How does it happen?
Because the joint doesn’t have sensation, the person is often unaware of the damage that is happening. It may be a repeated microtrauma (an injury caused by repetitive stress), or a sprain or fracture that goes undetected due to the loss of sensation. The foot usually appears swollen, warm or red. Diagnosis and treatment are sometimes delayed as other diagnoses are explored.
How does Charcot joint progress?
From the initial event of being unable to feel, then a fracture or sprain, the foot begins to wear unevenly, and the bones may start to crumble. Along the way, the foot becomes misshapen and swollen. The classic deformity is a mid-foot collapse, which is known as a “rocker bottom” deformity due to the rounded shape of the bottom of the foot. If not treated early, weight-bearing on a deformed foot can lead to continued collapse and can also cause ulceration of the skin and an entry point for infection.
This can all feel painless to the individual, or only mildly painful, and they may be unaware of what is happening. Skin infection can progress to a bone infection. Again, this can go unnoticed as the foot may not hurt and the redness was already there from the initial Charcot joint. This leads to further destruction of the bones and can also spread to infect other places in the body.
The exact cause of a Charcot joint is not well understood. It is thought that microtrauma may lead to the release of inflammatory compounds that cause the bones to break down and then become weaker and collapse. Interestingly, it often occurs in people who have adequate blood supply to the legs and feet.