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Plantar Ulceration

The development of plantar ulceration results from trauma, either a direct blunt force which causes a bruise beneath the skin or the pull on the subcutaneous tissues during walking or running.

When there is direct injury and bruising has occurred, there is swelling with scarring and destruction of the fibrofatty pad; the skin remains intact. The clotted blood and dead tissue liquefy and track to the soft tissue at the margin of the foot, producing a "necrosis blister" which will eventually break. The tract will heal if the limb is rested at this stage, but if infection occurs the overlying skin breaks down and ulceration results. When this heals, the scar tissue fixes the skin to deeper tissues or bone and a recurrent cycle is initiated.

The other pattern, trauma during walking, results from the movement of the skin backwards and forwards over the subcutaneous tissue. This is normal, and becomes painful if too much force is exerted.However, when there is anesthesia, or when the foot is scarred and the subcutaneous tissues are fixed, this movement is not possible and tissues break down and ulcerate (Fig. 34.9). The sites most commonly affected are over the metatarsal heads, the base of the fifth metatarsal, the base of the first proximal phalanx, and the calcaneum. Shoes compound the problem in an anesthetic foot because of blisters from friction or necrosis of the skin from pressure. Unfortunately, patients who have deformity or ulceration wear shoes to hide or "protect" their feet.

Long-standing plantar ulcers may undergo malignant change. Squamous cell carcinoma is most likely, but at least one case of malignant melanoma has been recorded. Distant metastases to the brain and chest and regional lymph node metastases have occurred. It is probable that malignant change occurs more often than is thought, because many cases are not recorded in the literature. It is difficult to distinguish between chronic infection, particularly with superimposed mycosis ("mossy foot"), and malignancy.

Further damage may be caused by absence of the stretch reflex and joint sensation. Ligaments may be torn and an ankle may be fractured without realizing there has been any injury if there is anesthesia, and this progresses to a neuropathic joint.

Fig. 34.9. A The soles of both feet of a leprosy sufferer. The trophic ulcer on the left foot has caused partial absorption of the bones with resultant deformity of the structure of the foot. This, in turn, leads to loss of normal balance of the foot. The gait changes, and the weight distribution of the foot, undergo modification; new pressure points may cause new ulcers. B At the heel of both hands, ulcers and scars may be noted due to pressure caused by the walking stick. C The loss of toes and foreshortening of the foot lead to poor stability. The patient uses a stick to balance himself, throwing extraordinary weight on the anesthetic hands. This causes rapid trophic changes and absorption of the fingers.

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Copyright: Palmer and Reeder