The most common causes of lower extremity amputation are chronic ulcers (wounds), infections, and gangrene (peripheral artery disease).
A shallow diabetic foot ulcer can be a sign of a much larger problem.
Diabetes is known to cause many problems, including heart attack, stroke, kidney failure, blindness, and nerve dysfunction. Nerve dysfunction can sometimes be painful but is most often painless, simply leaving the feet numb. This numbness is dangerous because pain is necessary to protect the body from injury. When your feet are numb, you can cause damage by walking on an inflamed area, developing a callus unknowingly, or stepping on an object which causes direct injury. The injured area becomes inflamed and can turn into a deep blister, which eventually breaks open into a wound. A wound or ulcer is a break in the skin exposing the tissue under the skin (Figure 1). The ulcer can become infected (see Diabetic Foot Infection). Diabetes can lead to poor circulation (see Peripheral Artery Disease), which impairs the ability of the body to heal the wound. Ulcers can become deep with exposed tendon, muscle, or bone. The deeper a wound, the more complicated it is to heal.
Surrounding redness suggests this wound is infected.
A person with diabetes is predisposed to infection because diabetes suppresses the immune response. When there is an open ulcer, the bacteria – some of which normally live on the skin – gain access to the underlying tissue (Figure 2). The infection can spread rapidly, tracking along a tendon to enter compartments in the foot or leg.
Foot infections are classified as either limb-threatening or non-limb-threatening. Limb-threatening infections require hospitalization, IV antibiotics, and in many cases, surgery. These serious infections are sometimes life-threatening. Non-limb-threatening infections can usually be treated with oral antibiotics as an outpatient with careful follow-up. Many times infections can extend to the bone. If the bone becomes infected, it is called osteomyelitis. Osteomyelitis is not straightforward to diagnose. MRI or bone scans are often employed. In most cases the surgeon takes a culture of the bone to determine which bacteria is causing the infection. In certain cases, the bone has to be removed. A diabetic foot infection is a common pathway to amputation. Nearly 1 in 5 infections require some sort of amputation.
Diabetes alone and in combination with high blood pressure and high cholesterol causes damage to the lining of the arteries. The large arteries become narrowed or completely obstructed. This reduces the blood pressure and the amount of blood circulation in the extremities. The walls of the small arteries and capillaries become thickened so oxygen does not cross the wall as easily. If blood flow is reduced enough, gangrene can occur. Gangrene is black dead tissue and is either dry or wet. Wet gangrene is infected and requires emergency treatment. Gangrenous tissue cannot regenerate, but the surrounding margins might be saved.
An x-ray of a Charcot foot that is dislocated.
A Charcot foot (pronounced Shark-oh) is one characterized by destroyed bones and sometimes fractures and dislocations in the foot or ankle (Figure 3). Oftentimes, the arch of the foot collapses and there is a prominent bone felt on the bottom of the foot in the arch. This often leads to an ulcer on the bottom of the foot. Sometimes the bone will be infected if there is an ulcer that leads to it. Charcot foot is a condition that is commonly misdiagnosed as bone infection and may be unnecessarily amputated. It is important to have an expert in Charcot foot review the case prior to consenting to amputation because in the right hands, many cases are salvageable.
Pressure sores (ulcers) occur sometimes in those with diabetes, but can often happen without the presence of diabetes. The most common locations are on the backs of the heels and on the lower back above the buttocks. They occur when there is constant pressure on the skin from lying in one spot and not turning. Generally patients who acquire pressure sores are very sick or in a nursing home. This can complicate their treatment.