EQUIVALENT STRENGTH AND GAIT AFTER TOTAL KNEE ARTHROPLASTY AND UNICOMPARTMENTAL KNEE ARTHROPLASTY, BUT HIGHER FUNCTIONAL SCORES IN UKA: A PROPENSITY SCORE–MATCHED STUDY HIGHLIGHTING THE ROLE OF RANGE OF MOTION

Abstract

The aim of this study was to compare clinical outcomes, including functional scores, muscle strength, and gait ability, between unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) after adjusting for baseline characteristics. Propensity score matching was performed for 656 TKA and 116 UKA patients with knee osteoarthritis based on age, sex, body mass index, hip–knee–ankle angle, Kellgren–Lawrence grade, Charlson comorbidity index, knee range of motion, and New Knee Society Score (NKSS) functional activity. This yielded 98 matched pairs. NKSS, knee range of motion, knee flexion and extension muscle strength, and the Timed Up & Go (TUG) test were compared with Mann-Whitney U test between groups at two years postoperatively. After matching, patient characteristics were comparable between groups (TKA: 75.3 ± 7.1 years; UKA: 75.0 ± 6.2 years). Preoperative median knee flexion and extension were 130° and −5° in both groups, with no significant differences in NKSS items, muscle strength, or TUG. At discharge, median knee flexion after UKA (125°) was greater than that after TKA (120°)(p = 0.003). At two years postoperatively, median flexion remained significantly higher after UKA (140° vs. 125°, p < 0.001). While NKSS symptoms, satisfaction, and expectations were comparable, median functional activity scores were higher in the UKA group (78 vs. 68, p = 0.04). No significant differences were observed in knee flexion and extension muscle strength or TUG at any time point. In this propensity score–matched comparison, TKA achieved muscle strength, gait function, and patient satisfaction comparable to UKA. The higher functional scores in UKA appear attributable to greater postoperative range of motion rather than differences in strength or recovery.