Densitometry - test of bone density

Purpose of the study

Osteoporosis is a bone disease in which thinning occurs - a decrease in mineral density. This causes weakening and increased susceptibility to fracture. The lower the bone mineral density, the greater the risk of fracture. Thus, by measuring the bone mineral density, we can determine how much a person is at risk of fracture. Hence, the measurement of bone density - densitometry - is the basic diagnostic test for osteoporosis. We perform it primarily to check whether a person is at risk of breaking, and therefore whether he needs treatment. In patients undergoing treatment, the densitometry test is aimed at documenting the effectiveness of treatment.

Method description

Bone density testing - BMD (Bone Mineral Density) is performed using a densitometric device. A typical densitometric apparatus is built in such a way that a micro X-ray tube is placed under the table on which the patient is lying, and an arm of the apparatus with a radiation sensor is placed above the patient [fig. 1]. The test is completely safe. The radiation dose is harmless – it is – 2.0 mSv. This dose is received by each of us with cosmic radiation during 4 hours of being outdoors.

Test result - diagnosis

Based on the T-score values, WHO has developed diagnostic categories for osteoporosis. An index value from +1 to -1 means normal, between -1,1 and -2,4 osteopenia, and from -2,5 or less osteoporosis. If a person has a score of -2,5 or less and has a fracture, we can diagnose severe osteoporosis.

What kind of densitometry test do we perform?

The optimal solution is to simultaneously examine the hip (proximal end of the femur) and the spine. The advantage of examining the spine is that osteoporotic changes appear here as early as possible and the results of treatment are visible as soon as possible. However, the problem of spine examination are degenerative changes appearing with age, which may significantly distort the examination result.

The advantage of the hip examination is that the measurement does not change with age, while changes here appear relatively late, most often the result of the hip examination is much "better" than the spine examination. An additional argument for the measurement of the hip is that the densitometry test "predicts" a fracture in the place where it is performed, and the most dangerous osteoporotic fracture is a hip fracture.

The optimal solution is to perform tests at both measurement sites, because each of them has its own advantages. Densitometric examination is performed as a standard in annual periods. The most accurate measurement result is obtained by performing the test on the same apparatus or on the apparatus of the same type. Studies on different devices are unfortunately incomparable, because they use different measurement methods and have different control groups.

Final recognition

Decreased BMD requires additional analytical tests to determine its cause. In women, the most common cause will be postmenopausal osteoporosis, but it can also be the result of other diseases, such as hyperthyroidism or parathyroidism, gastrointestinal diseases, or taking medications. For this purpose, before starting treatment, it is necessary to perform analytical tests to treat the cause and not the effect, i.e. lowering BMD.

Densitometric examination and fracture risk – FRAX method

It should be remembered that a decrease in BMD is the strongest indicator of fracture risk, but a normal result does not rule it out. Just as an abnormal ECG result may indicate the risk of a heart attack, but a normal result does not rule out the occurrence of a heart attack. In practice, it turned out that 70% of fractures occur in people with normal bone density. This problem is solved by the FRAX method published by WHO in 2008. The basis of this method is the calculation of the absolute risk of fracture by integrating the various factors that influence it. The method takes into account age, sex, body mass index - BMI, history of fractures, hip fracture in parents, smoking, use of glucocorticoids, RA, secondary osteoporosis and alcohol abuse. FRAX calculates the 10-year absolute risk of hip fracture and major osteoporotic fractures. In Poland, it is assumed that the FRAX values ​​for major fractures mean the following risk: below 5% - low, 5-10% - medium and above 10% - high. The method is available online at www.osteoporoza.pl. Calculations can be made without leaving home based on BMI, calculated on the basis of weight and height. program available www.kcm.pl

Detection of spinal fractures (VFA – Vertebral Fracture Assessment)

The modern densitometric apparatus at KCM's disposal also allows for the examination of the thoracic and lumbar spine to detect possible fractures. It should be emphasized that 60% of spinal fractures go undiagnosed because they do not cause any symptoms. The only symptom may be a decrease in height of about 4 cm or more. X-ray irradiation in the densitometric examination is 40 times lower than in the radiological examination (morphometry DXA 41 mSv, radiological 820 mSv). In addition, the examination can be performed immediately after the completion of the spine and hip examinations.

Bone structure analysis

The KCM densitometry laboratory is equipped with an additional program "Trabecular Bone Score - TBS", approved by WHO in 2012 for the diagnosis of osteoporosis. The program analyzes the structure of the trabecular bone of the spine. Thanks to this, we obtain more information about its quality, risk of fracture as well as about the effects of treatment. The TBS program increases the precision of FRAX fracture risk assessment, which we use in our research.

WHOLE BODY COMPOSITION TEST

Our device also allows you to analyze the composition of the muscle and fat mass of the whole body. The test gives precise information about the size and distribution of adipose tissue and muscles. It is indicated in the study of obesity and muscle mass disorders, which is important, e.g. in assessing the risk of falling.

 

Dig. Fig. 1: Spinal densitometry examination with the Hologic apparatus

 

Dig. Fig. 2: Sample printout of the densitometry examination of the spine

Details:

  1. a) thumbnail of the printout,
  2. b) test results, fourth column from the left BMD:

– total measurement (vertebrae L1-4) – BMD 0,610 (gr/cm2),

– T – score – 4.0; Z-score - 2,3,

  1. c) illustration of the normal range: BMD value on the vertical axis/age on the horizontal axis,

patient score marked at 63 years.

  1. d) picture of the densitometric examination of the L1-L4 vertebrae.

 

Dig. 3 Example of morphometric examination of the spine - DXA
The camera marks the height measurement points: back, middle and front.
A 20% decrease in vertebra height is considered a fracture.
Diagnosis: Wedge fracture of the Th6 vertebra and biconcave fracture of the L-2 vertebra.

 

Dig. Fig. 4: An example of bone structure assessment with the Trabecular Bone Score program
The density test result is the same in both cases (T -2.0), but the structure on the left is normal (index 1,4) and on the right is disturbed (index 1,2), which means an increased risk of fracture.

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