Bone mineral measurements and the pathogenesis of osteoporosis

Low bone mass (osteopenia) is a major factor in the development of osteoporotic fractures in women after the menopause. The pathogenesis of postmenopausal osteoporosis has been pursued by dual lines of investigation: (1) development of a model to describe involutional bone loss, (2) identification of those factors which result in some healthy women having a greater risk for osteoporosis than others. Bone mineral measurements have been made using in vivo neutron activation analysis and whole body counting for the measurement of total body calcium (TBCa), single photon absorptiometry for the measurement of bone mineral content of the distal radius and dual photon absorptiometry for measurement of the bone density of the spine. TBCa is higher in men than women and is lost at a slow linear rate in men. Blacks have a skeletal mass about 8-9% higher than Caucasians. Women have a similar loss of TBCa to men prior to menopause, but then have an accelerated rate of loss after menopause. The change in bone density of the radius and spine with increasing age is also best described by a 2 phase regression in women, with appreciable loss after age 50