According to a quick Google search, there are 185,000 amputations in the United States each year. The top causes are vascular disease (53%), trauma (45%), and cancer (2%). By the 2070s, we can safely assume that the corporate elite can afford cloned replacement limbs, but why not turn a disability into an advantage with top-of-the-line cyberware? Less fortunate people settle for off-the-shelf models and upgrade when and how they can, while the disenfranchised make do with secondhand limbs (pun intended).
Don't forget military backgrounds. Wounded in action doesn't have to mean a medical discharge in the 2070s. They can rebuild you ... better, stronger, faster. Major corporate and national militaries can afford state of the art. I expect most modern combat units will have a couple or three soldiers with cyberlimb replacements.