Sex differences in major postoperative morbidity after elective abdominal surgery: independent of chronological age, frailty, and muscle strength in adjusted analysis

Clinical responses to acute physiological stress differ widely among patients of similar age and comorbidity. Frailty and muscle strength commonly indicate physiological reserve, yet the role of sex remains incompletely understood. This study aimed to assess the unadjusted association between sex and major morbidity and determine whether sex independently is independently associated with major postoperative morbidity. In this prospective multicenter cohort, 223 adults undergoing elective abdominal surgery (2023–2025) had frailty and preoperative handgrip strength assessed. Major postoperative morbidity (Clavien–Dindo grade ≥ III) was analyzed using multivariable logistic regression including chronological age, oncologic indication, frailty status, admission handgrip strength, and sex. Secondary analyses examined length of stay. Major postoperative complications occurred in 6.3% of patients and were more frequent among men than women (10.3% vs. 2.0%, p = 0.032). In multivariable analysis (n = 216 complete cases), female sex was independently associated with lower odds of major complications compared with male sex (OR 0.12, 95% CI 0.02–0.72; p = 0.020). Chronological age (OR 1.02 per year, 95% CI 0.97–1.07; p = 0.533), frailty status (p = 0.557), admission handgrip strength (p = 0.723), and oncologic indication (p = 0.116) were not independently associated with major morbidity. In secondary analyses, oncologic indication (p < 0.001) and frailty status (p = 0.001) were independently associated with prolonged length of stay, whereas chronological age was not (p = 0.972). These findings suggest sex-specific postoperative vulnerability persists beyond age and physiological reserve, supporting inclusion of sex in perioperative risk stratification.