Men's Osteoporosis Support GroupBone density vs bone quality Cleve Clin J Med. 2009 Jun;76(6):331-6. Bone density vs bone quality: what's a clinician to do? Licata A. PMID: 19487553. There is also free full text of this article which is aimed at clinicians treating osteoporosis and concerned with the importance of bone density vs bone quality. The majority of effort regarding osteoporosis concerns bone density as demonstrated by dual-energy X-ray absorptiometry (DXA). The T score is derived from DXA and is used by practitioners to determine if treatment is needed for low bone mineral density (BMD). Licata, however, explains that, "The T score as originally used was a surrogate marker for the histologic changes in aged bone that render it weak and susceptible to fractures from low loading forces: the lower the score, the worse the fracture risk." The problem comes when the T score is used on younger individuals, not in the original group of white women in their mid to late 60s and older, for which the test was developed. In such healthy young individuals, with what appears to be low BMD, the Z score should be used instead. This compares their BMD to age-matched individuals. The author explains that young bone is stronger than older bone at any T score. This because its quality is better. When studies are done to find fracture risk reduction after taking an FDA-approved osteoporosis medication, the changes in BMD only account for part of the fracture reduction. On page 334 there is a table showing, for several medications, the percent increase in BMD compared to the percent decrease in new fractures. There is often a much greater decrease in fractures than would be expected from the minimal increase in BMD. Osteoporosis therapy decreases the levels of bone turnover markers in a matter of weeks, whereas it may take years for increased BMD to show up. Thus the author states that, "Bones become stronger before they become denser." Thus a lack of change in BMD doesn't necessarily mean a lack of response to therapy. To determine the ultimate fracture risk, rather than just use the BMD and T score as the sole determinants of both bone density and bone strength, the author suggests using the FRAX, a fracture risk assessment tool developed by the World Health Organization. This is not entirely based upon hip BMD, rather it also takes into account patient age, sex, weight, height, whether the patient has a personal or family history of fracture, and whether the patient smokes, uses glucocorticoids, has rheumatoid arthritis, has secondary osteoporosis, or consumes excess alcohol. When you use this tool you'll know your 10-year estimated fracture risk. The author recommends that if fractures occur early in treatment, the patient should stay on the FDA-approved therapy. However, later fractures should cause one to start looking for secondary causes of osteoporosis, such as, vitamin D deficiency, hyperparathyroidism, or celiac disease. Also patients may not be compliant, a common problem. It may be necessary to switch to an intravenous form of therapy for poor compliance or malabsorption problems. Editor's comments. The bottom line is that bone strength is what ultimately determines fracture reduction. And it isn't always possible to determine, especially with DXA. If you are compliant with FDA-approved osteoporosis medication, your bone strength should be improved even if your BMD doesn't show improvement yet. Your risk of fracture should also be improved.
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