The ulcer is often caused by the combination of, deformities and (minor) foot trauma & polyneuropathy that plays a central role in the majority of patients. Autonomic neuropathy can lead to dry fragile skin due to decreased sweat secretion and a warm foot with a tendency to edema. Sensory and motor neuropathy can lead to an insensitive foot with an abnormal gait, with increased pressure and/or shear and abnormal load when walking and standing. In response to the abnormal pressure and shear forces, the skin reacts with callus formation. However, an excessive amount of callus can lead to a further increase in pressure and shear, and callus is often a precursor to a foot ulcer. Due to loss of sensation, the patient continues to walk and the deeper tissues, between the skin and the underlying bone, are damaged without initially showing a few abnormalities. Eventually, a blister or skin defect develops, often preceded by subcutaneous bleeding. Blistering is mainly caused by local friction, in which, besides the biomechanical overload,also the time factor (duration of pressure and friction), the moisture of the skin and possibly underlying pathology play a role.In the experience of the guideline working group, a foot ulcer often starts as a blister, as an intracutaneous hemorrhage in callus or subcutaneous hemorrhage in callus, these abnormalities should, therefore, be considered an alarm signal. If no action is then taken with a present ulcer and the patient continues to walk on the foot - due to the reduced sensitivity - healing is not possible due to the continuous biomechanical overload. If an infection subsequently occurs, an amputation of (part of) the foot can sometimes be the only possible treatment.
Many patients with a foot ulcer also have standing abnormalities of the foot or exostoses. This puts an abnormal load on the skin and underlying tissues. In a follow-up study, 66% of all patients who developed a foot ulcer had foot defects, while these abnormalities were present in only 37% of patients who did not develop an ulcer. Claw or hammertoes can lead to increased plantar pressure at the heads of the metatarsal or interdigital pressure ulcers, ulcers on the dorsum of a toe, or ulcers on the medial side of the head of the first metatarsal in a hallux valgus. with these stand deviations, poorly fitting footwear will be the direct cause of the ulcer.
