Charcot foot

CHARCOT neuroarthropathy is a relatively uncommon but serious complication of neuropathy. It was first recorded in a diabetes patient in 1936, and since then diabetes has grown to become the largest single cause of Charcot change in the developed world (leprosy in the undeveloped world).

But it is firmly held by those who regularly treat patients with Charcot feet that such changes are frequently overlooked, particularly by general practitioners and emergency departments, with potentially devastating effects. Most general practitioners might only need to recognise one active Charcot foot in a working lifetime but failure to diagnose and treat a Charcot joint can lead to significant deformity, disability and amputation, with the potential for successful and expensive claims for negligence.

Natural history

Eighty per cent of the patients who develop Charcot neuroarthropathy have a known duration of diabetes of over 10 years. The long duration of diabetes prior to the initiation of the Charcot process reflects the degree of neuropathy that is invariably present in these patients. The risk factors for Charcot neuroarthropathy are listed in the box on page 17. The blood supply to the Charcot foot is always good. It is assumed that autonomic neuropathy plays a part in the increased vascularity of bone and this increases osteoclastic activity, resulting in the destruction, fragmentation and remodelling of bone.

The initiating event of Charcot neuroarthropathy is often a seemingly trivial injury, which may result in a minor periarticular fracture or in a major fracture despite the inability of the patient to recall the injury in many cases. The patient may notice a change in the shape of the foot and others describe the sensation, or the sound, of the bones crunching as they walk. Following this there is a rapid onset of swelling, an increase in temperature in the foot and often an ache or discomfort. It is these processes which, if left untreated, lead to the characteristic patterns of deformity in the Charcot foot, including the collapse of the longitudinal and transverse arches resulting in the rocker bottom foot seen in cuneiform metatarsal Charcot neuroarthropathy or collapsed and distorted ankle joints in rear foot Charcot.

The natural history of Charcot neuroarthropathy passes from this acute phase of development through a stage of coalescence, in which the bone fragments are reabsorbed, the oedema lessens and the foot cools, into the stage of reconstruction, in which the final repair and regenerative modelling of bone takes place to leave a stable, chronic Charcot foot. The time course of these events is variable but intervention must be made in the earliest phase to prevent subsequent deformity, disability, ulceration and amputation.

Diagnosis

Charcot neuroarthropathy is frequently overlooked as the cause of a swollen, warm leg in a neuropathic patient with diabetes. If a history of injury, even a simple trip or toe-stubbing, is present then X-rays should be mandatory even if the other signs have not yet developed, and any fracture should be treated by casting. If the clinical signs of heat and swelling are present then normal X-rays should still be treated with caution. Precautionary casting or other immobilisation such as the air cast boot should be put in place until the X-ray is repeated or other investigations are performed. Isotope bone scans may help if the X-ray is normal.

Again, if reported as being consistent with osteomyelitis, when there is no history of open ulceration prior to the development of the heat and swelling, Charcot is still more likely. Computerised tomography and MRI scanning are reported to be better at discriminating between Charcot change and osteomyelitis but still have limited immediate availability in many hospitals.

Investigation for deep venous thrombosis and osteomyelitis often delay the start of appropriate therapy. In a diabetic patient with significant neuropathy, and with these signs and symptoms, it is better to assume that there is Charcot neuroarthropathy and treat accordingly, even if there is no clear history of injury. This is particularly true of the Charcot process in the ankle joint.

Treatment 

Once the diagnosis has been made then prompt and total immobilisation is the best way to reduce deformity. The duration of casting averages at least 18 weeks but the process can still restart after this period, requiring a return to cast. Patients, once removed from cast, need careful monitoring to ensure that any recurrence is treated promptly. Skin temperature differences between the active and unaffected foot remain the best marker of Charcot activity and are the most frequently used tool for monitoring resolution of the Charcot process.

If the patient is not immobilised, and even sometimes when they are, then the Charcot process proceeds to a destructive phase. The fragmentation and weakening of bones causes tendon and ligament insertions to detach. This leads to collapse of the normal foot architecture. In the ankle it also leads to loss of talar or calcaneal height leading to leg shortening and ankle instability.

Attempts to internally or externally fixate the fragmented bone are more common in North American practice. Fixation surgery for Charcot feet often has only a modest success in the acute stages and there are very few case series of any size, and virtually none with adequate controls, to suggest that ankle surgery is any better. In many cases surgery during the active phase of Charcot destruction can actually accelerate the process. Late surgery to correct mid-foot deformity can be considered as long as the foot is stable and uninfected. Once the ankle has become deformed and the ankle is unstable, particularly if ulceration is present, then primary amputation may be the best way to provide the patient with a functioning limb for walking, as attempts at orthopaedic surgical repair are often only partially successful or fail.

Early diagnosis and treatment can limit deformity but there is no attempt to address the underlying pathophysiology. With growing evidence that weakened bones and increased osteoclastic activity underpin the initiation and destructive phase of Charcot neuroarthropathy, treatment with bisphosphonates has been piloted in Manchester in the United Kingdom. A further randomised study and trials of oral bisphosphonates showed similar results with reductions in temperature, pain and swelling but the use of these therapies remains controversial.

Medicolegal pitfalls

The main pitfall in managing Charcot neuroarthropathy is the failure to consider it as a diagnosis in a susceptible and symptomatic diabetes patient. Whilst this is still a relatively frequent occurrence for non-specialists, at least on first presentation, once a patient has had negative Doppler scans and/or courses of antibiotics for presumed cellulitis with no improvement, if no thought is given to alternative diagnoses then a claim is likely to be successful. The size of that claim is likely to be determined by the degree of deformity and subsequent ulceration, and significantly larger if an amputation is required which is so often the case for untreated Charcot feet and ankles.

Summary

Charcot neuroarthropathy in diabetic patients is more common than generally recognised. Prompt action is required to prevent deformity and this is dependent upon early recognition and treatment. A neuropathic diabetic person with a hot swollen foot should be considered to have a Charcot joint until proven otherwise. Casting will curtail the active phase of bone destruction and bisphosphonates may also help but are not proven to do so. If possible, surgical correction of any deformity should be delayed until the active phase is over and the foot is in a stable healed state. Occasionally, when the ankle complex has been destroyed, amputation will provide a more functional lower limb for walking than leaving the ankle in place.

Risk Factors

The following are risk factors in the development of Charcot neuroarthropathy

• Duration of diabetes (usually greater than 10 years)
• Dense peripheral neuropathy
• Autonomic neuropathy
• Osteoporosis
• Other diabetes complications
• Transplant patients
• Young female patients with eating disorders (especially anorexia nervosa) leading to amenorrhoea

Dr Matthew Young is a consultant diabetologist at the Edinburgh Royal Infirmary Risk factors