Influence of age and sex on vertebral shape indices assessed by radiographic morphometry

Vertebral shape indices (VSI) assessed by radiographic morphometry are currently used to define vertebral fractures in clinical trials and epidemiologic studies on osteoporosis. However, there is little information concerning the influence of sex or age on VSI. Furthermore, previous reports on the variation of VSI with age showed conflicting results. The aim of this study was to assess the influence of sex and age on VSI in order to better define reference values for the clinical and epidemiologic evaluation of vertebral osteoporotic fractures. Measurements were performed on thoracic and lumbar spine radiographs from 50 men and 50 women (age range 25-75 years) without evidence of osteoporotic, degenerative or other disease-related vertebral deformity. The anterior (AH), middle (MH) and posterior (PH) heights of each vertebral body from T4 to L5 were measured and VSI were calculated as follows: wedging = (AH minus PH) divided by PH; concavity = (MH minus PH) divided by PH. Wedging and concavity, especially at the mid and lower thoracic spine, increased significantly with age in both sexes. We also demonstrated that VSI at the lumbar spine were significantly dependent on gender, with greater values of wedging and concavity in men than in women. Consequently, reference values used for the definition of vertebral osteoporotic fractures assessed by radiographic morphometry should take into account both sex and age effects.