Skeletal Muscle Mass Index and Risk of Lower Extremity Ulcers: Analysis of NHANES Data with External Hospital Validation

ObjectiveTo examine the association between skeletal muscle mass index (SMI) and lower extremity ulcer (LEU) risk, and to develop and externally validate a prediction model incorporating SMI.MethodsWe analyzed NHANES 1999-2004 data and validated findings in a hospital-based cohort. LEUs included diabetic foot, venous, arterial, and pressure ulcers. SMI was calculated from DXA-derived appendicular lean mass. Logistic regression assessed SMI-LEU associations; restricted cubic splines tested non-linearity. LASSO identified predictors for a nomogram, evaluated using AUC, calibration, and decision curve analysis (DCA).ResultsAmong 7194 participants, lower SMI quartiles were associated with higher LEU odds (Q1: OR = 1.74, 95% CI 1.06-2.86; Q2: OR = 1.76, 95% CI 1.03-3.03 vs Q4). No non-linear association was observed. The final model (SMI group, marital status, smoking, diabetes, CKD, RBC) showed acceptable discrimination (AUC: 0.618 training; 0.682 validation) and acceptable calibration, although its clinical applicability remains limited.ConclusionLower SMI showed an independent association with increased LEU risk, and the exploratory model incorporating SMI and clinical factors provides preliminary evidence for its potential use in future risk assessment research.