A model for involutional bone loss.

Bone mass of the total skeleton and distal radius were measured by in vivo neutron activation analysis and single photon absorptiometry, respectively, in 403 healthy white women and 151 healthy white men. In addition, the density of L-2 to L-4 (bone mineral content of the spine [BMCs]) was measured by dual photon absorptiometry in 159 of these women and in 56 women with the vertebral crush fracture syndrome. The rate of loss of total body calcium (TBCa) and bone mineral content of the radius (BMCr) was linear in men and was slower than in women. The best fit for TBCa and the bone mineral content of the distal radius and spine as a function of age in women was with a two-phase regression. The TBCa and BMCr could be used as well as BMCs to identify women with crush fractures. The ratios of BMCs/TBCa, BMCs/BMCr, and TBCa/BMCr did not differ among women with crush fractures and age-matched normal individuals. Our data do not support the hypothesis that women with vertebral crush fractures have preferential loss of spinal bone.