A new value of proximal femur geometry to evaluate hip fracture risk: true moment arm.

This study was undertaken to determine the influence of proximal femur geometry on hip fracture risk independent of bone mineral density. We examined 34 hip fracture subjects (17 men, 17 women) and 36 control subjects (18 men, 18 women). The control subjects were matched with the hip fracture patients by femoral neck bone mineral density (+ or - 0.100 g/cm(2)). Hip axis length (HAL), femoral axis length (FAL), femoral neck-shaft angle (Theta angle), lateral and medial femoral cortical thickness were measured on standart pelvic radiographs. In the literature, there are conflicting views of the relationship between femur geometry and hip fracture risk which may be explained by different definitions of some parameters. We investigated the effect of a new parameter called true moment arm (TMA) on hip fracture risk. Longer TMA may be correlated to higher transmission of impact energy to the femoral neck. Thus it may be useful to define fracture prone individuals. The results of this study showed that HAL, FAL and TMA were significantly longer in the hip fracture subjects compared to the control group (p<0.001). Hip fracture patients had thinner lateral and medial femoral cortical thickness (p<0.001). Theta angle was wider in the hip fracture group than in the control group (p<0.001). In conclusion, our study showed that evaluation of TMA in addition to HAL, FAL, Theta angle, MCT and LCT can be used to determine of the fracture risk independently of BMD.