What is a Charcot joint?
Charcot joint, also known as Charcot arthropathy, is the name given to the destruction of a joint resulting from lysis and fragmentation of the bone in the setting of neuropathy.
The prototypical patient with Charcot arthropathy is a person with poorly controlled diabetes associated with peripheral neuropathy and vascular disease. The patient will have swelling, redness, and increased skin temperature around the affected foot or ankle.
The pathogenesis of Charcot is not known with certainty. One theory is that the lack of sensation is responsible for the destruction of the joint. This is similar to the way the loss of skin sensation may lead to a bedsore: offending activities are not stopped because their damaging effects were not perceived.
A second theory is that neurovascular pathology leads to autonomic dysfunction and in turn increased blood flow. The greater blood flow to the bone results in bone resorption and fragmentation.
There may be yet an additional contribution from disease-related inflammatory cytokines that stimulate osteoclast activity and bone loss.
Charcot arthropathy can be severely debilitating, not only because of the damage to the joint but because of damage to the nearby soft tissues as well.
The joint destruction can result in abnormal foot geometry(for example, joint collapse). There may also be osteophytes (bone spurs). In turn, there may be focal pressure points that are prone to break down, leading to ulcers and infections.
Ulceration and infection set up a vicious cycle of additional bony destruction and skin breakdown, culminating in the need for an amputation (Figure 1 and Figure 2).
Of note, the presentation of Charcot joint is very similar to that of cellulitis or osteomyelitis (infection of the skin and bone, respectively). To help differentiate a Charcot joint from cellulitis, one may try to elevate the foot for several minutes. If erythema resolves, this favors Charcot and not infection as the diagnosis; however it is possible for both Charcot and infection to occur simultaneously.
Additional Points to Consider
Historically, the primary cause of Charcot joint was syphilis. Because tertiary syphilis is known to cause peripheral neuropathy but not microvascular disease, the association between syphilis and Charcot suggest that lost sensation – and not microvascular disease – is the cause of arthropathy. On the other hand, it is also known that syringomyelia from a Chiari malformation is associated with Charcot of the gleno-humeral joint, even though the shoulder is not subject to overuse damage like the foot. It is thus possible that both lost sensation and microvascular disease contribute.