Bone mineral density (BMD)

Dual-energy absorptiometry (DXA) is the single most common chosen and preferred technique for measurement.

Dual-energy absorptiometry (DXA) can easily measure BMD at multiple skeletal sites with minimal radiation exposure.

Results are presented in g/cm2.

Can assess fracture risk, diagnose osteoporosis come and monitor skeletal effects of medications that reduce fracture risk.

It is underused test.

Assumes the presence of a homogenous distribution of minerals and density and does not reflect variability of bone microarchitecture.

Z score is the standard deviation score representing the difference between the obtained BMD and the BMD of a normal population at comparable age.

Normal BMD defined as a T score greater than -1.0, osteopenia between -1.and-2.49 and osteoporosis associated a score equal to or less than -2.5.

Is a measure of the amount of bone mineral mass within a user defined area but is confounded by bone size, which is a determinant of bone strength.

Accrual of bones mineral density during childhood and adolescence is critical to establish sufficient bone mass to be able to support and maintain skeletal health throughout life.

Is higher if a bone is bigger, even if the degree of mineralizaton of the bone is the same.

Fracture risk doubles for each standard deviation reduction in BMD.

WHO risk assessment tool (FRAX) fracture risk-combines BMD and other factors including age to provide 10 year estimates for fracture.

A prospective analysis suggested that repeating a BMD measurement up to eight years after initial screening provides little additional value for predicting the fractures in elderly women (Study of Osteoporotic Fractures).

Women can lose as much as 20% of bone density in 5-7 years postmenopausally.

 

The average BMD loss is 0.5-1% per year.

The time from a prior BMD examination to the development of osteoporosis is about 17 years for women with normal BMD and mild osteopenia, about 5 years for women with moderate osteopenia, and about 1 year for women with advanced osteopenia.

In a study of 4957 women, 67 years of age or older, with him BMD or osteopenia with no history of hip or vertebral fracture or treatment for osteoporosis were followed prospectively for up to 15 years: osteoporosis would develop in less than 10% of older, postmenopausal women during re-screening intervals of approximately 15 years for women with normal bone density or mild osteopenia, five years for women with moderate osteopenia, on one year for women with advanced osteopenia (Gourlay ML et al).

Screening intervals should be determined by baseline bone density and retesting intervals should be relatively infrequent in patients with normal or near normal bone density at baseline.

It is reasonable to rescreen postmenopausal women whose initial bone density are in the normal range in 10 years, providing they do not have additional factors associated with increased risk of fracture or acceleratedthe rate of bone loss.

Patients with mild osteopenia and low FRAX estimated fracture risk should be screened and 5-10 years, in women with marked or more advanced osteopenia or with FRAX estimating fracture risk near the intervention threshold should be rescreened in two years.

Recommended therapeutic intervention for FRAX risk of 3% for hip fracture at 10 years and more than 20% for all major fractures.

Evidence for genetic contribution to variation in bone mineral density estimated between 0.6-0.8.

T score is the standard deviation score computed to be the difference between the obtained BMD and the BMD of a young normal population at peak BMD.

T score represents the risk of fracture.

Can also be assessed by quantitative CT analysis, but is associate with higher radiation exposure and is more costly than dual-absorptiometry.

Quantitative CT permit’s a 3-dimensional assessment and allows for the measurement of orbicular bone density and bone architecture itself.

Is a better predictor of fractures than blood pressure is of stroke, with a relative risk of hip fracture 2.6 for each 1 SD decrease in bone mineral density at the hip.

Decreases by approximately 2% annually for the first 5 years after menopause and 1% per year subsequently.

Bone density decreases faster in the spine than in the hip.

In a study of nearly 10,000 men and women calcium intake was unrelated to bone mineral density at the hip (Bischoff-Ferrari HA).

Men lose bone mass at a rate of 0.5% to 1% per year after the age of 35 years.

Testing recommended for women 65 years or older, women 45 years of age or older who weigh less than 60 kg, and women 55-64 years of age who weigh 60-70 kg and are not taking estrogens.

Decreased bone mineral density associated with depression.

Directly associated with cardiorespiratory fitness.

Patients with late menarche, early menopause and low endogenous levels of estrogens have decreased bone mass.

Reduced in patients with anorexia nervosa.

Correlated with lifetime exposure to circulating estrogens.

Positively associated with levels of endogenous estrogens, particularly estradiol, and negatively associated with sex hormone binding globulin.

Elevated bone density associated with higher risk of breast cancer.

Decreased by use of antiepileptic drugs.

The interval development of an osteoporotic bone density is a indication for treatment, as would a new fragility fracture.

Many risk factors for fractures are independent of bone density, the most important is the age of the patient.