Is lower extremity joint replacement surgery associated with weight loss? An institutional retrospective study of 36,993 cases.

Total joint arthroplasty (TJA), including total hip (THA) and knee arthroplasty (TKA), improves mobility and quality of life. While often assumed to promote weight loss, evidence on long-term weight change remains mixed. In this large retrospective cohort study of 36,993 adults undergoing primary TJA at a tertiary academic center (2016-2021), we characterize weight and BMI changes following TJA, and identify postoperative weight patterns across preoperative BMI subgroups. BMI and weight were recorded at surgery and at routine 3-month postoperative intervals. Patients were stratified by baseline BMI to assess weight trajectories across subgroups (<25, 25 to <30, 30 to <35, 35 to <40, ≥40 kg/m²). Both THA and TKA patients demonstrated modest short-term BMI reductions within 1-3 months (-0.55% and -1.15%, respectively). However, by 13-15 months, net BMI change approached baseline for THA (-0.09%) and TKA (-0.65%). Patients with BMI ≥ 40 kg/m² exhibited the greatest initial loss (-1.30%) but later rebounded above baseline (+0.21%). Across all BMI groups, absolute changes in BMI and body weight were minimal, with an inflection toward weight regain at 7-9 months. Thus, TJA does not necessarily drive clinically meaningful or lasting weight loss, underscoring the importance of integrated perioperative weight-management strategies, particularly for patients with obesity.