Obesity should not be considered a contraindication to medial Oxford UKA: long-term patient-reported outcomes and implant survival in 1000 knees

Purpose Some health providers ration knee arthroplasty on the basis of body mass index (BMI). There is no long-term data on the outcome of medial mobile-bearing unicompartmental knee arthroplasty (UKA) in different BMI groups. This study aimed to determine the effect of patient body mass index (BMI) on patient reported outcomes and long term survival of medial UKA in a large non-registry cohort. Our hypothesis is that increasing BMI would be associated worse outcomes. Methods Data was analysed from a prospective cohort of 1000 consecutive medial mobile-bearing Oxford UKA with mean 10 year follow-up. Patients were grouped: BMI<25, BMI 25 to <30, BMI 30 to <35 and BMI 35+. Oxford Knee Score (OKS) and Tegner scores were assessed at one, five and ten years. Kaplan-Meier survivorship was calculated and compared between BMI groups. Results All groups had significant improvement in OKS and Tegner scores, with a 4.6 point OKS difference in means at 10 years (p=0.001). BMI 35+ kg/m2 experienced the greatest overall increase in mean OKS of 17.3 points (p=0.02). Ten-year survival from lowest BMI group to highest was 91.5%, 94.5%, 93.8% and 92.6% (n.s.). Conclusion There was no consistent trend in post-operative OKS, with the BMI 35+ group benefiting the most from UKA, and no difference in implant survival. Rationing may be unjustified when UKA is used for appropriate indications.