Why would i need an amputation if i have diabetes and i have a foot ulcer?

Inadequate bloodflow: The main problem with diabetes & feet is that diabetes causes decreased blood flow in the distant parts of the body (e.g. Feet) leading to nerve starvation so that sensation decreases. Then a cut can go unnoticed and get infected spreading to the bone. Antibiotics can only help if it can be carried by the blood to the site. If not, the infection spreads. Amputation is the only option left then.

infection: Poor circulation is the primary reason diabetics need amputation. The next most common reason is a bone infection. This happens when a soft tissue infection has festered down into the bone. Antibiotics will help treat the infection, but surgery to scrape the bone is often required. If surgery can't erradicate all the infected bone sometimes amputation is done to prevent spread of infection.

Infection: Amputation is usually the result of tissue loss and/or bone infection of the underlying structures.

Infection / Flow: Uncontrolled infection and poor vascular blood flow are the most common reasons causing diabetic the need to have a foot amputation.