The effect of body mass index and preoperative weight loss in people with obesity on postoperative outcomes to 6 months following total hip or knee arthroplasty: a retrospective study

Background Few studies have investigated the association between obesity, preoperative weight loss and postoperative outcomes beyond 30- and 90-days post-arthroplasty. This study investigated whether body mass index (BMI) and preoperative weight loss in people with obesity predict postoperative complications and patient-reported outcomes 6 months following total knee or hip arthroplasty. Methods Two independent, prospectively collected datasets of people undergoing primary total knee or hip arthroplasty for osteoarthritis between January 2013 and June 2018 at two public hospitals were merged. First, the sample was grouped into BMI categories, < 35 kg/m 2 and ≥ 35 kg/m 2 . Subgroup analysis was completed separately for hips and knees. Second, a sample of people with BMI ≥ 30 kg/m 2 was stratified into participants who did or did not lose ≥ 5% of their baseline weight preoperatively. The presence of postoperative complications, Oxford Hip Score, Oxford Knee Score, EuroQol Visual Analogue Scale and patient-rated improvement 6 months post-surgery were compared using unadjusted and adjusted techniques. Results From 3,552 and 9,562 patients identified from the datasets, 1,337 were included in the analysis after merging. After adjustment for covariates, there was no difference in postoperative complication rate to 6 months post-surgery according to BMI category (OR 1.0, 95%CI 0.8–1.4, P = 0.8) or preoperative weight loss (OR 1.1, 95%CI 0.7–1.8, P = 0.7). There was no between-group difference according to BMI or preoperative weight change for any patient-reported outcomes 6 months post-surgery. Conclusion Preoperative BMI or a 5% reduction in preoperative BMI in people with obesity was not associated with postoperative outcomes to 6 months following total knee or hip arthroplasty.