Sex differences in age-related loss of vertebral trabecular bone mass and structure--biomechanical consequences.

Density, structure, and biomechanical competence of trabecular bone were analyzed on cylinders from the central part of the third lumbar vertebral body (L3) from 91 normal individuals aged 15-91 years (48 males and 43 females). A significant and identical age-related decrease (p less than 0.001) in bone density (apparent ash-density and trabecular bone volume) was found for both males and females. The structural analyses revealed a marked, age-related increase (p less than 0.001) in the distance between the horizontal trabeculae in both sexes. In individuals older than 75 years, this increase was significantly higher for females than for males (p less than 0.05). No other significant sex-related differences could be demonstrated in the age-related changes in the trabecular network. The biomechanical compression tests showed a significant and identical age-related decrease (p less than 0.001) in stress-values in the vertical direction for both males and females. When horizontal cylinders were compressed, a steady decrease of bone strength was seen in males, while in females there was a tendency to a pronounced loss of bone strength around the age of 40-50 years. The present study demonstrated clearly a sex-related difference in the changes in vertebral trabecular architecture with age, with a higher tendency to perforation of the horizontal supporting struts in females than in males. The biomechanical consequences of this in these normal individuals were minor--but might be very marked in osteoporotic patients.