What Causes a Foot Ulcer?
Patients with diabetes are prone to major foot problems. This is because the foot expresses many of the underlying effects of diabetes, including neuropathy, vascular disease, and diminished response to infection.
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 causes diminished sensation. 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. The callused skin can be subjected to shear forces that cause 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 primary breakdown of the skin 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 subjected to trauma will fracture and collapse. The foot, when subjected to the stresses of movement after surgery, will become deformed. Often, this is in the shape of a rocker, causing prominence of bone in the middle portion of the foot rather than the metatarsal heads. The prominence in the middle portion of the bottom of the foot is then at risk of ulceration due to the same mechanism that has just been described.
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 plantar aspect (sole) of the foot. It is applied in such a way to intimately contact the exact contour of the foot; hence the name, "total contact cast."
The cast relieves the pressure on the prominent areas of the foot, permitting the ulcers to heal. The cast should applied in such a way that the patient can remain mobile during the treatment of the ulcer. 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 bear weight on the foot. In the second instance when the foot has already become deformed and ulceration has occurred, the principle using the cast is the same as described for the foot that has become deformed due to paralysis of the small muscles.
The total contact cast, when used for the described applications, is a very effective treatment. A prerequisite is that the foot must have an adequate blood supply, and therefore, the foot must be monitored quite carefully. 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 a week or two. The reason for this caution is that the diabetic who has insensitive feet runs the risk of having other sores or areas of irritation occur under the cast.
The 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. In this way the doctor applying the cast has access to the sole of the foot which is the all-important area. A thin dressing is applied over the ulcer. A thin layer of stockinette is applied and protective cast padding applied between the toes. Cast padding is applied very thinly up the limb and then secondary foam padding is applied over the toes at the bony prominences on the inner and outer side of the ankle and often times of 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. The cast is often at this point reinforced by fiberglass and a special curved or rocker-bottom sole is applied to relieve the stresses of walking if the patient is allowed to bear weight.
These casts are then changed weekly or every other week depending on the physician, his or her 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 the Charcot process, 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. The total contact casting technique is an effective treatment for ulcers and Charcot foot problems.
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