Charcot Foot

Jean-Martin Charcot (1825-1893) was the first to describe the disintegration of ligaments and joint surfaces (Charcot disease, or Charcot joint) caused by disease or injury. Charcot foot is the term given to neurogenic arthropathy that affects the joints in the foot. Neurogenic arthropathy is a rapidly progressive degenerative arthritis that results from damaged nerves (neuropathy).
In Charcot foot, pain perception and the ability to sense the position of the joints in the foot are severely impaired or lost, and muscles lose their ability to support the joint(s) properly. Loss of these motor and sensory nerve functions allow minor traumas such as sprains and stress fractures to go undetected and untreated, leading to ligament laxity (slackness), joint dislocation, bone erosion, cartilage damage, and deformity of the foot. The bones most often affected are the metatarsals and the tarsals, located in the forefoot and midfoot, respectively.

Anatomy

Nerves
Motor nerves carry signals from the brain to the muscles to allow gross and fine movements, such as walking and holding a pen. Sensory nerves carry information about shape, movement, temperature, texture, and pain to the brain. Loss of motor nerve fibers can cause muscular weakness. Loss of sensory nerve fibers can cause loss of feeling.
Autonomic nerves control unconscious functions such as heart rate, digestion, breathing, and so on. Loss of autonomic nerve fibers may cause increased blood flow to joints, which increases bone resorption (link to osteoporosis), or loss of bone, and the risk for fractures.

The Foot

The bones most often affected in Charcot foot are the tarsals and metatarsals.
Incidence and Prevalence
Charcot foot occurs most often in people with diabetes mellitus. According to the American Diabetes Association, 60%-70% of people with diabetes develop peripheral nerve damage that can lead to Charcot foot. Onset occurs after the patient has been diabetic for 15 to 20 years, usually at the age of 50 or older. The disorder occurs at the same rate in men and women.

Risk Factors

Diabetes mellitus and preexisting neuropathy are the primary risk factors.

Causes

Chronic hyperglycemia (high levels of glucose in the blood), the hallmark of diabetes mellitus, is believed to trigger the development of neuropathy, which, over time, may proceed to Charcot foot. Precisely how this causes nerve cell deterioration is unknown.

Symptoms

While peripheral neuropathy develops over decades, the progression of Charcot foot (ligament tears, small fractures, subluxation, dislocation, deformity) can occur in a matter of weeks or months. A minor trauma, such as twisting the foot, can initiate the process. Increased bone resorption makes the joints in the foot susceptible to small fractures.

Because of the loss of pain perception and the loss of the sense of position of the foot, joints receive repeated injuries, such as torn ligaments and bone fractures.

Early signs that may present soon after injury include the following:

Heat
Insensitivity in the foot
Redness
Strong pulse
Swelling of the foot and ankle
The early stage of Charcot foot may manifest these symptoms:
Dislocation of the joint
Instability of the joint
Subluxation (misalignment of the bones that form a joint)
Swelling
After an injury, the synovial fluid that leaks out of the joint capsule may produce swelling.
Muscle weakness and slack ligaments caused by nerve damage cause instability of the joint and subsequent misalignment (called subluxation) and/or dislocation.

Subluxation initiates the process of degenerative joint disease (arthropathy). The ends of misaligned bones grind against each other and fragments of bone and cartilage fall into the joint and often produce audible crepitus, a coarse grating sound, when the joint is moved. The physician may be able to feel these fragments in the joint.

Deformity of the foot that occurs in advanced disease is caused not only by joint displacement and/or dislocation but also by osteophytes and fractures. Large bony overgrowths, or osteophytes, develop as the body replaces lost bone with new bone and may protrude from the top of the foot. Fractures may cause the tarsal bones to collapse and outward bowing of the arch, or "rocker foot."

Complications

Calluses and ulcers may form when bony protrusions rub inside the shoes. Infected pressure ulcers and osteomyelitis (inflammation of the bone caused by infection) may develop. Septic arthritis may manifest with malaise and fever. Characteristics of septic arthritis include inflammation of synovial membranes and infected synovial fluid escaping from the joint capsule into the joint.

Compression of blood vessels and nerves are caused by disorganization of the joint and may not produce symptoms due to loss of feeling in the foot.