The effect of patellar button placement and femoral component design on patellar tracking in total knee arthroplasty.

The effects of patellar button position and femoral component design on patellar tracking were investigated roentgenographically and arthroscopically using fresh-frozen adult anatomic specimen knees. Patellar tracking was evaluated for medial/lateral position and tilting angle deviation by comparing preoperative normal values to total knee replacement performance with the following variables: (1) femoral component design; symmetrical total condylar type with a 3-mm central patellar groove and a component with a 3-mm raised lateral patellar flange and 1-mm deepened patellar groove; and (2) patellar button placement; central insertion; and 10-mm medialized insertion. In the roentgenographic study, medialized position of the patellar button allowed the bony portion of the patella to assume its normal lateral position and tilt throughout the knee range of motion. A combination of medialized position of the patellar button and deepening of the patellar groove provided the most anatomically correct position and the most normal tilting of the bony structure of the patella. In the arthroscopic study, the centralized patellar position caused significant lateral tracking and subluxation relative to the femoral component, whereas the medialized position eliminated this tracking disorder. Deepening the patellar groove minimized the intraarticular tracking abnormality and constrained the patellar button in the patellar groove. These results show that the position of the patellar button and femoral component design exert a major influence on patellar tracking.