Necrosis is the unexpected premature death of the cells, not caused by the cells own internal systems. Diabetes, in particular type II diabetes arises due to poor diet and lack of exercise. The cells of the body become insulin resistant and are unable to obtain enough glucose.
The poor diet factor (high in fat) can cause Peripheral Arterial Disease (PAD) by atherosclerosis in the blood vessels of the lower limbs, particularly the legs. This restricts the flow of nutrient rich blood to the cells in the lower limbs meaning cells struggle to obtain the glucose, amino acids and oxygen to stay alive.
The lack of nutrients can go on to cause Peripheral Neuropathy (PD) or death of the neurones in the limbs. This intern means the sensation i the limbs s lost meaning an increase in minor trauma to the superficial (surface) structures (dermis/epidermis) and the greater chance of bacterial infection.
An increase in the presence of Oxygen free radicals in the blood also contributes to necrosis.