Hip fracture risk assessment using composite indices of femoral neck strength: the Rancho Bernardo study

The objective of this work was to examine the prediction of incident hip fracture risk by composite indices of femoral neck strength, constructed from dual X-ray absorptiometry (DXA) scans of the hip. These indices integrate femoral neck size and body size with bone density, and reflect the structure's ability to withstand axial compressive forces and bending forces, and the ability to absorb energy in an impact. We studied a prospective cohort of community-dwelling women, 55 years or older at baseline, average age 72 years, that was established in 1988, with follow-up until 1998. Higher baseline values of each composite strength index were associated with lower risk of incident hip fracture in this cohort. After adjusting for age and body mass index, relative risks associated with each standard deviation increment in the composite indices were 0.39 for compression strength (95% confidence interval 0.25-0.60), 0.43 for bending strength (95% confidence interval 0.27-0.70), and 0.34 for impact strength (95% confidence interval 0.20-0.58). Larger bone size relative to body size was associated with lower risk of incident hip fracture. After adjusting for age, body mass index, and bone density, each standard deviation increment in femoral neck width normalized by body weight was associated with incident hip fracture relative risk of 0.38 (95% confidence interval 0.20-0.70). Our results suggest that composite indices of femoral neck strength, constructed from DXA measurements, have the potential to improve hip fracture risk assessment. This needs further exploration in larger cohorts and in different population sub-groups.