Charcot joint, also known as Charcot arthropathy, is the name given to the destruction of a joint resulting from overuse in the setting of sensory neuropathy.
The key point to recall is that regular use of any joint causes some damage. This is normal, but not the source of clinical problems, as the body senses that damage is occurring, the offending activity ** is stopped, and repair is allowed to take place.
If a patient lacks full sensation (especially pain sensation), they will not perceive that a joint is being overused and damaged by that overuse. In short: poor sensation leads to joint destruction. In the setting of sensory neuropathy, the ordinary feedback loop is broken: the pain signal one to stop inflicting the trauma (i.e., modulate activity) is lost and the harmful processes continue unabated.
Just as a lack of skin sensation may prevent a person from detecting ulceration and ultimately lead to a bedsore, a lack of joint sensation can lead to Charcot arthropathy.
Charcot arthropathy can be severely debilitating, not only because of the damage to the joint but also nearby soft tissues. This leads to a vicious cycle of ulceration, infection, and further bony deformities (Figure 1).
Figure 1: Example of soft tissue damage (left) and radiographic changes on x-ray (right) of Charcot joints.
Presentation, Diagnosis, and Etiology
A prototypical presentation for Charcot arthropathy is a diabetic patient, approximately 50 years old, with unilateral swelling, redness, and increased skin temperature around the mid-foot or ankle.
Of note, the presentation of Charcot joint is very similar to that of cellulitis or osteomyelitis (bone infection). Cellulitis and osteomyelitis are also common complications in diabetic patients and must be ruled out.
To help differentiate a Charcot joint from cellulitis, one may try to elevate the foot for several minutes. If erythema resolves, this favors Charcot joint to active infection; however it is possible for both to occur simultaneously. The possibility of concomitant processes – Charcot joint plus an active infection–must be considered, especially in a diabetic patient who is at risk for both of these pathologies.
In the 21st century, the main etiology of Charcot joint is diabetes. As diabetes progresses, it often leads to peripheral neuropathy. The loss of sensation promotes harmful overuse of the joint and subsequent deformity. This is why Charcot joint in a patient with diabetes is also referred to as “diabetic neuropathic arthropathy.”
Some clinicians also believe that the microvascular disease found in diabetic patients contributes to Charcot joint pathology due to alteration in bone metabolism. Historically, the main etiology of Charcot joint was syphilis. The association between Charcot joint and syphilis argues that lost sensation, and not microvascular disease, is the cause of arthropathy in Charcot, as tertiary syphilis is known to cause peripheral neuropathy but not microvascular disease.
RECAP: Charcot joint is damage to the joint caused by overuse that was not modulated because of neuropathy (often the result of diabetes). There is also, unfortunately, a cycle of ulceration, infection, and further bony deformities.
** note that the “offending activity” might be simply placing more weight on one region of the foot, not walking or running in general. Thus, modifying this activity need not require giving up walking or running entirely but merely altering the pattern of gait to shift weight a bit and place less pressure on the affected area. This shifting is often done subconsciously. Think about how painful it might be to stand completely motionless while waiting in line. The normal swaying and moving about while standing is done to relieve focal pressure on the joints.
Caption figure 2