L.T. is a 55-year-old man with a 20-year history of rheumatoid arthritis (RA) and body mass index of 28 kg/m2. He has had bilateral knee joint replacements, the most recent performed 2 years ago. L.T. ambulates with two single-point canes to increase mobility and decrease knee pain. Three weeks ago, he was diagnosed with locally invasive prostate cancer. Prior to starting pharmacotherapy for prostate cancer, he received a bone mineral density study that revealed osteoporosis. The oncologist referred L.T. to rehabilitation for development of a conditioning program as part of an osteoporosis management strategy. L.T.’s current pharmacotherapy for RA includes nonsteroidal anti-inflammatory drugs and disease-modifying antirheumatic drugs (Chapter 34) as well as long-term intermittent use of glucocorticoids (Chapter 23) during acute RA flare-ups. The pharmacotherapy for prostate cancer is designed to suppress testosterone production and destroy in situ cancer cells. Suppression of endogenous testosterone production will be accomplished by continuous dosing with goserelin plus flutamide for the first several weeks (Chapter 22). Radiation therapy will be initiated to destroy in situ cancer cells in the prostate. To help prevent further bone loss, L.T. also began taking over-the-counter vitamin D and calcium carbonate and the prescription drug alendronate. These agents are to be continued as long as goserelin is administered.
Physical therapists are well aware that bones provide support for the body and serve as attachment sites for muscles to enable mobility. Every day, therapists evaluate and provide interventions for the most common dysfunctions of the skeletal system—fractures and osteoporosis. While clinicians know that calcium and vitamin D are required for “strong bones,” the dynamic regulation of bone mineral homeostasis is extremely complex with old theories being revised and intricate interplays among hormones and other endogenous substances still being discovered.
Calcium and phosphate are the major mineral constituents of bone and are also two of the most important minerals for general cellular function. Accordingly, the body has evolved a complex set of mechanisms by which calcium and phosphate homeostasis is carefully maintained. Approximately 98% of the 1-2 kg of calcium and 85% of the 1 kg of phosphorus in the human adult are found in bone, the primary reservoir for these minerals. Bone is constantly remodeling, with ready exchange of minerals with free ions in the extracellular fluid. Bones not only serve as the principal structural support for the body, but also provide space within the bone marrow for hematopoiesis. Dysfunction in bone mineral homeostasis can have many clinical consequences. Obviously, disruptions of its rigid structural support can result in osteoporosis and fractures. Abnormalities in bone mineral homeostasis can also result in electrolyte disturbances, with manifestations of muscle weakness, tetany, and coma. Finally, hematopoietic capacity may be reduced in conditions such as infantile osteopetrosis.
The average American diet provides 600-1000 mg of calcium per day, ...