. A prospective study of 56 cases using the Kinematic prosthesis.

A prospective study on 56 knees was performed to analyze the incidence and cause of patellar complications following total knee arthroplasty with the Kinematic prosthesis inserted with the Universal Instrumentation system. Patellar complications occurred in 23 cases: 15 had anterior knee pain. There was 1 case of patellar fracture. Subluxation of the patella occurred in 13 cases, of which 6 were painful. Although the mechanical alignment was correctly reconstructed to neutral in all but 2 cases, the instrumentation tended to allow malpositioning of the components into excessive femoral valgus and compensatory excessive tibial varus that predisposed to patellar subluxation. With this prosthesis and instrumentation, patellar stability is hindered by a very short anterior femoral flange, a shallow patellar groove, and insertion of the components at 3 degrees to the mechanical axis. It should be ensured that the components are correctly positioned, that patellar stability is carefully checked before closing the capsule, and that lateral release is performed more often.