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Medium-Term Results of Oxford Phase-3 Medial Unicompartmental Knee Arthroplasty

Purpose. To review medium-term results of 49 consecutive patients who underwent Oxford phase-3 medial unicompartmental knee arthroplasty by a single surgeon. Methods. Records of 28 women (mean age, 71 years) and 21 men (mean age, 68 years) who underwent minimally invasive Oxford phase-3 medial unicompartmental knee arthroplasty by a single surgeon were retrospectively reviewed. The Oxford knee score and visual analogue scale (VAS) scores for pain and satisfaction were assessed at the latest follow-up by an independent observer, as were postoperative radiographs for implant position, osteoarthritic changes in the non-replaced compartments, and radiolucent lines of >2 mm or implant subsidence. The survival rate was calculated using Kaplan-Meier survival analysis. Patient demographics, postoperative alignment (varus/valgus), Oxford knee scores, and the progression of osteoarthritis in the other compartments were included in a multiple logistic regression (MLR) analysis to identify significant factors affecting the probability of being satisfied (VAS scores for satisfaction of ≤2). Results. The mean follow-up duration was 7.2 years. No patient was lost to follow-up. Two patients with no knee symptoms died (unrelated to surgery) before the 5-year follow-up. The cumulative survival rate at the 9-year follow-up was 91.2% (95% confidence interval, 87.6–94.5%). There were 4 early failures (before 4 years). One patient early in the series developed avascular necrosis of the lateral femoral condyle with an over-corrected tibiofemoral valgus of 12° at 8 months; the other 3 complained of anterior knee pain, without signs of osteoarthritis. All 4 patients underwent revision with total knee arthroplasty. There were 43 patients with more than 5 years of follow-up and without revision of the prosthesis. Patients who were not satisfied (n=6) were more likely to be <65 years old (n=4, adjusted odds ratio [OR], 3.1; MLR p=0.002) and male (n=4; adjusted OR, 2.3; MLR p=0.02). Six of the 43 patients had lucent lines on radiographs, all of which were partial and under the tibial component. Progression of the arthritis in the patellofemoral and/or lateral compartments was worse in 5 patients. Conclusion. Careful patient selection and good surgical technique contributed to good outcome. Younger male patients should be counselled regarding the higher chance of limited satisfaction.