Ulcers are skin wounds that are slow to heal. In the foot, as prominent metatarsal heads on the plantar (bottom of the foot)are subjected to increased pressure, the skin begins to become callused. When subjected to shearing forces, there is a separation between the layers on this callused skin, which fills with fluid and becomes contaminated and infected. The result is a foot ulcer.

Ulcers are classified in four stages, according to how deeply they penetrate the layers of skin they have broken through.

The four stages of ulcers are:

• Stage 1—Characterized by reddening wounds over bony areas. The redness on the skin does not go away when pressure is relieved.
• Stage 2—Characterized by blisters, peeling, or cracked skin. There is a partial thickness skin loss involving the top two layers of the skin.
• Stage 3—Characterized by broken skin and sometimes bloody drainage. There is a full thickness skin loss involving subcutaneous tissue (the tissue between the skin and the muscle.)
• Stage 4—Characterized by breaks in the skin involving skin, muscle, tendon, and bone and are often associated with a bone infection (osteomyelitis).

The are also four major cause of foot ulcers:

• Neuropathic—Related to the nerves and characterized by a loss of sensation in the feet.
• Arterial—Related to poor blood circulation to the lower extremity. This type of ulcer can be very painful and is usually found on the tips of toes, lower legs, ankle, heel, and top of the foot. It can very easily become infected.
• Venous—Related to compromised veins. These ulcers are often seen around the inside of the ankle and are slow to heal.
• Decubitus—Derived from excessive and prolonged pressure on one area of the foot. The most common type of decubitus ulcer of the feet is bed sores on the backs of the heels of people confined to bed for long periods of time.

Foot ulcers are a common problem for diabetics. Contact casts are sometimes applied to the diabetic foot to relieve the bony prominent areas of pressure, allowing ulcers to heal.