OSTEOPOROSIS & BONE MINERAL DENSITY (BMD) MEASUREMENT

What is Osteoporosis?
Osteoporosis is a reduction in volume or mass of normal bone, which results in a decrease in bone strength and fracture. Bone loss involves the entire skeleton. However, it is more common in certain bones such as the backbone (spine), the hip (proximal femur) and the wrist (distal radius). Hip fractures are especially important because they are associated with mortality rate of up to 10%. These fractures are becoming more common now because the world’s population is aging.

Osteoporosis is commonly seen among postmenopausal women. This is related to the decrease in female hormone (estrogen) secretion. Studies had shown that osteoporosis is four times more common in postmenopausal women than men. Osteoporosis can also occur in the elderly (senile osteoporosis) and in association with hyperparathyroidism and Cushing disease, corticosteroids usage, prolonged inactivity, and nutritional deficiencies.

There is usually no symptom in the early stages of osteoporosis. Fracture is usually the first clinical presentation. Treatment is currently available for those individuals who are at risk for developing osteoporosis or fracture. Identification of high-risk individuals by bone density measurement is crucial as little can be done to restore lost bone in older osteoporosis patients.

What is Bone Mineral Density (BMD)?
The only sure way to determine bone density and fracture risk for osteoporosis is to have a bone mass measurement (also called bone mineral density or BMD test). Estimation of fracture risk by BMD measurements is similar to the assessment of the risk of stroke by blood pressure readings. The bone density is compared to two standards known as “age matched” and “young normal”. The age-matched reading compares the bone density to what is expected in someone of the same age, sex and size. The young normal reading compares the density to the optimal peak bone density of a healthy young adult of the same sex. Depending on the result, individuals may be grouped as:

• Normal
• Osteopenia (low bone mass)
• Osteoporosis
• Severe osteoporosis

This information enables the doctor to assess fracture risk and to decide the best possible treatment.

What is the relationship between BMD and fracture risk?
In general, the lower the bone density, the higher the risk for fracture. In individuals with low bone mass, there is a 2 to 3 fold increase in the incidence of spinal fractures. In individuals with a BMD in the osteoporosis range, there is approximately a 5 times increase in the occurrence of fractures.

Why is BMD measurement important?
Determining an individual’s BMD helps a doctor decide if treatment for osteoporosis is needed. In addition, if therapy is started, subsequent BMD measurements can monitor the effectiveness of treatment. The purpose of BMD testing is to:

• Help predict the risk of future fracture
• Measure the amount of bone mass
• Monitor the effectiveness of treatment

What are the methods of Bone Mineral Density measuremet?
There are several methods used to measure bone mineral density.

• Single Photon Absorptiometry
• Dual Energy Photon Absorptiometry
• Dual Energy X-ray Absorptiometry (DEXA)
• Quantitative Computed Tomography
• Quantitative Ultrasound

Among all these techniques that have been developed, DEXA is most widely used and regarded as the gold standard for bone mineral density measurement.

Who should be screened?

• Postmenopausal women
• Premature menopause (<45 years old)
• All individual aged 65 and older regardless of risk factors
• Previous fragility fracture especially of the spine or wrist
• Individual with vetebra abnormality
• Thin or small built individuals
• Hyperparathyroidism
• Individuals with prolonged corticosteroids or thyroid treatment
• Cushing disease
• Prolonged inactivity or inactive lifestyle
• Nutritional deficiencies
• Primary hypogonadism
• Post-transplantation
• Chronic renal failure
• Individuals on treatment of osteoporosis

How is a standard examination performed?
There is no preparation required for this examination and it is completely painless, noninvasive and safe. Individuals need to lie still for 5-10 minutes for this procedure. A standard examination includes imaging of the spine, hip and/or wrist. The total examination period is about 10 minutes and complete report will be ready in about one hour.

What is the radiation risk?
The radiation dose from the procedure is only about 1/20 of that from a routine chest X-ray and 1/1000 of that from a routine spine film.

How frequent should the examination be repeated?
Generally, the examination should be repeated every two years. However, in certain medical conditions, a more frequent examination may be needed.

What are the restrictions?
Restrictions to the examination include

• Recent barium study
• Recent administration of radionuclides
• It is not recommended during pregnancy
• Metalic or radio-opaque implants at the site to be measured
• Marked Obesity. The upper weight limit is 270 lbs (123kg)
• Extremely low BMD