In osteoporosis, a metabolic bone disorder, the rate of bone resorption accelerates while the rate of bone formation slows down, causing a loss of bone mass. Bones affected by this disease lose calcium and phosphate salts and thus become porous, brittle, and abnormally vulnerable to fracture.
Osteoporosis may be primary or secondary to an underlying disease. Primary osteoporosis is commonly called senile or postmenopausal osteoporosis because it’s most common in elderly, postmenopausal women. (See Osteoporosis in men.)
The cause of primary osteoporosis is unknown; however, a mild but prolonged negative calcium balance, resulting from an inadequate dietary intake of calcium, may be an important contributing factor—as may declining gonadal adrenal function, faulty protein metabolism due to estrogen deficiency, and a sedentary lifestyle.
Causes of secondary osteoporosis include prolonged therapy with steroids or heparin, total immobilization or disuse of a bone (as with hemiplegia, for example), alcoholism, malnutrition, malabsorption, scurvy, lactose intolerance, hyperthyroidism, osteogenesis imperfecta, and Sudeck’s atrophy (localized to hands and feet, with recurring attacks).
Signs and symptoms
Osteoporosis is usually discovered when an elderly person bends to lift something, hears a snapping sound, and then feels a sudden pain in the lower back. Vertebral collapse, producing a backache with pain that radiates around the trunk, is the most common presenting feature. Any movement or jarring aggravates the backache.
In another common pattern, osteoporosis can develop insidiously, with increasing deformity, kyphosis, loss of height, and a markedly aged appearance. As vertebral bodies weaken, spontaneous wedge fractures, pathologic fractures of the neck and femur, Colles’ fractures after a minor fall, and hip fractures are all common.