Time dependent changes in patellar tracking with medial parapatellar and midvastus approaches

The aim of this study was to compare the alteration of patellar tracking by time, which was performed through two different approaches: midvastus and medial parapatellar. Twenty-one patients undergoing simultaneous bilateral primary total knee replacements were randomized prospectively to perform the surgery via a medial parapatellar approach on one knee and midvastus approach on the other knee. All of the patellae were resurfaced. Preoperative, early and late postoperative (mean 22 month) skyline views of the patellae were taken. We found that preoperative 2.24° lateral tilt of patella had not changed by time at the midvastus side (2.95° and 2.57°). Moreover, preoperative 0.48% lateral subluxation of the patella for midvastus approach had not changed (1.48% and 1.67%). Although 2.19° patellar lateral tilt had not significantly changed at the early postoperative period, which was performed via medial parapatellar approach, there had been a significant increase to 5.38° by time (P=0.037) compared to the preoperative radiographs. Additionally, the preoperative lateral subluxation of the patella (0.57%) at the medial parapatellar side had increased to 5.43% at the early (P=0.009) and 5.62% at the late (P=0.012) postoperative measurements. Midvastus approach is superior to medial parapatellar approach concerning the late patellar tracking.