11.4 · Bone disorders: Osteoporosis

Osteoporosis

Decrease in mineralized bone mass or bone density, leading to fragile bones and increased risk of fractures

General process of osteoporosis

Old bone is reabsorbed faster than new bone is deposited, so bones become thinner and more porous

Peak bone mass age

Around age 30, after which resorption slowly exceeds formation

Why bone mass declines with age

Osteoblasts become less numerous and less active, and physical activity decreases

Detection of osteoporosis

Can be present for decades and is often not known until a fracture occurs, sometimes spontaneously

Post-menopausal osteoporosis

Bone mass declines fastest in the several years after menopause, linked to estrogen deficiency

Estrogen and bone

Estrogen has overall osteoclast-inhibiting activity, so decreased estrogen results in more bone-resorbing cells

Other causes of estrogen deficiency

Stress, excessive exercise, and low body weight, which can cause osteoporosis in younger women

Why osteoporosis is more common in women

The decline in bone-protecting hormones is more gradual in men, and men begin with denser bones so osteoporotic levels are reached at an older age

Secondary osteoporosis causes

Long-term corticosteroid use, endocrine disorders, and alcoholism

Corticosteroids and bone

Directly inhibit osteoblasts and induce osteoblast apoptosis, reduce intestinal calcium absorption, and increase kidney calcium excretion

Endocrine causes of secondary osteoporosis

Hyperparathyroidism and Cushing's syndrome, both of which stimulate osteoclasts

Alcoholism and bone

Directly inhibits osteoblasts

Clinical manifestations of osteoporosis

Kyphosis and fractures due to thin and sparse trabeculae in spongy bone and porous compact bone

Most common osteoporotic fracture sites

Long bones especially the neck of the femur (broken hip), radius, ribs, and vertebrae