Waist-To-Hip Ratio Is More Predictive of Patients-Reported Outcomes After Total Joint Arthroplasty Than Body Mass Index: A Prospective Cohort Study.

OBJECTIVES: Obesity has an important impact on the future of total joint arthroplasty (TKA). We aimed to determine whether waist-to-hip ratio (WHR) is a useful measurement in predicting postoperative outcomes associated with obesity in patients undergoing primary TKA and compared the predictive value of WHR to that of body mass index (BMI). METHODS: Prospective data from patients undergoing unilateral primary TKA from February to May 2024 were analyzed, including BMI and WHR. Outcomes included complications, hospitalization details, and 12-month patient-reported function (University of California, Los Angeles [UCLA] activity scale, the Hospital for Special Surgery [HSS] score). Multivariable regression models were used to identify significant obesity-related predictors of outcomes. RESULTS: A total of 195 patients were included, with the mean BMI of 28.2 ± 5.2 kg/m2 (range: 17.6-40.8) and the mean WHR of 1.03 ± 0.08 (range: 0.83-1.27). WHR was a significant predictor of wound complication (OR: 1.087, p = 0.016). Both WHR (OR: 1.153, p = 0.004) and BMI (OR: 1.058, p = 0.021) independently predicted systemic complications, with WHR explaining greater variance ( R 2  = 0.241 vs. 0.107 for BMI). For functional outcomes, higher WHR was associated with poorer UCLA activity scores (RR: 0.877, p = 0.012) and HSS function scores (RR: 0.921, p < 0.001), whereas BMI only showed significance for HSS function scores (RR: 0.960, p = 0.002). WHR again explained more variance in HSS function scores ( R 2  = 0.233 vs. 0.124). In contrast, neither WHR nor BMI correlated with surgical records, hospitalization days, or HSS pain scores (all p > 0.05). CONCLUSIONS: The WHR demonstrates superior predictive value over BMI for perioperative complications and 12-month patient-reported functional outcomes following primary TKA. Preoperative WHR assessment may help surgeons improve risk stratification and better educate obese patients regarding postoperative expectations prior to elective TKA.