I hadn't heard of this procedure until about fifteen minutes ago, and I can honestly say that I have spent the last fifteen minutes having my mind blown thinking about this procedure.
It comes from an informational series with the Mayo Clinic which describes various medical procedures, their effects on the individual, and what life is like after undergoing them. This particular video covers rotationplasty, a thoroughly amazing operation that I'm still trying to wrap my mind around.
Basically, a rotationplasty is carried out by removing the middle part of somebody's limb, then taking the end piece, rotating it 180 degrees, and reattaching it to the body. In the example, the limb is a leg, so they end up removing the knee and affixing the person's rotated foot to their thigh. As a result, the individual can now use their foot as a knee...pretty amazing huh?
It's kind of difficult to conceptualize without the video, so I'll defer further explanation to youtube. This has to be one of the coolest medical procedures I've heard of.