Within the bone densitometry have accommodated a number of rapid tests, non-invasive and painless that help the diagnosis, prognosis and treatment monitoring of osteoporosis.
1. What is osteoporosis?
Osteoporosis is a disease characterized by reduced bone strength that facilitates the occurrence of fractures. One of the key elements that resistance is the bone mass (BM).
The decrease of OM has been associated with the occurrence of future fractures, so far this decline has been considered a predictor of fracture risk.
In clinical practice, the operational definition of osteoporosis that is used is the WHO (World Health Organization, 1994) based on the extent of MO as bone densitometry (DO).
2. What is bone densitometry?
It is a method of diagnosing and monitoring the state of bone mass. This is by quick tests, non-invasive and painless.
2.1. Absorptiometry bone
Bone X-ray absorptiometry or dual-energy dual (DXA or DEXA) is usually performed in hip and lower spine veretebral.
The currently most widely used techniques are based on ionizing radiation, and one of the most widespread is the bone X-ray absorptiometry or dual-energy dual (DXA or DEXA). It is an improved variation of the X-ray shows osteoporosis only when you have a bone loss exceeding 30%.
The DEXA is usually performed in the hip and lower spine veretebral. The duration of the DXA scanning between 5 and 20 minutes and the radiation dose is minimal (5-10 mrem), usually less than that received in a chest radiograph. Their values are expressed in grams per cm2 and are valued at two comparisons:
- By comparison with the values of people of similar age, size and sex.
- Compared with those values where the MO is higher (peak bone mass) which is usually between 20 and 30.
This technique allows not only define osteoporosis according to WHO criteria, but also monitor changes in the MO and establish the risk of fracture. It is also effective in monitoring the effects of treatment of osteoporosis and other diseases where there is bone loss.
It has been found that the decrease in OM is the main factor, but not the only one that determines the risk of fracture. Patients with osteoporotic fracture MO are worth less than those without fracture, but even so there is some overlap in the extent of MO in patients with osteoporotic fracture and patients of the same age and sex without osteoporotic fracture. Other factors that could influence the onset of osteoporotic fracture, are included within the concept of bone quality such as changing the architecture and elasticity of bone. Therefore, the ideal technique would be one that measures both bone quantity and bone quality.
2.2. Ultrasound
Ultrasonic bone densitometry, often performed in the calcaneus. Ultrasound (U.S.), are non-ionizing technique for measuring the MO, but have yet to establish its clinical utility and precise.
This is a technique that requires little setup, cheaper (and therefore can offer more accessibility than ionizing techniques), which does not radiate, and requires little time to scan (about 5 minutes). Moreover, it appears that not only provides information on the density but also bone architecture and elasticity. It is for these reasons that it has raised its possible use as a screening technique prior to the above.
The calcaneus was the most used location for exploration with the U.S., since it has a porous or cancellous composition at 95% and also by their morphology, because it is a flat bone, symmetrical, easily accessible and allows precise and accurate location of transducer repeated measures.
Yet every U.S. business model in the market applies to a particular location (calcaneus, tibia or phalanges basically), use a particular means of transmission (water or gel), and allows certain parameters such as mitigation of the U.S. (Broadband Ultrasound Attenuation, BUA) and speed of the U.S. (Speed of Sound, or SOS).
There are manufacturers who have attempted to provide its model parameters most understandable from a clinical point of view, resulting from combinations of BUA and SOS, as the index of rigidity (Stiffness Index, SI), or the quantitative index of U.S. (Quantitative Ultrasound Index, QUI).
Despite growing interest in the use of bone densitometry by ultrasound for diagnosis / screening of osteoporosis, it seems that there is little evidence yet on the usefulness of the U.S. outside the context of the investigation or the use of pre-screening DXA.
3. Does the patient prepared in a special way?
The patient coming through densitometry, as absorptiometry and ultrasound, no need to go on fasting. The only condition is not ingesting calcium supplements 24 hours before testing.
If done absorptiometry, as we have seen that uses radiation and is usually done in hip or spine, you should remove your clothing, keeping only underwear that does not have any metallic element and be provided with a gown.
It should also remove jewelry, glasses, etc.. If you have performed a CT scan that required a barium contrast medium injected, will miss 10 to 14 days until the completion of the densitometry. As a test that uses radiation, its use should be avoided in pregnant or who believe they may be.
