Keep the Legs You Stand On by Dr. Mark Hinkes


Biomechanical Problems

There are multiple causes for development of diabetic foot ulcers related to biomechanical problems. These include bone, soft tissue, and nail deformities associated with faulty biomechanics, mechanical instability, connective tissue disease, muscle atrophy, fat pad loss, and calluses. Other reasons a person with diabetes might develop a foot ulcer is having a previous ulceration or amputation. Elevated blood glucose levels lead to the damage of connective tissue. This results in limited joint mobility, high peak pressures during gait, and loss of the normal heel and forefoot cushioning that can lead to the formation of ulcers. Ankle equinus, which causes a person to have a limited amount of heel contact, moves more pressure to the front of the foot. In an attempt to correct this kind of a problem, an Achilles-tendon lengthening surgical procedure can be done. This procedure reduces the amount of pressure across the mid-foot during walking. This procedure significantly reduces forefoot pressure as well and therefore reduces the risk for ulceration. The shortening of the calf muscle (gastroc-soleus equinus) causes an inability to move the toes upward, which is essential in the gait cycle of normal gait.

Bone deformities in the toes and feet can rub against your shoe and cause abnormal pressure. Ill-fitting footwear can also contribute to ulcer formation. When there is abnormal pressure against an underlying bony structure, your body tries to protect itself by forming a thickened skin or a natural protective pad commonly called a corn (located on the toes) or a callus (located on the bottom of the foot under the metatarsal bones). Patients with diabetes and sensory neuropathy may not feel the pressure caused by the thickened skin pushing against the bone. If that thick skin is not removed, you may develop an abscess under the corn or callus. The abscess can lead to an infection of the soft tissues called cellulitis. If the cellulitis is not treated promptly, it can cause a bone infection called osteomyelitis.


The next factor affecting the start of an ulcer is peripheral sensory neuropathy. PAD and PVD complicate ulcer healing but are not responsible for the creation of ulcers. Patients with diabetes having this condition or the loss of protective sensation in their feet from a variety of other reasons, such as cancer, medications, back problems and exposure to heavy metals may not feel pain when they injure themselves. Cuts, scratches, or lacerations that might go unnoticed in most patients can cause a catastrophe for the patient with diabetes or the at-risk patient. These wounds should sound big alarms because when things go wrong for patients with diabetes, they can go very wrong seemingly in the blink of an eye.

A variant of sensory neuropathy is the Charcot foot deformity. This problem is caused from increased blood flow with loss of bone (mineral) density and a propensity for micro fractures and destruction of the joints across the mid foot. With the bones in abnormal positions combined with faulty biomechanical function, ulcers are commonly seen on the bottom of the mid foot.


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Last Modified Date: August 07, 2013

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