Sex differences in age-related changes in vertebral body size, density and biomechanical competence in normal individuals.

Size, ash-density and biomechanical competence were investigated on whole vertebral bodies (L2) from 90 normal individuals (47 males and 43 females), aged 15-91 years. At all ages, cross-sectional area was significantly greater in males than in females. Furthermore, in males a significant increase of 25-30% in cross-sectional area was demonstrated with aging (r = 0.33, p less than 0.05). Conversely, no age-related change in cross-sectional area was detected in females (r = 0.03, n.s.). A significant and identical age-related decrease (p less than 0.001) in apparent ash-density was found for both males and females. Biomechanical compression tests revealed significant and identical decreases (p less than 0.001) in vertebral body load and stress with age in both males and females. However, because of their greater cross-sectional area and an increase in this with age, the level for the load-values was higher in men than in women up to the age of 75 years (p less than 0.05). The present study has demonstrated that in men there is a significantly greater cross-sectional area and a significant increase in vertebral body size, due to continuous periosteal growth. This could, to some extent, compensate for the unavoidable loss of vertebral bone density and stress with age. No age-related compensatory mechanism could be demonstrated in women.