Pressure ulcers occur as a result of tissue damage produced by inadequate tissue perfusion. Forces caused by direct sustained pressure, repetitive moderate pressure and shear forces facilitate tissue ischemia and capillary occlusion

Heels are particularly susceptible to pressure injury. The bottom of the heel is well adapted to the forces created while standing and walking but the back of the heel is not.  There is only a thin layer of fat and skin covering the heel

When patients lie on their backs, the back of the heel is in contact with the bed or chair. The back of the heel does not have the fatty tissue to absorb the force of prolonged pressure or shear forces created during leg movement or transfers from a bed. In addition, the blood supply to the skin is poor and there is no muscle or tendon to cushion the bone and distribute pressure.  When the foot is resting with pressure on the back of the heel, all the pressure from the weight of the foot and lower leg is concentrated on the small area on the heel.  This pressure constricts the small blood vessels in the area starving the skin of nutrients causing the skin to breakdown and an ulcer to form