"Restoring Aging Bones".  Rosen, C.L.  Scientific American.  March 2003., pp.55-63.
Osteoporosis affects 10 million Americans, especially post-menopausal women.  Half of all post-menopausal women will incur an osteoporosis-related fracture during their lifetime.  Drugs are available to restore bone loss and reduce the chance of additional fractures.  A new diagnostic tool, dual-energy x-ray absoptiometry (DEXA), measures bone mineral density at sites susceptible to fracture.  Genetics are now known to greatly influence the likelihood of fractures and bone density loss.  Essentially, the entire skeletal system replaces itself every 10 years.  This remodeling is done by osteoblasts and osteoclasts.  Scientists are studying the bone remodeling in hopes of creating drugs that control the loss of bone density.  A new therapy using synthetic estrogen may be on the way, which will help post-menopausal women who no longer produce estrogen naturally.  The parathyroid hormone can be considered the driving force behind osteoporosis, as it promotes the action of osteoclasts.