Imaging of Charcot foot

The onset of a Charcot foot ist a feared complication of a long lasting diabetes mellitus. A peripheral neuropathy and continuous weight bearing of the foot subsequent to repeated traumas depict the conditions. There exist three types of a Charcot foot, an atrophic, a hypertophic and a mixed type. In early stages a differentiation from osteoarthritis is difficult. Subluxation or luxation within the Lisfranc's joint is typical. The joints of the foot could rapidly and extensively be destroyed or may present the morphology of a 'superosteoarthritis'. Often, soft tissue infections or osteomyelitis evolve from ulcers of the skin as entry points. Diagnosis of osteomyelitis necessitate MR imaging as plain radiography offers only low sensitivity for detection of an osteomyelitis. The existence of periosteal reactions is not a proof for osteomyelitis. Bone marrow edema and soft tissue edema also appear in a non infected Charcot foot. The range of soft tissue infections goes from cellulitis over phlegmon to abscesses. The ghost sign is the most suitable diagnostic criterion for osteomyelitis. In addition, the penumbra sign or the existence of a sinus tract between a skin ulcer and the affected bone may be helpful. (orig.)