One of the main causes of foot and leg amputations in diabetics is a condition called diabetic neuropathy.
Patients with neuropathy often have decreased sensation in their lower extremities and therefore cannot feel injuries to their feet. Consequently, if a diabetic has a blister or cut on the foot, it can develop into an infected wound that soon spirals out of control. This rapid onset of infection can then spread to the surrounding area, and may progress to the underlying bone.
I advise all diabetics to establish a relationship with a podiatrist, and to have periodic foot checkups. Prevention is the key to good foot health.