A BMI above 30 results in satisfying outcomes in patients undergoing fixed-bearing lateral unicompartmental knee arthroplasty

Purpose: The purpose of this study is to analyse the effect of BMI on clinical outcomes of cemented fixed-bearing lateral unicompartmental knee arthroplasty (UKA) on a 2- to 12-year follow-up. Methods: Between January 2010 and January 2020, a total of 103 lateral UKAs were implanted. The Oxford Knee Score (OKS) and the Western Ontario and McMaster University Osteoarthritis Index for pain, stiffness, function, and total score were administered to estimate patients' overall health status pre- and post-operatively. Results were considered good or excellent for WOMAC values > 85 points and OKS > 40 points. Survivorship, described with Kaplan-Meier method, was defined as the lack of revision at the latest follow-up. Complications or further operations were recorded. p values of < 0.05 were considered significant. Results: One hundred one lateral UKAs were assessed at a mean follow-up of 77.8 months. No patients underwent revision, but 2 patients (2, 0%) developed aseptic loosening of the implant 2 and 5 years after surgery but for clinical reasons neither undergo revision (5-year survivor 97.2%). Overall satisfaction was generally high, with excellent scores in all WOMAC subscales and OKS for all BMI groups. Considering the pain subscale (WOMAC pain), patients with normal weight and overweight achieve excellent results more frequently [10 (25.64%) vs 10 (23.81%) p = 0.026] than obese patients (n = 0); on the other hand, considering the quality of life (WOMAC QoL), obese patients most frequently reach excellent values, even statistically significant [n = 15 (75.00%) p = 0.040]. Conclusion: Although obesity has historically been described as a contraindication to UKA, improved outcomes with modern UKA implant designs have challenged this perception. Therefore, the classic contraindication of UKAs in patients with BMI > 30 kg/m2 may not be justified. According to the present study, lateral UKA patients with BMI > 30 kg/m2 had satisfactory patient-reported outcome measures compared to non-obese patients on a long term with survival rates comparable to medial UKA. Obese patients should not be excluded from the benefit of lateral UKA surgery.