Differences in proximal femur geometry distinguish vertebral from femoral neck fractures in osteoporotic women

Bone mineral density (BMD) is generally used to predict the risk of fracture in osteoporotic subjects. However, femoral neck BMD and spine BMD have been reported not to be significantly different among patients with hip or vertebral fractures, suggesting that other risk factors are needed to determine the different fracture types. Proximal femur geometry (PFG) parameters, such as hip axis length (HAL), femoral neck-shaft angle (NSA) and femoral neck diameter (FND) have also been shown to predict the risk of hip fracture. These parameters are statistically different in spine fractures compared with both types of hip fractures (trochanteric and femoral neck) when considered together. We wanted to assess the difference in these parameters by comparing spine fractures with a homogeneous group of hip fractures, i.e. femoral neck fractures. 807 postmenopausal women were divided into three groups; those with vertebral fractures (182), those with femoral neck fractures (134) and a control group without fractures (491). Dual X-ray absorptiometry (DXA) scans of the spine and hip were carried out to measure BMD and define the PFG parameters of the hip. Data were statistically analysed. In agreement with other authors, we found that women with femoral neck fractures had longer HAL, wider FND and larger NSA than controls, whereas there were no statistically significant differences in PFG between women with spine fractures and controls. Logistic regression showed HAL and NSA could predict the risk of femoral neck but not vertebral fracture. These data indicate specificity of some PFG parameters for hip fracture risk.