This is one of the main tools for detecting osteoporosis and other bone changes, especially in the lower spine, hip, forearm and heel.

These scans are particularly useful for establishing bone density and the likelihood of a future fracture. It is also used to detect bone infections and tumours.

Bone scans are better than X-rays for predicting hip fractures, but older patients may have difficulty manoeuvring into position. Bone scans don’t work on those with a previous wrist fracture or arthritis. Scans can also be misleading in people aged over 60, or if patients are either too thin or too fat.

A radioactive liquid is injected into the arm three hours before the scan. Scanning itself takes 30-50 minutes to do, while the subject lies flat on a table. A tomographic or SECT study may also be done on a particular area, taking an additional 30 minutes while the camera rotates around you.

While some radiologists see the scan as a vital and sensitive tool, studies have not always supported this view. It is useless, for example, in detecting prostate cancer if PSA levels are less than 10 ng/mL (J Urol, 1991; 145: 318-8; Br J Urol, 1997; 79: 611-4).

More worrying, bone scans were only able to detect bone deterioration in 19 out of 24 patients with known osteonecrosis, whereas magnetic resonance imaging (MRI) was able to identify all 100 per cent of them. Worse, the scan picked up only 39 lesions overall whereas MRI detected 89 lesions (66th Annual Meeting of the American Academy of Orthopedic Sur-geons, 1999).

It’s worth remembering that bone density and bone strength are not the same thing. Some drugs can increase bone mass by 5 per cent, but the damaged bone structure has not been strengthened.

Bone in a healthy individual is dynamic and constantly undergoing interior remodelling. So even if a future problem has been accurately predicted by a bone scan, exercise and a regime of supplements such as magnesium may do more to help the condition than any drug.