This randomized trial enrolled 350 patients with severe isolated anteromedial knee osteoarthritis across 10 arthroplasty centers to compare medial unicompartmental knee arthroplasty (mUKA) with total knee arthroplasty (TKA) over a 24-month follow-up. The primary outcome was average improvement in the Oxford Knee Score (OKS), with secondary outcomes including Forgotten Joint Score (FJS), range of motion, KOOS symptoms, SF-36 bodily pain, and safety events like reoperations, revision, and death.
Main results showed mUKA had a statistically significant advantage over TKA in OKS improvement, with a difference of 3.5 points (95% CI, 2.3 to 4.7; p < 0.001). Other outcomes favored mUKA: FJS difference of 14.1 points (95% CI, 9.5 to 18.6), range of motion during the first 2 years difference of 7.0 degrees (95% CI, 5.3 to 8.7), range of motion at 2 years difference of 5.5 degrees (95% CI, 3.6 to 7.4), and KOOS symptoms difference of 10.3 points (95% CI, 7.8 to 12.8). SF-36 bodily pain score difference was 7.6 points (95% CI, 4.1 to 11.1). Non-revision reoperations occurred in 4 patients (2.3%) after mUKA versus 12 patients (6.9%) after TKA (95% CI, 0.2% to 9.8%), while revision or death showed no differences.
Safety analysis indicated non-revision reoperations, revision, and death were considered serious adverse events, with discontinuations and tolerability not reported. A key limitation is that the OKS difference of 3.5 points was below the generally accepted minimal clinically important difference of 4 to 5 points, which may limit clinical significance. Practice relevance suggests mUKA and TKA yield similarly favorable short-term results, with small advantages for mUKA, but the evidence does not support clear clinical superiority due to the minor OKS difference.
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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.
