Lateral and patellofemoral compartment osteoarthritis progression after medial unicompartmental knee arthroplasty: A five- to 10-year follow-up study

The purpose of the study was to evaluate lateral and patellofemoral osteoarthritis (OA) progression after medial unicompartmental knee arthroplasty (UKA) and identify factors affecting the progression that were not identified previously.

We evaluated 146 patients who underwent medial UKA between 2009 and 2014. Kellgren–Lawrence grading of lateral and patellofemoral OA was performed on preoperative and final follow-up knee radiographs. Radiographic and clinical characteristics, SF-36, and Oxford knee scores were compared between the OA progressed and non-progressed groups. Risk factors for lateral and patellofemoral OA progression were evaluated.

The lateral OA progressed and non-progressed groups significantly differed in side, preoperative flexion contracture, preoperative joint line convergence angle, postoperative tibiofemoral angle, insert size, revision status ( P < 0.05), and the patellofemoral OA progressed and non-progressed groups significantly differed in age, pre- and postoperative flexion contracture, postoperative tibiofemoral angle and pre- and postoperative patellofemoral OA grade ( P < 0.05). At the final follow-up, Visual Analogue Scale, Oxford Knee Scores, and SF-36 sub-scores were significantly better in the lateral OA non-progressed group ( P < 0.001).

Dominant leg (odds ratio (OR): 2.759), insert size (> 4, OR: 2.219), revision status (+, OR: 6.692), and postoperative tibiofemoral angle (> 5.5°, OR: 1.177) were independent risk factors for lateral OA progression, whereas age (> 60 years, OR: 3.222), preoperative patellofemoral OA grade (> 1, OR: 2.085), and postoperative flexion contracture (> 10°, OR: 1.919) were those for patellofemoral OA progression.

Mild radiographic progression of 1 KL grade is frequently seen five to 10 years after medial UKA. Postoperative outcomes are significantly affected by lateral compartment OA progression but not by patellofemoral OA progression.