Bisphosphonates & Atypical Femur Fractures: Part 2

Remember my December 10th post about bisphosphonates?  Of course, you don't.  That's ancient history, at least by medical standards.  Well, here's the latest chapter, which needs to be entitled "Relative Risk vs Absolute Risk".  Just released this past week in JAMA, in a population-based, nested case-control study of 205,466 Canadian women >68yo, the authors concluded that use of bisphosphonates increased (more than doubled) the risk of atypical subtrochanteric or femoral shaft fractures after 5yrs of use compared to non-users.  But this is relative risk.  The absolute (or true) risk was actually quite low, only 0.35% or 716 women.  

And lest you decide to stop taking your bisphosphonate because of a misguided fear of this rare fracture type due to misinterpretation of statistics, the authors also found 9723 women who'd sustained a more typical femoral neck or intertrochanteric fracture despite bisphosphonate use, which actually lowered the relative risk of fracture by 24% after taking the usual suspects into account.

Let me put it another way and give you a different example.  Let's say the risk of something bad happening was 4 out of 100 or 4%.  If you took some medicine that could lower your risk to 2 out of 100 or 2%, you would have achieved a 50% relative risk reduction.

Likewise, let's say the risk of something else bad happening was only 4 out of 1,000 or 0.4%.  And if you took some medicine, you could lower your risk to 2 out of 1,000 or 0.2%.  In reality, you would've achieved the same 50% relative risk reduction.

So while it may sound impressive in both situations to claim that you lowered the relative risk of a bad occurrence by 50%, in actuality, the absolute risk reduction was minimal in the 2nd scenario.

Returning to our situation with bisphosphonates, prolonged use >5yrs might double the risk of a rare fracture while truly minimizing your risk of a more common fracture.  As a result of this study and the others already mentioned 2 months ago in my earlier post, it appears the consensus is moving towards limiting bisphosphonate use to just 5 years.  We'll see whether that actually becomes a guideline shortly.  In the meantime, as with all new findings, please discuss your individual situation with your family physician before abruptly stopping some regimen based upon the lay press.