Impact of Preoperative Body Mass Index on Functional Recovery After Total Knee Replacement Surgery

Background: Total knee replacement (TKR) is among the most frequently performed orthopaedic procedures worldwide, yet the influence of preoperative body mass index (BMI) on postoperative functional recovery remains a source of considerable clinical debate. Obese patients constitute a disproportionately large share of the TKR candidate pool, particularly in urban Iraqi tertiary-care settings where metabolic comorbidity burden is high. Objective: To evaluate the association between preoperative BMI category and short-to-medium-term functional recovery, pain relief, and complication rates following primary TKR in a Al-Hilla General Teaching Hospital. Methods: A retrospective cohort study was conducted on 248 patients who underwent primary unilateral TKR at a Al-Hilla General Teaching Hospital, between January 2019 and December 2022. Patients were stratified into four BMI categories: normal weight (18.5–24.9 kg/m²), overweight (25.0–29.9 kg/m²), obese class I (30.0–34.9 kg/m²), and obese class II/III (≥35.0 kg/m²). Primary outcomes were the Knee Society Score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Oxford Knee Score (OKS) at 3, 6, and 12 months postoperatively. Secondary outcomes included operative time, length of hospital stay, 90-day readmission rate, and perioperative complications. Results: Patients with obese class II/III BMI demonstrated significantly lower functional scores across all three instruments at 3 and 6 months compared with normal-weight patients (p < 0.01). At 12 months, the difference in KSS narrowed but remained statistically significant (p = 0.04). Operative time was longer in higher BMI groups (p < 0.001), and perioperative complication rates were significantly elevated in class II/III obesity (27.3% vs 7.1%; p = 0.003). Length of hospital stay and 90-day readmission rates also increased with BMI category. Conclusion: Preoperative BMI independently and significantly impacts functional recovery trajectories after TKR. Structured preoperative weight optimisation programmes and targeted postoperative rehabilitation protocols are recommended for obese candidates in resource-limited settings such as Baghdad. Keywords: total knee replacement; body mass index; functional recovery; obesity; knee arthroplasty; Baghdad; WOMAC; Knee Society Score; perioperative complications; rehabilitation