>>4243038Medfag here, this anon is correct.
Most likely this is a diabetic foot (almost everyone with late-stage diabetes is at risk for this sort of thing). The patient will lose feeling and the constant pressure from walking will create an ulcer which can then develop into gangrene. I've seen amputations up to the knee because of this sort of shit.
The rule of thumb for gangrene is you amputate 2 joints above the gangrene itself so as to stop the spread.
The other anons stating maggot therapy are also correct. This is used more commonly than you think when it comes to diabetic foot.