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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 with worse outcomes. METHODS: Data were 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 Activity Score were assessed at 1, 5 and 10 years. Kaplan-Meier survivorship was calculated and compared between BMI groups. RESULTS: All groups had significant improvement in OKS and Tegner scores. BMI 35 + kg/m2 experienced the greatest overall increase in mean OKS of 17.3 points (p = 0.02). There was no significant difference in ten-year survival, which was, from lowest BMI group to highest 92%, 95%, 94% and 93%. CONCLUSION: There was no difference in implant survival between groups, and although there was no consistent trend in postoperative OKS, the BMI 35+ group benefited the most from UKA. Therefore, when UKA is used for appropriate indications, high BMI should not be considered to be a contraindication. Furthermore rationing based on BMI seems unjustified, particularly when the commonest threshold (BMI 35) is used. LEVEL OF EVIDENCE: III.

Original publication




Journal article


Knee surg sports traumatol arthrosc

Publication Date





2259 - 2265


Body mass index, Implant survival, Patient-reported outcome, Unicompartmental knee arthroplasty, Adult, Aged, Aged, 80 and over, Arthroplasty, Replacement, Knee, Body Mass Index, Cohort Studies, Contraindications, Contraindications, Procedure, Female, Humans, Knee, Knee Joint, Knee Prosthesis, Lysholm Knee Score, Male, Middle Aged, Obesity, Osteoarthritis, Knee, Patient Reported Outcome Measures, Postoperative Period, Prospective Studies, Treatment Outcome