Osteoporosis

Osteoporosis is a metabolic bone disease characterised by low bone mass and microarchitectural deterioration of bone tissue, leading to increased bone fragility and susceptibility to fracture. It develops silently over years through an imbalance between bone resorption and bone formation and most commonly presents clinically as a fragility fracture of the hip, spine, or wrist.

Definition

Osteoporosis is a systemic skeletal disorder defined by reduced bone mineral density and deterioration of bone microarchitecture, resulting in compromised bone strength and an increased risk of fragility fracture.

Scope

The entry covers osteoporosis as a metabolic and laboratory-relevant entity: the cellular imbalance of bone remodelling that underlies it, the hormonal and nutritional factors that drive bone loss, its measurement by bone densitometry, and its distinction from other metabolic bone diseases. It does not provide pharmacological regimens or individualised management advice.

Key concepts

• Bone remodelling and the resorption-formation balance
• Osteoclasts and osteoblasts
• Bone mineral density and T-score
• Oestrogen deficiency and postmenopausal bone loss
• Peak bone mass
• Fragility fracture
• Secondary osteoporosis

Mechanisms

Bone is continuously remodelled by osteoclasts that resorb it and osteoblasts that form it; osteoporosis results when resorption outpaces formation, so that bone mass declines and trabecular and cortical microarchitecture deteriorate. After the menopause, falling oestrogen accelerates osteoclastic resorption, producing rapid bone loss, while ageing reduces osteoblastic formation; deficiencies of calcium and vitamin D, and conditions or drugs (such as glucocorticoid excess) that disturb bone metabolism, can further drive secondary osteoporosis. The net loss of bone mineral density and the disruption of bone structure reduce bone strength and raise the risk of fracture from low-energy trauma, which is the clinical hallmark of the disease.

Clinical relevance

Osteoporosis is a major cause of fracture and disability in ageing populations and is identified through bone mineral density measurement and the assessment of metabolic and hormonal contributors; biochemical evaluation helps exclude secondary causes. This entry explains how the disease is defined and classified for reference and does not constitute treatment guidance for any individual.

Epidemiology

Osteoporosis is common in older adults and especially in postmenopausal women, and the fragility fractures it causes, particularly of the hip and spine, are an important source of morbidity, loss of independence, and excess mortality. Its prevalence rises with population ageing.

Evidence & guidelines

The pathophysiology and clinical features are summarised in major disease reviews, and the contribution of vitamin D and calcium to bone health is addressed in the wider metabolic-bone literature; these sources are cited for orientation rather than as prescriptive instructions.

History

Osteoporosis was long regarded as an inevitable feature of ageing until the recognition, in the twentieth century, that oestrogen deficiency after the menopause is a major driver of accelerated bone loss. The development of bone densitometry provided an objective measure of bone mass and allowed osteoporosis to be defined quantitatively, transforming it into a measurable and identifiable disease.

Seminal works

• compston-2019
• eastell-2016

Frequently asked questions

What causes the bone loss in osteoporosis?

It results from an imbalance in bone remodelling in which osteoclastic resorption exceeds osteoblastic formation; oestrogen deficiency after the menopause and the changes of ageing are leading contributors, and certain diseases and drugs can cause secondary osteoporosis.

How is osteoporosis identified objectively?

It is identified primarily by measuring bone mineral density, commonly with dual-energy X-ray absorptiometry, with low density and a history of fragility fracture indicating compromised bone strength; laboratory testing helps identify secondary causes.