Osteoporosis is a very common disease caused by loss of bone. The bones become thin and are thus much more liable to fracture.

Causes

The maximum amount of bone in the skeleton (peak bone mass) is achieved soon after linear growth ceases, usually in the late teens. Peak bone mass is largely determined by genetic (inherited) factors, and thus a family history of osteoporosis may signify increased risk for developing the disease.

The skeleton is kept healthy throughout life by processes which remove old bone tissue and replace it with new bone tissue. The two processes of bone breakdown and bone formation usually balance each other so that bone is neither lost nor gained. Bone loss, which may result in osteoporosis, occurs when the process of bone breakdown exceeds that of bone formation. Bone loss occurs in all women following the menopause, and postmenopausal osteoporosis eventually affects 1 in 3 women. In men, bone loss occurs gradually with aging.

Other causes of osteoporosis include overactive thyroid or parathyroid glands, certain cancers and leukaemias, rheumatoid arthritis, and treatments such as corticosteroids. Osteoporosis is less common in men, but can be due to lack of testosterone.

Effects

Bone loss itself does not cause any symptoms, and people losing bone for any reason are not aware of it. Fractures most commonly occur in the spine, wrist and hip, but can also occur in the ribs, pelvis, shoulder and ankle. Fracture causes immediate and often quite severe pain at the site. This pain can persist for several weeks but eventually resolves. More persistent pain, usually in the back, is usually due to bony deformity which produces a local arthritis, or sometimes due to microscopic fractures continually occurring.

Osteoporotic fractures usually heal quite normally. Hip fracture is the most important osteoporotic fracture because it requires hospitalisation and usually a surgical operation, and it carries an increased early death rate.

Diagnosis

Osteoporosis may be suspected in someone who sustains a fracture after fairly minimal trauma. An X-ray may reveal the presence of spinal fractures but osteoporosis is often difficult to detect on plain X-rays in those who have not yet fractured.

The best diagnostic procedure is to have a measurement of bone mineral density. This is performed on a dual-energy X-ray absorptiometry (DEXA) machine. It is a non-invasive procedure which takes just a few minutes to perform, and gives an almost negligible radiation exposure. Other procedures, such as using ultrasound (sound-wave) assessments are less reliable.

Treatment

Diet and exercise alone are not able to prevent or treat osteoporosis. Most treatments for osteoporosis are with drugs that reduce bone breakdown, and hence prevent bone loss. When such drugs are first given, there is often a gain in bone mass, because the reduction in bone breakdown exceeds that in formation, and thus a “positive” bone balance exists for some years. There are now some drugs which primarily increase bone formation rather than just reducing breakdown.

Bisphosphonates are drugs which prevent bone breakdown. They are usually given as a once weekly tablet, although newer drugs can be given as an intravenous injection every few months. They are very effective in reducing the risk of fractures in people who have got osteoporosis.

Hormone replacement therapy (HRT) prevents bone breakdown, and may also increase bone formation to some extent. It is very effective in preventing the development of osteoporosis and fractures in postmenopausal women. It is usually given to those identified as being at increased risk, and is more effective than any other currently available treatment. It can also be used for the treatment of osteoporosis in women who already have the disease.

Strontium ranelate is a powder that is given on a daily basis to prevent fractures in people with osteoporosis. It both reduces bone breakdown and increases bone formation.

Calcitonin is a drug which reduces bone breakdown. It has a weaker effect than most other drugs, and does not reduce the risk of hip fractures. It has to be given by daily injection under the skin (a nasal spray is not available in the UK). It may also help relieve pain from osteoporotic fractures, but it is expensive and not widely used.

Teriparatide is a drug which increases bone formation quite dramatically, and thus reduces fractures in those with osteoporosis. It has to be given by daily injection under the skin, and is very expensive.

Selective estradiol receptor modulators (SERMs) are drugs which act like weak oestrogens in some tissues and like anti-oestrogens in other tissues. They can prevent and treat osteoporosis in postmenopausal women, but do not prevent hip fractures.

Anabolic steroids may reduce bone breakdown and increase bone formation, and can be used for treatment of osteoporosis. They usually have to be given by injection into a muscle every 3 weeks, and have a number of side-effects which precludes their widespread use.

Calcium ± vitamin D is not effective by itself for either the prevention or treatment of osteoporosis and fractures (except in the very elderly and housebound individuals), but is used as an adjunct in certain situations, such as in patients taking corticosteroids.

 

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