Effect of medial-lateral malpositioning of the femoral component in total knee arthroplasty on anterior knee pain at greater than 8 years of follow-up.

BACKGROUND: The trochlea is often medialized after total knee arthroplasty (TKA) resulting in abnormal patellar tracking, which may lead to anterior knee pain. However, due to the difference in shape of the natural trochlea and the patellar groove of the femoral component, a medialization of the femoral component of 5 mm results in an equal patellar position at 0-30° of flexion. We tested the hypothesis that more medialization of the trochlea results in a higher VAS pain score and lower Kujala anterior knee pain score at midterm follow-up.

METHODS: During surgery a special instrument was used to measure the mediolateral position of the natural trochlea and the prosthetic groove in 61 patients between 2004 and 2005. Patient reported outcome measures were used to investigate the clinical results (NRS-pain, NRS-satisfaction, KOOS-PS and Kujala knee score).

RESULTS: In total 40 patients were included. The mean follow-up was 8.8 years. A medialization of ≥5 mm resulted in a significantly lower NRS-pain (0.2 vs. 1.4; p=0.004) and higher NRS-satisfaction (9.6 vs. 8.2; p=0.045). Overall clinical results were good; KOOS-PS was 33.9 and Kujala knee score was 72.1.

CONCLUSIONS: The present study showed that a more medial position may result in a better postoperative outcome, which can probably be explained by the non-physiological lateral orientation of the trochlear groove in TKA designs.

LEVEL OF EVIDENCE: Level III.