Define Osteoporosis. Describe its clinical features, investigations, management and complications.

Definition

Osteoporosis is a systemic skeletal disorder characterised by low bone mass and micro-architectural deterioration of bone tissue, leading to increased bone fragility and a consequent rise in fracture risk. Crucially, the bone that is present is normally mineralised — there is simply too little of it — which distinguishes osteoporosis from osteomalacia (where mineralisation is defective). It is defined operationally by a bone mineral density (BMD) T-score ≤ −2.5.

Classification & Risk Factors

Primary osteoporosis is the commonest: type I (post-menopausal) from oestrogen deficiency (predominantly trabecular bone loss, vertebral and wrist fractures) and type II (senile) of old age (cortical and trabecular loss, hip fractures). Secondary osteoporosis results from an identifiable cause. Risk factors include advancing age, female sex, early menopause, low body weight, smoking, excess alcohol, physical inactivity, family history and prolonged corticosteroid use.

Clinical Features

Osteoporosis is asymptomatic until a fracture occurs — it is a ‘silent disease’. The characteristic presentations are fragility (low-trauma) fractures: of the vertebrae (progressive height loss, thoracic kyphosis ‘dowager’s hump’, and back pain), the hip (neck of femur), and the distal radius (Colles’ fracture). A fragility fracture is one occurring after a fall from standing height or less.

Investigations

Dual-energy X-ray absorptiometry (DEXA) measures BMD at the hip and lumbar spine and is the gold standard: a T-score ≤ −2.5 defines osteoporosis, −1 to −2.5 osteopenia. Fracture-risk tools such as FRAX combine clinical risk factors with BMD to estimate 10-year fracture probability. Radiographs show osteopenia and fractures but are insensitive to early loss. Blood tests (calcium, phosphate, alkaline phosphatase, renal, thyroid, vitamin D, and others) are typically normal in primary osteoporosis and are used to exclude secondary causes and osteomalacia.

Management

Lifestyle/general: adequate dietary calcium and vitamin D, weight-bearing and resistance exercise, smoking cessation, reduced alcohol, and falls prevention. Pharmacological: bisphosphonates (alendronate, zoledronate) are first-line anti-resorptives; alternatives/additions include denosumab (rank-ligand inhibitor), teriparatide (an anabolic PTH analogue for severe disease), and selective oestrogen-receptor modulators/HRT in selected patients. Any secondary cause is treated, and steroid-induced osteoporosis is prevented with bone protection.

Complications

The complications of osteoporosis are those of its fractures: hip fractures carry a high one-year mortality and frequently rob elderly patients of their independence; vertebral fractures cause chronic back pain, progressive kyphosis, height loss and reduced respiratory capacity; and each fracture markedly increases the risk of the next. Complications of treatment include the gastrointestinal effects of oral bisphosphonates and, rarely, atypical femoral fractures and osteonecrosis of the jaw with prolonged anti-resorptive use.

Quantity of bone is reduced but its quality of mineralisation is normal.

• Low bone mass with normal mineralisation → fragility; T-score ≤ −2.5 defines it.
• Primary: post-menopausal (type I, vertebra/wrist) & senile (type II, hip); many secondary causes.
• Silent until a fragility fracture (vertebra, hip, distal radius).
• DEXA is the gold standard; FRAX estimates risk; biochemistry is normal in primary disease.
• Calcium/vitamin D + exercise + falls prevention; bisphosphonates first-line (denosumab, teriparatide).