Cemented medial mobile-bearing Unicompartmental Knee Arthroplasty: Effects of compliance with current indications on functional outcomes and long-term survival rates

Background: Unicompartmental knee arthroplasty (UKA) is a surgical option for patients with medial compartment osteoarthritis (OA). The objective of this study was to describe the functional outcomes and long-term survival rates of cemented medial mobile-bearing UKA according to the compliance with current indications. Methods: Retrospective study of 78 patients with medial unicompartimental knee OA treated with mobile-bearing cemented UKA (Oxford phase-III) between 2002 and 2012, with an average follow-up of 10.4 ± 3.4 years. Preoperative radiographs and clinical records were reviewed to assess the compliance with current indications (isolated medial compartment OA, flexion ≥ 90°, integrity of all ligaments, varus deformity<15°). Patients who met all criteria were classified with appropriate indication. The function was measured using the knee society score (KSS). Results: Nineteen (24.3%) patients did not meet the current indications for UKA. Non-isolated OA of the medial compartment was the most frequent inappropriate indication (16 patients), followed by range of flexion<90° (2 patients) and lack of integrity of the ligaments (1 patient). A significant improvement was found on the KSS after surgery [preoperative KSS: 50.0 (Interquartile range-IQR: (35.0–60.0); postoperative KSS: 70.0 (IQR:60.0–70.0), p < 0.05]. Survival after 15 years of follow-up in cases without and with appropriate indication was 55.8% and 89.7%, respectively. A higher risk of revision surgery was found in cases with inappropriate indication (hazard ratio: 4.87, 95% Confidence Interval: 1.54–15.38, p:0.007). Conclusion: When proper patient selection is carried out, cemented medial mobile-bearing UKA offers good functional outcomes with a survival rate of 89.7% at 15 years of follow-up.