The death of tissue due to lack of blood supply is called gangrene.
Lack of blood supply can be because of stoppage of blood supply due to blockage in the blood vessels due to acute or chronic causes.This is the so called DRY GANGRENE. Acutely, thrombosis or embolism can occur. However chronic factors can be due to smoking, diabetes, hypercholesterolemia etc which leads to plaque formation in the arteries and cut off of supply.However chronic causes usually do not lead to sudden whole limb gangrene unless an acute process like sudden thrombosis or embolism occurs. This is because with slow blockage especially in diabetics, new vessels or alternate channels form, which is called angiogenesis, and this averts the gangrene. In fact in many patients the main artery may be totally blocked without any gangrene of the affected part. Because the blocks in such cases are widespread, this is also the reason why peripheral bypass and angioplasty is normally not recommended in diabetics, and the reason for lack of limb salvage after these procedures.
Lack of blood supply can also occur due to infection, which causes blockage of local blood vessels and tissue death and gangrene. This is the so called WET GANGRENE.
In diabetics however, because of the disease, the gangrene which takes place is many times a mixed one , as apart from the infection, almost all diabetics have a reduced blood supply.
So treatment of the gangrene and the diabetic foot ulcer entails taking care of and treating all such factors simultaneously to achieve healing and closure.