Relationship between Trunk Muscle Fat Infiltration and Aspiration Pneumonia after Hip Fracture in Older Women: An Exploratory Study

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Objectives: This exploratory study investigated the association between trunk muscle quality assessed at admission, including muscle fat infiltration, and the development of aspiration pneumonia within 12 months after hip fracture in older women. Methods: This retrospective, single-center study included women aged ≥75 years with hip fracture who underwent abdominal computed tomography at admission. Trunk muscle quality, including muscle fat infiltration and the proportions of normal-attenuation and low-attenuation muscle, was assessed. Participants were classified according to the occurrence of aspiration pneumonia within 12 months after hip fracture, and trunk muscle characteristics were compared between groups. Results: Women who developed aspiration pneumonia showed a significantly higher intramuscular adipose tissue/total attenuation muscle area index in the erector spinae at admission. In multivariable logistic regression analysis, reduced muscle quality of the erector spinae was associated with the subsequent development of aspiration pneumonia (odds ratio, 1.29; 95% confidence interval, 1.05–1.60). Conclusions: Fat infiltration in the erector spinae muscle may be associated with the subsequent development of aspiration pneumonia in older women with hip fracture. Trunk muscle quality at admission may reflect underlying vulnerability. However, these findings should be interpreted with caution given the exploratory design, small sample size, and potential residual confounding; no causal relationship can be established.