Clinical Significance and Pathogenesis of Osteoporosis

Abstract

SummaryThe development of osteoporosis with advancing age in man is a widespread if not a universal phenomenon. The average loss between youth and old age amounts to about 15% of the skeleton but involves a much larger proportion of trabecula than of cortical bone.The princpal clinical manifestation of osteoporosis is fracnure, and three osteoporotic fracture syndromes can be defined: the lower forearm fracture, which predominantly affects women between the ages of 50 and 65; the fracture of the proximal femur, which affects both sexes over the age of 70; and the relatively rare vertebral crush fracture syndrome, which may present at any age but is most common in elderly women.The lower forearm fracture rate is inversely related to the mean normal lower forearm x-ray "density" of the wrist, which falls by about 30% in the 15 years following the menopause. This process, which is associated with corresponding trabecular bone loss elsewhere in the skeleton, is associated with a corresponding rise in the fasting urinary calcium excretion. Some degree of negative calcium balane, and consequent bone resorption, probably occurs in everyone during the later part of the night because calcium absorption is completed within about three to five hours of a meal. In postmenopausal women, however, the sensitivity of the bone to parathyroid hormone appears to be increased, and their nocturnal negative calcum balance therefore comes to exceed the positive balance which can be achieved during the waking hours.Femoral neck fractures in old people reflect the further progression of osteoporosis with advancing age since the fracture rate is inversely correlated with the mean thickness of the metacarpal cortex in the normal population. This progressive osteoporosis is associated with and could well result from a steady decline in calcium absorption which is at least partially attributable to vitamin-D deficiency and reversible on vitamin-D treatment.

Parathyroid Function in Primary Osteoporosis

“…Because of morphometric (1,2) and biochemical evidence (3) that bone resorption is increased in primary osteoporosis and because it is believed that bone resorption is primarily regulated by parathyroid hormone (PTH),1 PTH may play a causal or permissive role in the pathogenesis of osteoporosis (4)(5)(6)(7). However, parathyroid function has not been assessed directly in this disorder.…”

Differential changes in bone mineral density of the appendicular and axial skeleton with aging: relationship to spinal osteoporosis.

“…In recent years, several methods of quantifying BMC of the appendicular skeleton have been developed (4). These measurements, however, have not provided good discrimination between subjects with spinal osteoporosis and age-and sex-matched controls (5)(6)(7). Because appendicular bone is predominantly cortical, whereas the vertebrae are predominantly trabecular, Nordin (6), and Mazess (4), and we (7) have hypothesized that subjects with spinal osteoporosis have lost disproportionately large amounts of trabecular bone.…”

Biochemical Parameters of Vitamin D Nutriture in Old People in Jerusalem

“…Osteomalacia has apparently not disappeared, particularly from northern Europe, and it may play a role in the deterioration in bone status which is often accepted as a characteristic of the aging process (19). It has also been suggested (1) that osteomalacia in the elderly contributes much to the steep rise in incidence of femoral-neck fractures with advancing age.…”