Medial unicompartmental knee arthroplasty after knee osteotomy is safe and effective in the absence of excessive valgus overcorrection

Abstract Purpose Limited evidence exists regarding the safety and efficacy of medial unicompartmental knee arthroplasty (UKA) in patients with end‐stage medial arthritis following knee osteotomy. This study aims to evaluate survival, functional and radiological outcomes in patients undergoing medial UKA following knee osteotomy. Methods A retrospective analysis was conducted evaluating 63 knees (60 patients; 62% men, 38% women; mean age 61 ± 8 years; body mass index 28 ± 5 kg/m 2 ) who underwent medial UKA ( n = 47 mobile‐bearing, n = 16 fixed‐bearing) following knee osteotomy. Patients were considered suitable for medial UKA if they met the Oxford criteria and had a preoperative hip–knee–ankle angle (HKAA) < 5° valgus and a medial proximal tibial angle (MPTA) < 95°. Primary outcomes were cumulative revision rates for (1) conversion to total knee arthroplasty (TKA) and (2) any reoperation. Functional outcomes were assessed using the Oxford Knee Score (OKS) and the UCLA Activity Score. HKAA was measured to determine overall limb alignment pre‐ and post‐operatively. Results The average time from osteotomy to UKA was 11 ± 8 years, and the mean follow‐up after UKA was 5 ± 2 years. The cumulative 8‐year implant survival rate was 96.3% (95% confidence interval [CI]: 0.912–1.0) for revision to TKA and 93.2% (95% CI: 0.899–0.965) for any reoperation. Two patients required revision to TKA due to overcorrection and infection. The mean OKS improved from 25.5 ± 5.9 preoperatively to 42.8 ± 6.0 post‐operatively ( p < 0.001). The mean preoperative HKAA of 2.4 ± 3.0° varus was corrected to 0.0 ± 3.1°. Conclusion Medial UKA after knee osteotomy represents a viable treatment option, but it requires a strict preoperative alignment assessment. In the absence of excessive mechanical valgus alignment (HKAA < 3° valgus) and severe valgus deformities (MPTA < 95°) of the proximal tibia, medial UKA provides favourable midterm implant survivorship and excellent functional outcomes. In borderline cases, fixed‐bearing implants should be considered to avoid valgus overcorrection. Level of Evidence Level IV.