Obesity Predicts Longer Operative Time and Worse Functional Recovery After Total Knee Arthroplasty Under Enhanced Recovery Protocols in Asian Patients

Background Obesity is a growing global health concern that poses challenges to optimizing outcomes following total knee arthroplasty (TKA). While Enhanced Recovery After Surgery (ERAS) protocols aim to improve perioperative recovery, it remains unclear whether they sufficiently mitigate the adverse impact of obesity, particularly in Asian populations with differing body composition and recovery patterns. Methods A retrospective cohort study was conducted at a tertiary academic center involving patients who underwent primary TKA under a standardized ERAS protocol between January 2020 and December 2021. Patients were stratified into three body mass index (BMI) categories: non-obese (<30 kg/m²), obese class I (30-34.9 kg/m²), and obese class II+ (≥35 kg/m²). Functional outcomes at six months, including Knee Society Knee Score (KSKS), Knee Society Functional Score (KSFS), Oxford Knee Score (OKS), range of motion (ROM), and patient-reported measures, were analyzed across BMI groups. Multivariable linear regression was used to adjust for age, gender, American Society of Anesthesiologists (ASA) classification, and Charlson Comorbidity Index (CCI). Results A total of 334 patients were included (non-obese: n = 245; obese class I: n = 65; obese class II+: n = 24). Patients with BMI ≥35 had significantly lower six-month OKS (β = -3.89, p = 0.013), KSFS (β = -6.68, p = 0.001), and reduced ROM in extension (β = -9.95°, p = 0.005) compared to the non-obese group. Obese class I patients had significantly lower KSFS (β = -2.30, p = 0.004), though OKS and ROM extension were not statistically different. No significant differences were found in surgical complication rates, infection, readmission, or revision. Surgical duration trended longer with increasing BMI but did not reach statistical significance. Conclusion Obesity, particularly BMI ≥35, is an independent predictor of inferior functional outcomes and reduced knee extension following TKA, even within a standardized ERAS pathway. These findings underscore the need for targeted preoperative optimization and rehabilitation strategies for obese patients undergoing TKA.