Evaluation of Compressive Strength Index of the Femoral Neck in Caucasians and Chinese

Compressive strength index (CSI) of the femoral neck is a parameter that integrates the information of bone mineral density (BMD), femoral neck width (FNW), and body weight. CSI is considered to have the potential to improve the performance of assessment for hip fracture risk. However, studies on CSI have been rare. In particular, few studies have evaluated the performance of CSI, in comparison with BMD, FNW, and bending geometry, for assessment of hip fracture risk. We studied two large populations, including 1683 unrelated U.S. Caucasians and 2758 unrelated Chinese adults. For all the study subjects, CSI, femoral neck BMD (FN_BMD), FNW, and bending geometry (section modulus [Z]) of the samples were obtained from dual-energy X-ray absorptiometry scans. We investigated the age-related trends of these bone phenotypes and potential sex and ethnic differences. We further evaluated the performance of these four phenotypes for assessment of hip fracture risk by logistic regression models. Chinese had significantly lower FN_BMD, FNW, and Z, but higher CSI than sex-matched Caucasians. Logistic regression analysis showed that higher CSI was significantly associated with lower risk of hip fracture, and the significance remained after adjusting for covariates of age, sex, and height. Each standard deviation (SD) increment in CSI was associated with odds ratios of 0.765 (95% confidence interval, 0.634, 0.992) and 0.724 (95% confidence interval, 0.569, 0.921) for hip fracture risk in Caucasians and Chinese, respectively. The higher CSI in Chinese may partially help explain the lower incidence of hip fractures in this population compared to Caucasians. Further studies in larger cohorts and/or longitudinal observations are necessary to confirm our findings.