Hip axis length in an Italian osteoporotic population

Models proposed so far for the pathogenesis of osteoporosis often do not take into account the factors underlying the different incidences of hip fracture in different populations. To address this issue, we identified 34 female patients with hip fracture (HF) and 16 women with at least four vertebral fractures (VF) in a population-based retrospective study. Each participant had a bone mineral density (BMD) measurement of the lumbar spine and hip using a Hologic QDR-2000 scanner, in single beam mode for the latter site. Hip axis length (HAL) was determined automatically (precision 1.5%). HAL derived from 149 normal subjects (age range 19-75 years) was 10.3 +/- 0.5 cm. BMD values found at the femoral neck were almost similar, but differed significantly at the spine between the two groups. Mean values of femur HAL in HF patients (10.55 +/- 0.5 cm) were significantly higher compared with VF patients (9.85 +/- 0.54 cm; p < 0.001). Interestingly, both mean values differed significantly from the mean for normal subjects. Our results demonstrate that patients with multiple vertebral fractures have significantly lower vertebral BMD values but similar femoral neck values compared with patients who fracture at the hip; furthermore, hip axis length was more than 1 SD higher in these latter patients compared with that of VF patients. These results suggest that the size and shape of the hip can explain part of the observed aetiologic differences between these two types of osteoporotic fractures.