Medial Unicompartmental Versus Total Knee Arthroplasty in the Treatment of Isolated Anteromedial Knee Osteoarthritis: Two-Year Results from a Double-Blinded, Multicenter, Randomized Trial of 350 Patients

BACKGROUND: The superiority of medial unicompartmental knee arthroplasty (mUKA) versus total knee arthroplasty (TKA) for isolated anteromedial knee osteoarthritis (AMOA) remains a subject of ongoing debate. We present the 2-year results of a multicenter, randomized trial comparing the patient-reported and clinical outcomes of these 2 implant types in the treatment of AMOA.

METHODS: This double-blinded superiority trial recruited patients with severe AMOA at 10 arthroplasty centers and randomized them to undergo either mUKA or TKA. The primary outcome was the average improvement in the Oxford Knee Score (OKS) over 2 years, analyzed by intention-to-treat. A range of patient-reported outcomes served as secondary outcomes. Death, revision, and other reoperations were analyzed as serious adverse events (SAEs).

RESULTS: Between September 2017 and March 2021, 350 patients were randomized: 177 (79 female, 98 male; mean age, 67.7 ± 7.5 years) to mUKA and 173 (84 female, 89 male; mean age, 66.7 ± 7.8 years) to TKA. The average 2-year OKS improvement differed by 3.5 points (95% CI, 2.3 to 4.7; p < 0.001) in favor of mUKA, although this difference was below the generally accepted minimal clinically important difference (MCID) of 4 to 5 points. Ten of the 12 secondary outcomes favored mUKA, while the remaining 2 were nonsignificant. The differences in the Forgotten Joint Score (FJS) (14.1; 95% CI, 9.5 to 18.6), range of motion during the first 2 years (7.0°; 95% CI, 5.3° to 8.7°) and at 2 years (5.5°; 95% CI, 3.6° to 7.4°), Knee injury and Osteoarthritis Outcome Score (KOOS) symptoms score (10.3; 95% CI, 7.8 to 12.8), and Short Form-36 (SF-36) bodily pain score (7.6; 95% CI, 4.1 to 11.1) all favored mUKA and reached the MCID. Non-revision reoperations were performed in 4 patients (2.3%) after mUKA and in 12 patients (6.9%) after TKA (9 of the 12 underwent manipulation under anesthesia); the difference was 4.7% (95% CI, 0.2% to 9.8%). There were no differences in the rates of revision or death between the groups.

CONCLUSIONS: Averaged over the 2-year follow-up, mUKA demonstrated minor advantages that did not achieve clear clinical superiority on the basis of the OKS difference. However, the FJS, range of motion, KOOS symptoms score, and SF-36 bodily pain score all demonstrated differences in favor of mUKA that were clinically meaningful. The overall findings suggest that mUKA and TKA yield similarly favorable short-term results, with small advantages for mUKA.

LEVEL OF EVIDENCE: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.