Patellofemoral complications following total knee arthroplasty.

Patellofemoral complications following TKA are largely avoided with proper surgical technique. A variety of surgical exposures, including the midvastus and subvastus approach, has resulted in good clinical success. It is critical to maintain the integrity of the extensor mechanism. The surgeon should be prepared to use specific surgical techniques to assist in exposing the stiff knee and to avoid injury to the patellar tendon. These techniques may include the quadriceps snip, modified V-Y quadriceps turndown, and tibial tubercle osteotomy. When tibial tubercle osteotomy is necessary, the technique of Whiteside, using wire fixation of the osteotomy, is preferred. Selection of the proper femoral component size is important. In general, the surgeon should avoid selecting an excessively large femoral component and overstuffing the patellofemoral compartment. Similarly, the surgeon should restore the patella-implant composite to the original patellar thickness or slightly less when possible. Femoral component positioning is critical to proper patellofemoral tracking. The femoral component rotation should be aligned with the transepicondylar axis of the femur. The anteroposterior axis of the femur as described by Whiteside and Arima is a useful secondary landmark to ensure proper femoral component placement. A slightly lateral femoral component position is favored when possible to further facilitate proper patellar tracking. Proper rotation of the tibial component is important. A variety of surgical techniques and anatomic landmarks may be used to establish proper tibial component rotation. The surgeon must avoid internal rotation of the tibial component leading to an increased quadriceps angle and lateral maltracking of the patella. The patellar osteotomy may be performed using either a calibrated cutting system or an eyeball technique. The surgeon should avoid an oblique osteotomy placing the patellar component on the lateral facet. A cemented all-polyethylene component placed in a medialized position to improve patellar tacking is preferred. Proper soft-tissue tension may require a lateral retinacular release in a small percentage of cases. The superior lateral genicular artery is preserved when possible with the release. Proper patellofemoral tracking must be obtained at the time of the primary TKA. The diagnosis and treatment of the more frequent complications of the extensor mechanism following TKA have been discussed. Although these complications may be successfully treated, most may be largely avoided with proper surgical technique and prosthetic component design.