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Osteoporosis is a bone disorder caused by loss of bone mass resulting in abnormal bone structure and an increased risk of fracture.
Female skeleton degenerating due to osteoporosis.

Computer artwork of a human female skeleton degenerating due to osteoporosis. At left is a normal skeleton. The degeneration, seen from left to right over time, is the loss of height and the backwards curvature of the spine.

What is osteoporosis?

Osteoporosis is a loss of bone matrix (osteoid) and bone minerals (calcium and phosphate) that make bone rigid.  This means that bones become less strong and are more prone to fractures.  It is different from rickets (osteomalacia), as seen in vitamin D deficiency, when there is simply a loss of bone mineral.  Osteoporosis is the commonest acquired bone disorder and cause of fractures in adults. 

What causes osteoporosis?

Bone is continually being broken down and built up (bone remodelling) but in osteoporosis there is an excessive breakdown of bone that outstrips bone production.  The greatest amount of bone mass is reached between 20-30 years of age and this then declines slowly after around the age of 40 in both men and women.  If bone mass declines to reach a certain level, then osteoporosis is diagnosed.  This means osteoporosis occurs mostly in older people.  Most osteoporosis has no specific cause (primary osteoporosis) but there are a number of reasons why some people are more likely to have osteoporosis than others. 

Oestrogen deficiency, normally as a result of the menopause, is the commonest contributor to osteoporosis, although other secondary causes can also result in osteoporosis.  These can include various endocrine disorders such as: 

Other secondary causes include:

  • Rheumatological diseases
  • Chronic kidney disease
  • Drugs such as steroidal anti-inflammatories and some anti-epileptic drugs
  • A few inherited disorders such as brittle bone disease (osteogenesis imperfecta) or even cystic fibrosis    

There are also lifestyle factors that can affect the risk of developing osteoporosis.  For example, smoking, drinking excessive alcohol and not exercising increase the risk of developing osteoporosis, as does being underweight.  Regular exercise and a healthy diet that includes an adequate amount of calcium and vitamin D are ways of reducing the risk of developing osteoporosis.  Vitamin D can also be manufactured by the skin when exposed to sunlight. 

What are the signs and symptoms of osteoporosis?

Osteoporosis has no symptoms (asymptomatic) until complications occur.  Any fracture that occurs following minor injury should raise suspicion of underlying osteoporosis.  The most common fractures that occur in osteoporosis are those of the hip, wrist and spine bones (vertebrae), although fractures can occur at any site.  Usually, fractures of the hip and wrist occur after a fall, but fractures of the vertebrae may occur without any obvious injury.  Such fractures may not cause any symptoms or are accompanied by the development of acute back pain which may disappear over weeks or months.  Multiple fractures of the spine can cause loss of height and significant spinal deformities and patients may develop marked abnormal curvature of the spine (kyphoscoliosis - see figure above). 

How common is osteoporosis?

About half of women and almost 20% of men over the age of 50 will have a fracture from osteoporosis (osteoporotic fracture) at some point in their lifetime.  Vertebral and hip fractures are the most commonly encountered.  However, although the chances of having a hip fracture increase as age advances, only about 0.3-0.5% of women over the age of 75 will suffer from a hip fracture.  This increases to about 1% of women over the age of 85.  More women than men tend to have fractures of the hip. 

Is osteoporosis inherited?

There is a tendency for osteoporosis to run in families, but the inheritance of a specific gene or genes has not yet been identified.  This means individuals may inherit a greater likelihood of developing osteoporosis, but if one of the parents is affected, it does not necessarily mean that the children will develop the condition. 

How is osteoporosis diagnosed?

Diagnosis of osteoporosis is usually made by measuring bone density with dual energy X-ray absorpimetry (DEXA scanning) and, routinely, this will be done on the hips and vertebrae.  In severe osteoporosis, bones may appear thin even on simple X-rays and these may also show fractures in vertebrae, but there is very rarely, damage to the spinal cord.  

Blood tests are also carried out to look for evidence of secondary causes of osteoporosis and these include measurement of bone biochemical profile, thyroid function and parathyroid hormone.  Where appropriate, testing for other secondary causes should also be undertaken.  Usually in primary osteoporosis, these blood tests, by definition, are normal. 

How is osteoporosis treated?

The major class of drugs used to treat osteoporosis is bisphosphonates.  These drugs collect in bone matrix, where they can enter bone cells and prevent the cells breaking down bone, causing excessive loss of bone mass.  They have been shown to reduce the risk of both hip and vertebral fractures.  The most commonly used bisphosphonates are risedronate and alendronate, which are normally taken once weekly.  Zoledronic acid may also be used and is given as a once-yearly infusion. Vitamin D and calcium should be replaced in all patients starting treatment for osteoporosis as they may be deficient in these.  

Oestrogens (such as those found in hormone replacement therapy) can also be given to treat postmenopausal osteoporosis, although long-term use is no longer recommended and it is usually only prescribed for treating menopausal symptoms.  Other drugs which may be used to treat osteoporosis include strontium ranelate (taken by mouth), denosumab (injected) and parathyroid hormone (injected).  

Are there any side-effects to the treatment?

The side-effects of taking bisphosphonates, if any, are usually mild and can include indigestion, a change in bowel habits (constipation or diarrhoea), tiredness, feeling sick and mild flu-like symptoms.      

What are the longer-term implications of osteoporosis?

The long-term implications of osteoporosis are the increased risk of fractures from minor injury.  Immobility caused through these fractures can also have long-term consequences because it reduces physical ability, particularly in the elderly.  Exercise is important in building bones, making it important for all patients with osteoporosis to have regular exercise, particularly weight bearing and resistance exercise.  Patients should also try to maintain a healthy lifestyle and diet.  Alcohol and smoking are also risk factors for osteoporosis and their use should be discouraged.     


Written: March 2011