OSTEOPOROSIS
You review a 67-year-old woman in the fracture clinic. She has had a distal radius fracture after a fall. The fracture is in a good position and you have agreed that she will be treated in a cast. She asks if she should be taking something for ‘weak bones’.
- What advice would you offer?
I would take a targeted history from this woman, looking to identify the energy of her injury: It appears to be a low-energy fall. I would also explore any potential risk factors for osteoporosis or osteopenia. Her fixed risk factors include age, sex, family history of osteoporosis and her ethnicity. Modifiable risk factors include current or previous frequent use of steroids, premature menopause or ovarian failure as well as alcohol and cigarette use. In a female patient over the age 65 years or a man over the age of 75 years with one or more of these risk factors, the risk of osteoporosis and resulting fragility fractures is increased and bone protection may be appropriate.
I would suggest that the patient is investigated with a bone mineral density scan. In my hospital, patients are referred for this routinely based on screening of fracture clinic referrals and the results are passed to the general practitioner who is able to decide on appropriate management or referral with the patient.
- What are the key outputs from a DEXA scan and how would you interpret these figures?
The DEXA scan produces a measure of bone mineral density (BMD) expressed as two figures, the T-score and the Z-score. Both are expressed in units of standard deviation. The T-score compares the patient bone mineral density to that of a healthy 30 year old of the same sex and ethnicity. This is the most important score. The Z-score is an age-matched score comparison. It allows comparison of bone mass with patients of the same age, sex, race, height and weight.
If the T-score is greater than –1 SD, this is normal. Osteopenia is diagnosed when the T-score is between –1 and –2.5 SD. Osteoporosis is diagnosed with a T-score of –2.5 SD or below. A Z-score of –2 SD or below indicates a lower bone mineral density than expected for a healthy adult of the same age.
While these investigations give a measure of bone mineral density, the fracture risk for a patient is also affected by factors such as a history of falls or previous fracture. These should be considered with the bone mineral density results when determining if bone protection is appropriate. The World Health Organisation Fracture Risk Assessment Tool (FRAX) is one way of making this assessment.
Local practice in my hospital is based on NICE guidance. Post-menopausal women and men over the age of 50 with a T-score of –2.5 or less are, after appropriate counselling, recommended to be prescribed a bisphosphonate. Where dietary calcium intake is adequate, supplementary vitamin D is recommended if sunlight exposure is limited. Hormone replacement therapy is considered for women who suffer premature menopause.
3. Can you tell me about the agents used for the treatment of osteoporosis and explain how these act?
There is formal NICE guidance for this. All patients diagnosed with osteoporosis or who are at risk of fragility fracture should receive general lifestyle advice.
- Patients are prescribed vitamin D (800 IU) and calcium (1500 mg) supplements daily.
- Bisphosphonates: These are the most common pharmacologic agents used. They inhibit osteoclast activity by attaching to the ruffled border of the osteoclast and so reduce bone resorption. There are risks associated with the use of bisphosphonates; atypical proximal femoral fractures and osteonecrosis of the jaw have been described. Both are rare but the risk of femoral fracture particularly means that it is recommended that bisphosphonate treatment should be reviewed with a repeat fracture risk assessment after 5 years of treatment. Patients who remain at high fracture risk or who have very low BMD are recommended to continue lifelong treatment. Where the fracture risk has improved or a repeat bone scan shows a T-score at or close to –2.5 then a ‘treatment holiday’ of 1–2 years may be advised in order to reduce the risk of proximal femoral fracture.
- Strontium ranelate is a second-line drug and acts by activating osteoblasts and encouraging bone production.
- Oestrogen receptor modulators such as Raloxifene attach to oestrogen receptors in bone and encourage bone formation.