Amputations in patients with diabetes happen primarily either from infection or in cases where they have recurrent or chronic ulcer that is at risk of causing infection.
In instances where infection reaches the bone underlying an ulceration, treatment with antibiotics is not guaranteed to treat the infection. It is very difficult for antibiotics to penetrate bone and therefore when antibiotics are recommended, it is through intravenous methods (a needle in the arm) and must continue for between 6-8 weeks of treatment. When a bone infection has been identified, depending upon the location within the foot, it may be recommended that amputation (or removal of that part of the foot) be performed. This is done to protect the rest of your body from becoming severely infected and to prevent a condition called sepsis, when the infection enters the blood stream and becomes life threatening.
There are some cases where recurring ulcerations on the feet can lead to amputation. This is more often seen in the tips of the toes. If ulcerations occur over and over, the risk of infection becomes higher and higher. There are some instances where ulcerations at the tips of toes are due primarily to a deformity in the toe that places increased pressure at the tip of the toe. Removal of a part of bone in the foot can sometimes also be performed and this may not require a visually appreciated loss of limb, but can help to prevent recurrent ulcerations if custom shoes and inserts have been shown to be ineffective. This is often seen for bones in the ball of the foot.