During standing and walking, the soles of the feet are in contact with the ground. This relatively small area of contact surface tells the body about its position, as well as detailed information about the terrain being traversed. The tough plantar epidermis and dermis are thick and able to withstand the numerous forces that a moving body produces. The primary "shock absorber" of the sole of the foot is a modified layer of fat. The blood and lymphatic vessels of the foot are under high hydrostatic pressure. As a consequence, edema easily results from injury and can retard healing. Except for the arch area, the epidermis and dermis of the soles are quite thick. Despite this, the foot is quite sensitive to two-point discrimination and pressure. The heel has an 18-mm-thick modified pad of fat separated into chambers by fibrous septae. There is an additional broad internal fibrous arch, called the inner cup ligament, aiding to maintain the shape of the heel. The skin of the sole readily hypertrophies and can become quite thickened, especially in people who walk barefooted.
The dorsal aspect of the foot provides little protection to underlying tendons, nerves, and blood vessels. The dorsum of the foot is particularly vulnerable to work-related injuries such as when heavy objects are dropped on the foot.
The pattern of pedal tendons roughly approximates that of the hand. One important location is just posterior to the lateral malleolus, where the peroneus longus tendon runs.
The structural design of the foot severely limits exploration of wounds to the plantar surface. The dense fibrous fatty tissue of the ball and heel makes exploration and visualization nearly impossible in the emergency department (ED), and the underlying structures are easily damaged. However, lacerations to the arch, although more uncommon, are more readily explored.
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