Many different diseases can cause the arthropathy. The leading cause in Western countries is diabetic neuropathy, and neuropathic arthropathy occurs in approximately 7.5% of diabetic patients but more frequently in those with significant clinical evidence of neuropathy. Charcot joints are also associated with syringomyelia, tabes dorsalis, myelomeningocele, and a group of miscellaneous neurologic disorders, including spina bifida and Charcot-Marie-Tooth disease among others. The loss of proprioception and pain sensation leads to the relaxation of the ligaments and other structures that support the joint. Dysregulation of blood flow to the joint due to abnormalities in the autonomic nervous system contribute to an imbalance between bone formation and resorption. Joint instability results, and, later, injuries related to either daily activities or the neurologic dysfunctions initiate the destruction of bone and cartilage. These changes are similar to those seen in advanced osteoarthritis.

The joints affected depend on the primary neurologic disorder. Diabetic neuropathy most frequently involves the tarsal, metatarsal, and ankle joints. In tabes dorsalis the knee, hip, ankle, and lower thoracic and lumbar vertebrae are most often affected. In syringomyelia, the elbow or shoulder is the site of involvement.

Clinical Manifestations. Patients most often present with a monarthritis. Insidious swelling or instability (or both) of the involved joint is usually the first abnormality noted, followed by effusion and joint destruction. Pain, however, is relatively mild and less than expected based on examination and radiographic findings. Physical examination reveals an enlarged, hypermobile, and slightly tender joint with a large effusion. The effusion and enlargement gradually increase. Late in the disease process, the prominent sign is crepitation, caused by the extensive destruction of cartilage and bone and the accumulation of intra-articular loose bodies. In diabetic neuropathy, the foot widens and the ankle becomes irregularly swollen. Patients may develop spontaneous fractures or dislocations. In the diabetic foot, the toes, midfoot, tarsometatarsal joints, ankle, and calcaneus can be involved. Skin ulcers overlying the areas of joint involvement may occur. Synovial fluid is typically noninflammatory and may be hemorrhagic.

Radiographic Findings. At first, radiographs may appear basically normal, revealing only joint effusion. Often, soft tissue swelling is massive. Later, loss of cartilage and resorption and fragmentation of bone create a radiographic appearance of numerous loose bodies, bony displacement, and unusually shaped osteophytes at the joint margins. The joint looks like a “bag of bones.” MRI may be helpful in diagnosis in the early stages, confirming syringomyelia and differentiating osteomyelitis from neuropathic joint changes.

Treatment. Prompt attention to minor trauma is important to prevent progressive of joint disease. Supportive measures such as the use of braces, splints, orthotics, or casts to stabilize the joint and crutches or a walker may help to decrease the disability. Physical therapy to promote strengthening and occupational therapy to assist in skills of activities of daily living should be considered. Bisphosphonates may be of value in retarding damage in the early phases of Charcot arthropathy. Arthrodesis (joint fusion) may be useful in the foot, ankle, knee, or spine after healing of the active phase. Arthroplasty (total joint replacement) has generally been less effective.