Association between body mass index change and outcome in the first year after total knee arthroplasty.

There is an association between obesity, osteoarthritis and total knee arthroplasty (TKA), but little is known about how postoperative weight change influences outcomes. Primary TKA patients were identified from an institutional arthroplasty registry. BMI and patient reported outcome measures (PROMs, specifically WOMAC and SF36) were recorded for 1545 patients preoperatively and up to 3 years postoperatively. Mixed effects modelling showed postoperative BMI change had no impact on postoperative WOMAC scores. However, weight gain over 10% had a negative impact on SF36 pain and functional scores although postoperative weight loss was not associated with improved PROMs. Men showed greater improvement in postoperative SF36 function and pain scores, whilst older patients were slower to improve. Postoperative weight gain has a negative association with SF36 pain and function.