Blame it on Congress

According to the New York Times:

Congress, while allowing Medicare to spend billions of tax dollars on medical devices, effectively bars it from collecting data showing how well competing products work.

Interestingly,

The Food and Drug Administration requires makers of defibrillators and pacemakers... to report detailed product performance annually, but it does not make those reports public.A doctor's decision to use a particular manufacturer's artificial hip or pacemaker is often based on subjective factors. Often, physicians will choose the makers' devices on which they were trained or ones they are used to using.

And as I've pointed out before, the choice of orthopedic devices in particular is often influenced by unseemly relationships between sales reps and surgeons, greased by outsized "consulting" contracts.