Preoperative CT-Based Pelvic Sarcopenia and Subcutaneous Adiposity Predict Anaemia and Operative Time in Acetabular Fracture Surgery: A Retrospective Cohort Study

Background and Objectives: Acetabular fracture surgery is associated with substantial perioperative blood loss and prolonged operative time. Routine preoperative pelvic computed tomography (CT) carries information about body composition that is not currently exploited for risk stratification. We tested whether (i) CT-defined pelvic sarcopenia is associated with lower preoperative haemoglobin and a greater perioperative haemoglobin drop, and (ii) preoperative subcutaneous fat cross-sectional area (CSA) independently predicts operative time, after adjustment for surgical approach, age, fracture complexity and sarcopenia status. Materials and Methods: In this single-centre retrospective cohort study, 48 adults (37 men, 11 women; mean age 40.2 ± 16.5 years) who underwent open reduction and internal fixation (ORIF) for unilateral acetabular fractures between 2016 and 2024 were included. Pelvic muscle and subcutaneous fat CSAs were measured on the contralateral side of preoperative CT images using ImageJ. Sarcopenia was defined a priori as a sex-specific bottom tertile of psoas CSA. Group comparisons used Welch's t-test or Mann–Whitney U; correlations used Pearson's r; the multivariable model used ordinary least squares regression. A sensitivity power analysis was performed for all primary tests. Results: Sarcopenic patients (n = 17) had significantly lower preoperative haemoglobin (12.63 ± 1.24 vs. 14.00 ± 1.53 g/dL; mean difference −1.37 g/dL, 95% CI −2.20 to −0.55; p = 0.002; Cohen's d = 0.96) and a greater perioperative haemoglobin drop (ΔHb 1.64 ± 0.91 vs. 2.46 ± 1.87 g/dL; p = 0.046; d = 0.52) compared with non-sarcopenic patients (n = 31). Psoas, iliacus, gluteus medius–minimus and total muscle CSAs all correlated positively with preoperative haemoglobin (r = 0.42 to 0.49; all p ≤ 0.003). In the multivariable model (overall F[6, 41] = 3.71, p = 0.005; adjusted R² = 0.26), subcutaneous fat CSA (B = +0.25 min/cm², 95% CI +0.09 to +0.41, p = 0.004) and the modified Stoppa approach (vs. Kocher–Langenbeck; +65 min, p = 0.001) independently predicted operative time, while age, fracture complexity and sarcopenia did not. Conclusions: Routine preoperative pelvic CT in acetabular fracture patients can be repurposed as a one-stop opportunistic screen for two clinically actionable phenotypes: pelvic sarcopenia, which flags lower haematopoietic reserve and a greater perioperative haemoglobin drop, and elevated subcutaneous adiposity, which independently predicts longer operative time. Both findings can be obtained at zero marginal cost or radiation burden and could inform preoperative blood-product preparation, prehabilitation triage, and operating-room scheduling.