The sarcopenia index (SI), calculated as the ratio of serum creatinine to cystatin C level, represents skeletal muscle mass and strength. This study aimed to investigate the association between SI and the risk of second hip fractures, considering various demographic and clinical factors to improve second hip fracture risk prediction.

This prospective cohort study included older adults with low-energy hip fractures who were monitored for at least two years to track the incidence of subsequent hip fractures. Baseline demographic, clinical, and biochemical data were collected. The SI was calculated as serum creatinine [mg/dL]/cystatin C [mg/L]) × 100. Logistic regression models were used to evaluate the relationship between the SI and the risk of a second hip fracture. Subgroup analyses were conducted to assess the effects of potential modifiers, including gender, body mass index, hypertension, diabetes, and estimated glomerular filtration rate. Receiver operating characteristic (ROC) curve analysis was conducted to evaluate the predictive performance of SI.

A total of 637 patients were included, 59 of whom experienced a second hip fracture during the follow-up period. The patients with second hip fracture exhibited significantly lower SI levels than those without (48.93 ± 8.54 versus 62.95 ± 14.39, P < 0.001). Logistic regression analysis revealed a significant association between a lower muscle-reduction index and an increased risk of a second hip fracture in the fully adjusted model (odds ratio: 0.91; 95% confidence interval: 0.87–0.94; P < 0.001). The area under the ROC curve for predicting a second hip fracture based on the SI was 0.822, indicating good predictive accuracy. Furthermore, subgroup analyses revealed that SI was inversely associated with second hip fracture.

The SI serves as a significant predictor of second hip fractures in older adults, even after considering age, gender, and clinical factors.