Patellar instability after total knee arthroplasty.

Twenty-five knees with symptomatic lateral patellar instability after total knee arthroplasty (TKA) were treated by operative realignment. Causes of instability include errors in surgical technique, quadriceps imbalance, and trauma. Fourteen knees had proximal realignment, nine had combined proximal and distal realignment, and two had component revision. At an average follow-up period of 50 months, 20 knees had normal patellar tracking and five had recurrent instability. Two patellar tendon ruptures occurred after combined realignment. Proximal realignment alone, in the absence of component malposition, is recommended for the management of patellar instability. Component malposition should be corrected by component revision. Combined proximal and distal realignment procedures are recommended only with great caution because of the predisposition to serious complications such as patellar tendon rupture.