Bone densitometry

Bone densitometry is a medical investigation which measures bone mineral density (BMD). In other words, it assesses the "solidity" of the skeleton. It can therefore be used to assess the risk of osteoporotic fracture, or fractures due to osteoporosis. Bone densitometry is also called dual energy absorptiometry or DEXA, for Dual Energy X-Ray Absorptiometryand is performed in a radiology centre. The investigation can be performed in a hospital in a radiology department or in a private rheumatology centre.

Bone densitometry - the process

Bone densitometry is indicated for patients who have signs suggesting ofosteoporosis particularly in the following situations:

• when a vertebral fracture has been discovered or confirmed radiologically, in the absence of traumatic factors (fall, etc);
• in people with a history of fracture occurring without injury, i.e. following a minor knock or simple fall from standing up;
• in early menopause (before 40 years old);
• in people with a family history of fractured neck and femur;
• in people with diseases or past history of diseases which cause osteoporosis (anorexia, hyperthyroidism);
• in people who are taking or have taken treatments liable to cause osteoporosis (for example long term corticosteroid therapy).

Note also that in some conditions bone densitometry is paid for in France by theFrench National Health Insurance Funds.

The bone densitometry procedure

The investigation is generally performed with the patient lying down on a bone densitometer. It uses low intensity X rays following a basic physical principle. It passes an energy beam through a solid body - a bone in this case - and measures the amount of energy released. The more thebone absorbs, the higher its density is and therefore the more solid the skeleton is. Measurements are generally taken in the lumbar spine or hip (neck of femur). The result obtained is called the T score.

Possible risks of bone densitometry

Bone densitometry is a painless investigation. The only risk is in the irradiation, which is extremely low dose. It represents a tenth of the dose delivered during a chest radiograph. Note, however, that the investigation is contra-indicated in pregnant women, patients who have had bone scintigraphy in the previous three days or an investigation of the gastro-intestinal tract in the last three days which has required a contrast medium.

Sources:

• www.rhumatologie.asso.fr, Société française de rhumatologie (French Rhumatology Society) website, accessed on 5 January 2011 ;
• French National Health Insurance Funds.