Charcot Foot
Charcot foot and ankle
is a progressive degenerative condition that affects the joints in the feet. It
is associated with nerve damage (neuropathy) that decreases the ability to
sense stimuli, including pain, and decreases muscular reflexes that control
movement. As a result, the joints in the feet are subjected to repeated
trauma and injury, causing progressive damage to the ligaments, cartilage,
and bones. Charcot foot affects the metatarsal, tarsometatarsal, and tarsal
joints, which are located in the forefoot and midfoot.
Incidence and Prevalence
Charcot foot and ankle occurs most often in people with diabetes mellitus. It
occurs at the same rate in men and women and develops in both feet in
approximately 20% of cases.
According to the American Diabetes Association, 60-70% of people with
diabetes develop peripheral nerve damage that can lead to Charcot foot and
about 0.5% of these patients develop the condition. In most cases, onset
occurs after the age of 50, and after the patient has had diabetes for 15 to
20 years.
Risk Factors and Causes
Diabetes mellitus and peripheral neuropathy are the primary risk factors for
Charcot foot. High levels of glucose in the blood (chronic hyperglycemia),
which is the hallmark of diabetes, can trigger neuropathy, which then may
proceed to Charcot foot. Precisely how this process occurs is unknown.
Signs and Symptoms
While peripheral neuropathy develops over decades, the progression of
Charcot foot can occur in a matter of weeks or months. Minor trauma, such
as twisting the foot, can initiate the process and the loss of pain perception
and the sense of foot position can result in repeated joint injuries.
Symptoms of Charcot foot include the following:
•
Dislocation of the joint
•
Heat
•
Insensitivity in the foot
•
Instability of the joint
•
Redness
•
Strong pulse
•
Swelling of the foot and ankle (caused by synovial fluid that
leaks out of the joint capsule)
•
Subluxation (misalignment of the bones that form a joint)
Nerve damage causes muscle weakness and slack ligaments, which result in
joint instability and subsequent 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 enter joint and often produce a coarse grating sound (audible
crepitus) when the joint is moved. The physician may be able to feel these
fragments in the joint.
Deformity of the foot, which occurs in advanced disease, is caused by joint
displacement and/or dislocation, bone overgrowths (osteophytes), and
fractures. Osteophytes may protrude from the top of the foot as the body
forms new bone to replaces bone loss. Fractures may cause the tarsal bones
to collapse, resulting in an outward bowing of the arch (called “rocker foot”).
Complications of Charcot foot include calluses and ulcers, which occur when
bony protrusions rub inside the shoes and may become infected. Bone
inflammation (osteomyelitis) and inflammation of the joint membranes
(septic arthritis) also may develop. Septic arthritis may manifest with
malaise and fever. Blood vessel and nerve compression may occur and often
do not cause symptoms due to the loss of sensation in the foot.
Diagnosis
Diagnosis is based on medical history (i.e., history of diabetes), symptoms,
imaging tests (e.g., x-rays, MRI), and laboratory tests. X-rays are used to
detect joint effusions, large osteophytes, fractures, bone fragments, and
joint misalignment and/or dislocation. Magnetic resonance imaging (MRI)
can be used to help differentiate between Charcot foot and osteomyelitis
(bone infection). Joint margins, which are clearly defined upon MRI in
Charcot foot, appear blurred in osteomyelitis. Laboratory tests include
drawing fluid from the joint (arthrocentesis) to detect bone and cartilage
fragments and blood, which may be present in some cases of Charcot foot.
Treatment
The goal of treatment is to stabilize the joint. In patients with diabetes,
restraining from placing weight on the foot for at least 2 to 6 months which
may help to prevent further damage. During this time, a total contact or
walking cast and crutches may be required to protect the foot.
Surgery may be necessary to treat severe deformities or recurring ulcers by
reshaping structures within the foot or removing bony protrusions that cause
ulcers. After surgery, the foot is monitored for signs of infection (e.g.,
redness, swelling, warmth).