Osteoporosis is a condition where there is a reduction in the density of the bones. Osteopenia refers to a less severe reduction in bone density than osteoporosis. Reduced bone density makes bone less strong and more prone to fractures.

Pathophysiology

Osteoporosis is the result of an imbalance in the normal process of bone remodelling by osteoclasts and osteoblasts. During normal ageing, bone breakdown by osteoclasts increases and is not balanced by new bone formation by osteoblasts, resulting in a combination of:

• Reduced bone mineral density (BMD) and bone mass.
• Changes in bone composition, architecture, size, and geometry.

Bones mass decreases with age but will depend on the 'peak' mass attained in adult life and on the rate of loss in later life.

Bone loss is accelerated in osteoporosis by an imbalance between bone resorption and formation. The age when osteoporosis becomes apparent depends on:

• Peak bone mass - depend on nurition (vitD and calcium), sex hormone levels, levels of physical activity
• Oestrogen deficiency - reduced osteoblast activity
• Glucocorticoids

Risk factors

The main risk factors for osteoporosis can be remembered by the mnemonic SHATTERED FAMILY:

• S – Steroid use
• H – Hyperthyroidism, hyperparathyroidism
• A – Alcohol and smoking
• T – Thin (BMI<22)
• T – Testosterone deficiency
• E – Early menopause