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Bisphosphonates & Atypical Femur Fractures: Part 4

Posted May 16 2011 8:30am
Earlier this month, the New England Journal of Medicine jumped into the growing controversy in osteoporosis management by publishing a case-control study that concluded that (current) use of bisphosphonates increased one's risk of atypical femur fracture by almost 50 fold.  With such a dramatic increase in risk, many of the major news outlets had to weigh in, including USA Today .

However, as usual, the devil is in the details and what was left out of the sensational reporting is the relative infrequency of these atypical fractures.  In fact, use of bisphosphonates would lead to an additional 5 atypical fractures for every 10,000 patient-years of use.  Put another way, we'd have to treat 2,000 patients in order to harm 1 (also known as number needed to harm).

On the other hand, the number of patients needed to be treated in order to prevent just 1 typical osteoporotic fracture is dramatically less.  In other words, use of bisphosphonates in patients w/osteoporosis is of net benefit.  However, the same cannot always be said for those w/osteopenia or low bone mass.

So know the strength of your bones before you start the medication.  In fact, to be sure that you really need this medication, ask your doctor to use the WHO Fracture Risk Assessment Tool, FRAX, to  calculate your 10 year risk of sustaining an osteoporotic fracture  after measuring your bone mineral density via DXA (dual energy xray absorptiometry).  Those who are osteoporotic with a T score < -2.5 warrant therapy while those who are osteopenic w/T score between -1 and -2.5 warrant therapy if their 10 year probability of a hip fracture is > 3% and/or their 10 year probability of any major osteoporotic fracture is > 20%.  Be sure your calculation is based upon data appropriate for your ethnicity!

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