Impact of postoperative BMI change on patient-reported outcomes following total knee arthroplasty: A retrospective cohort study.

Abstract

The aim of this study was to investigate whether postoperative weight loss after total knee arthroplasty (TKA) is associated with improved clinical outcomes. We hypothesized that patients who experienced postoperative weight loss would demonstrate greater improvements in patient-reported outcomes than those who maintained or gained weight. A total of 312 patients (383 knees) who underwent primary TKA for osteoarthritis between July 2017 and July 2024 were retrospectively reviewed. Percent change in body mass index from preoperative to final follow-up was calculated, and patients were categorized into three groups: weight-loss (≥5% decrease), weight-maintained (±5%), and weight-gain (≥5% increase). The preoperative and final follow-up data included the Forgotten Joint Score-12 (FJS-12), Knee Society Score (KSS; symptoms and satisfaction), and Knee Injury and Osteoarthritis Outcome Score (KOOS; Pain, Symptoms, ADL, Sports, and QOL). The Patient Acceptable Symptom State (PASS) was determined according to established thresholds for each domain. To account for bilateral cases, linear mixed-effects models were used for continuous outcomes and generalized linear mixed-effects models with a binomial distribution were applied for PASS achievement. Postoperative weight loss ≥5% was observed in 25.2% knees, whereas 15.1% showed weight gain. The weight-gain group showed significantly smaller improvements in ΔKOOS Pain (adjusted mean difference: -7.7 points, p = 0.0006), ΔFJS-12, ΔKOOS ADL, ΔKOOS Sports, and ΔKOOS QOL than the weight-loss group, and the weight-maintained group showed smaller improvement in ΔKOOS ADL. PASS achievement rates did not differ significantly among the three groups. Postoperative weight loss after TKA was associated with greater improvements in pain and several functional outcomes, whereas postoperative weight gain attenuated these benefits. However, the percentage of patients who achieved PASS did not differ among the groups. These findings indicate an association between postoperative weight change and the magnitude of PROMs improvement after TKA.