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What Causes a Foot Ulcer?

Patients with diabetes are prone to major foot problems. This is because many of the underlying effects of diabetes, including neuropathy, vascular disease, and diminished response to infection, affect the foot.

As a result of the neuropathy, the foot can develop an ulcer. This happens for two reasons. The first is that the neuropathy causes paralysis of small muscles in the foot, which results in clawing of the toes. Clawing of the toes causes prominence of the metatarsal heads (bones closest to the toe) on the bottom of the foot as well as the knuckles on the dorsum (top) of the foot.

Neuropathy also lessens sensation in your feet. As the prominent metatarsal heads on the plantar (bottom) of the foot are subjected to increased pressure, the skin will begin to enlarge and become callused. Calluses can lead to a separation between the layers of the skin. The layers can fill with fluid, which can then become contaminated and infected. The pressure also can cause the skin to break down in these areas, causing a foot ulcer. Once the initial breakdown and contamination occurs, the foot may develop more significant problems because of infection.

The second way an ulcer can form is through the process known as the "Charcot foot." In this situation, because of the neuropathy, bones in the foot that are subjected to trauma will fracture and collapse. When subjected to the stresses of movement after surgery, the foot will become deformed. Often, this deformity is in the shape of a rocker, causing prominence of bone in the middle portion of the foot. The prominence in the middle portion of the bottom of the foot is then at risk of ulceration due to the same mechanism described above.

What Is a Total Contact Cast?

The total contact cast is a specific casting technique that is used to heal diabetic foot ulcers and to protect the foot during the early vulnerable phases of Charcot fracture dislocations. The cast is used to heal diabetic foot ulcers by distributing weight along the entire sole of the foot. The cast makes close contact with the exact contours of the foot; hence the name, "total contact cast."

The total contact cast relieves the pressure on the prominent areas of the foot, which allows the ulcers to heal. The cast should applied in such a way that the patient can remain mobile while the ulcer heals. The cast is molded to the contours of the foot from the back of the heel through the arch region, in the region of the metatarsals, around the metatarsals, and even to the toes. The pressure, which has been concentrated on the bony prominence, is now distributed over the entire sole of the foot.

For the Charcot foot, the total contact cast is used in two ways. In the initial treatment of the Charcot foot when the breakdown is occurring and the foot is quite swollen and reactive, the cast is applied to control the movement of the foot and support its contours. In this instance, the patient is often asked not to put weight on the foot. If the foot has already become deformed and ulceration has occurred, the cast controls movement and supports the foot that has become deformed due to paralysis of the small muscles.

Photo of a total contact cast


The total contact cast is applied in a different fashion than normal casts. It is common to have the patient lie on his or her stomach on the casting table with the leg pointed straight up. The ankle should be bent to a neutral position, if possible, to give the doctor applying the cast access to the sole of the foot. The doctor will apply a thin dressing over the ulcer, then a thin layer of stockinette. The doctor applies protective cast padding between the toes and very thinly up the leg. Secondary foam padding is applied over the toes at the bony prominences on the inner and outer side of the ankle and often times on the sides of the cast and the front of the shin.

Once this has been accomplished, the plaster undercoat is applied very carefully and smoothly to the foot and leg, completely encasing the toes and going up the leg. The sole of the cast is carefully molded to the contours of the sole of the foot. These valleys are then filled in with plaster of Paris or other material so that the sole of the cast is flat. Often, the cast is reinforced by fiberglass and a special curved or rocker-bottom sole is applied to relieve the stresses of walking.

The cast is then changed weekly or every other week depending on the physician, their experience with each individual patient, and the amount of swelling in the leg. Casting is continued until the ulcer is healed, and the foot is ready for appropriate shoes and orthotics. In the case of Charcot foot, casting is continued until the patient's fractures heal and the foot no longer needs a cast for protection. Because of the prolonged need for immobilization, the physician may convert the treatment to a removable walking boot.

Risks and Complications

Patients with diabetes are at risk for developing sores or areas of irritation under the total contact cast. Before getting thet cast, the foot must be monitored carefully to make sure it has an adequate blood supply. The cast must be applied by someone who has experience with the applications and use of this cast. The cast must be changed at regular, short intervals of 1-2 weeks. When these guidelines are followed, the total contact cast is a very effective treatment for ulcers and Charcot foot problems.


Contributors/Reviewers: Glenn Shi, MD; Hui Zhang, MD

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