Neuropathic (Charcot) Arthropathy

Neuropathic (Charcot) Arthropathy is an aggressive, deforming arthritis that results from a combination of repetitive trauma, peripheral neuropathy with impaired perception of injury, and ischemia with poor healing.

The classic radiographic findings of neuropathic arthropathy include a mixed pattern of proliferation and erosion that can be forced to start with the letter D. Starting from the joint and working our way into the bone, these are:

• Dislocation
• Debris in the joint space
• Destruction of articular surfaces
• Dense subchondral bone
• Deformity of the bones

Causes of neuropathic arthropathy include:

• Diabetes mellitus: Most common cause. Commonly affects the forefoot, midfoot and ankle. The image above shows a patient with diabetes mellitus. Typical findings include, calcaneal fragmentation with fracture planes extending into the subtalar joints, talar disruption, and dorsolateral displacement of the metatarsal bones. The metatarsal heads may be flattened or fragmented as seen aboveo (particularly at the 2nd metatarsal). There may also be osseous resorption of the metatarsal heads. The metatarsals and proximal phalanges may be tapered with "pencil-pointing" of the phalangeal and metatarsal shafts and widening of the bases of the proximal phalanges to form a cup ("intrusion," "mortar and pestle," "bulbous," "pencil and cup," or "balancing pagoda.")
• Alcoholism: Neuropathic arthropathy is infrequent, despite the presence of peripheral neuropathy in close to 30% of alcoholics. Findings and pattern of involvement is similar to those of diabetic patients.
• Syringomyelia: Neuropathic arthropathy occurs in about 25% of patients. The upper extremity is affected in 80%, with the shoulder being the most common site. Pseudosurgical appearance of the humeral head is characteristic. The spine is also commonly affected, with early findings similar to those seen in spondylosis.
• Tabes dorsalis: Charcot's original description of neuropathic arthropathy was mainly in patients with tabes dorsalis. Predilection is for the spine (especially lumbar) and lower limbs.
• Amyloidosis: Neuropathy may be seen in certain forms of amyloidosis, but neuropathic arthropathy is not common in these patients. The knee and ankle are most commonly affected in such patients.
• Myelomeningocoele: Ankle and intertarsal joints more commonly affected.

A diagnostic dilemma is differentiating simple neuropathic osteoarthropathy from superimposed osteomyelitis. MRI findings that help in this regard are sinus tract formation, replacement of soft tissue fat, fluid collections and extensive marrow abnormality support superimposed infection. If a prior MRI us available, progression of bone erosions, loss of subchondral cysts, increased marrow hyperintensity and enhancement of the articular surface support superimposed infection.

References

• Atalar AC, Sungur M, Demirhan M, Ozger H. Neuropathic arthropathy of the shoulder associated with syringomyelia: a report of six cases. Acta Orthop Traumatol Turc. 2010;44(4):328-36..
• Resnick D. Chapter 72: Neuropathic osteoarthropathy. in Diagnosis of Bone and Joint Disorders (4th ed). Saunders (2002): pp 3564-3595.
• Tan PL, Teh J. MRI of the diabetic foot: differentiation of infection from neuropathic change. Br J Radiol. 2007 Nov;80(959):939-48.