The growth and age-related origins of bone fragility in men.

Abstract

At any age, a lower proportion of men than women sustain fractures because fewer men have the structural determinants of bone strength below a critical level where loads exceed bone strength. During aging, bone size increases more in men than in women by means of periosteal apposition, which increases the sex difference in bone size established during growth. Volumetric bone mineral density (BMD) at the spine is similar in young men and women. It decreases less in men, not because trabecular bone loss is less than in women, but rather because periosteal apposition is greater in men than in women. At the hip, volumetric BMD decreases similarly in men and women because greater periosteal apposition in men is matched by greater endosteal bone loss. Volumetric BMD is similarly reduced in elderly men and women. Trabecular architecture is less disrupted and cortical porosity is less in men than in women. Men with fractures have reduced bone size and reduced volumetric BMD owing to growth and age-related factors; both will need to be studied to understand the structural basis of bone fragility in old age.