Association between preoperative extracellular water–to–total body water ratio and time to walking independence after total hip arthroplasty: a retrospective cohort study

PURPOSE: To investigate the association between preoperative extracellular water-to-total body water ratio (ECW/TBW) and time to walking independence among female patients undergoing total hip arthroplasty (THA). METHODS: This retrospective cohort study included female patients who underwent primary THA between January and December 2022. Preoperative ECW/TBW was measured using bioelectrical impedance analysis and dichotomized at 0.400. The primary outcome was time to walking independence within 14 postoperative days. Cox proportional hazards models assessed the association between ECW/TBW and walking independence, adjusting for age, comorbidities, nutritional status, skeletal muscle mass index, non-operated knee extensor strength, walking pain, and maximum walking speed. Model performance was evaluated using likelihood ratio tests, Harrell's C-index, and time-dependent area under the curve (AUC). RESULTS: Among 142 patients, 118 (83.1%) achieved walking independence within 14 days. Patients with ECW/TBW ≥ 0.400 achieved walking independence later than those with ECW/TBW < 0.400 (log-rank p < 0.001). In multivariable analysis, ECW/TBW ≥ 0.400 was associated with delayed walking independence (hazard ratio 0.29, 95% CI 0.16-0.52). Including ECW/TBW improved model fit and increased the time-dependent AUC at postoperative day 14. CONCLUSION: Higher preoperative ECW/TBW is associated with delayed walking independence after THA and may complement preoperative assessment when predicting early postoperative functional recovery.