Ultimately, we need to compare apples to apples by building rating systems that account for the difficulty of treating patients with various, ailments at various ages, with various complications.

Think of it in terms of competitive diving, gymnastics, or snowboarding: Your scores depend upon the difficulty of the moves you attempted combined with your performance of those specific moves. The more difficult the move, the more you're compensated for even attempting it when it comes to scoring.

The trick then is to prevent physicians from gaming the system by exaggerating the difficulty of the patients they're dealing with. You'd need to use as many objective metrics as possible and possibly some system of having different physicians assess ratings than the ones performing the procedures - maybe in some kind of double-blind fashion to prevent any kind of coordination strategy.