VERTEBRAL SIZE IN ELDERLY WOMEN WITH OSTEOPOROSIS - MECHANICAL IMPLICATIONS AND RELATIONSHIP TO FRACTURES

Reductions in bone density are a major determinant of vertebral fractu res in the elderly population, However, women have a greater incidence of fractures than men, although their spinal bone densities are compa rable, Recent observations indicate that women have 20-25% smaller ver tebrae than men after accounting for differences in body size, To asse ss whether elderly women with vertebral fractures have smaller vertebr ae than women who do not experience fractures, we reviewed 1,061 compu ted tomography bone density studies and gathered 32-matched pairs of e lderly women, with reduced bone density, whose main difference was abs ence or presence of vertebral fractures, Detailed measurements of the dimensions of unfractured vertebrae and the moment arm of spinal muscu lature from T12 to L4 were calculated from computed tomography images in the 32 pairs of women matched for race, age, height, weight, and bo ne density, The cross-sectional area of unfractured vertebrae was 4.9- 11.5% (10.5+/-1.4 vs 9.7+/-1.5 cm(2); P < 0.0001) smaller and the mome nt arm of spinal musculature was 3.2-7.4% (56.4+/-5.1 vs 53.1+/-4.4 mm ; P < 0.0001) shorter in women with fractures, implying that mechanica l stress within intact vertebral bodies for equivalent loads is 5-17% greater in women with fractures compared to women without fractures, S uch significant variations are very likely to contribute to vertebral fractures in osteoporotic women.