ORPC Introduction

    An introduction to osteoporosis, its causes and the impact it has on society

What is Osteoporosis?

Osteoporosis has been defined as a 'systemic skeletal disorder, characterised by low bone mass and micro-architectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture.'

Osteoporosis is a long-term condition and is the most common bone disorder, occurring mainly in older people, especially postmenopausal women. Some cases are secondary to other diseases (e.g. Cushing's syndrome, coeliac disease) or an adverse medication effect (such as corticosteroid therapy). Women are at a greater risk of osteoporosis than men because of the decrease in oestrogen production after the menopause that accelerates bone loss. However, men are also affected; the lifetime risk of fracture after age 50 in men is just under half that in women. The number of people with osteoporosis will increase as the population ages.

Osteoporosis has been compared to cardiovascular disease and hypertension; it is a long-term condition in which fracture is the acute event, analogous to myocardial infarction and stroke in the other two disease states. Secondary prevention of myocardial infarction has long been established as standard clinical practice. This is not yet the case for patients presenting with fragility fractures that result from osteoporosis and the propensity to fall.

Apart from age, bone mineral density (BMD) is the greatest risk factor for a fragility fracture (the clinically important outcome). Osteoporosis has been defined in terms of BMD score. A 'T-score' of ≥ 2.5 standard deviations (SD) below the young adult mean has been classified as osteoporosis by the World Health Organisation (WHO). Overall fracture risk increases two-fold per unit SD decrease in BMD and this relationship is even greater for hip fractures and BMD measured at hip sites.

However, using BMD alone to assess fracture risk is not ideal as many fragility fractures will occur in patients with a T-score above −2.5 SD. In response to this challenge, the WHO's fracture risk assessment tool (FRAX(r)) has been developed; it takes into account other clinical risk factors that predict fracture risk, independent of age and BMD.

What are the Causes of Osteoporosis?

Osteoporosis occurs when bone remodelling - the balanced process by which bone is renewed and repaired - is disrupted by a variety of factors, some of which can be modified and some of which cannot at present.It is thought that the potential for any individual to develop osteoporosis is determined by both genetic and environmental factors. These in turn determine:

•The peak bone mass achieved at maturity

•The age at which bone loss starts

•The rate of bone loss

A variety of risk factors increase the risk of fracture, and many of these do so by increasing the risk of osteoporosis. Factors influencing the development of osteoporosis are:

Age: Bone density begins to decline in both sexes around the age of 35. In women there is a phase of accelerated bone loss in the 10 years or so following the menopause, while in men there is a steady decline. Following this endocrine-mediated loss, there is a steady decline in bone density with advancing age.

Gender: Men have larger skeletons than women so their skeleton has a greater bone mass and hence greater mechanical strength. The pattern of bone loss differs between men and women, with women experiencing a phase of accelerated bone loss in the 10 years or so following the menopause.

Family history of osteoporosis: Genetic factors determine peak bone mass, and the timing and rate of bone loss in both sexes. It is thought that several susceptibility genes are involved. Maternal or paternal fragility fractures or kyphotic posture suggest the presence of a family history of osteoporosis.

Low body mass index (BMI): A BMI of ≤ 19 kg/mpredisposes the individual to osteoporosis.

Hormones: Premature menopause (in women under the age of 45) - whether natural or induced by surgery, chemotherapy, radiotherapy, or endocrine therapy - increases risk. Risk is increased in men who have had orchidectomy or androgen deprivation therapy.

Medical conditions associated with bone loss: These include rheumatoid arthritis, inflammatory bowel disease (e.g. Crohn's disease, ulcerative colitis), malabsorption (e.g. coeliac disease, pancreatic insufficiency), cystic fibrosis, hyperthyroidism, hyperparathyroidism, vitamin D insufficiency, immobilisation (e.g. resulting from CVA or Parkinson's disease), chronic obstructive pulmonary disease, diabetes mellitus type 1 and chronic renal and hepatic disease.

Drug treatments associated with bone loss: These include oral corticosteroids, aromatase inhibitors, androgen deprivation therapy, some anti-epileptic medications and glitazones.

Lifestyle factors: Smoking and alcohol intake ≥ 3 units per day increase osteoporosis risk.

What is the Impact of Osteoporosis?

The clinically important outcome of osteoporosis, fragility fractures, consumes vast health and social care resources. Conservative estimates suggest the total cost to the UK economy is in excess of £2.3 billion per year. For women over 60 years of age, fragility fractures account for more days spent in hospital than many other chronic diseases.

Hip fracture patients occupy more than one in five orthopaedic beds and the incidence of 89,000 a year is predicted to rise to 140,000 by 2036, causing substantial increased morbidity and mortality. Thirty percent of hip fracture sufferers die within 1 year and over 50% remain permanently disabled with an impaired quality of life, compounded by fear of falling.

Vertebral compression fractures are the commonest, often undiagnosed, osteoporotic fractures. Twenty to twenty-five percent of women will sustain a further vertebral fracture within 3 years and endure an increased future fracture risk at other sites. The impacts of vertebral compression fractures are significant, causing chronic back pain, limitation of activity and impaired quality of life.

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