[The Charcot joint].
Charcot foot in its original sense is equivalent to stage 4 of hereditary motor and sensory neuropathy (HMSN) which is known as Charcot-Marie-Tooth disease since 1886. This entity, which can be subdivided into 3 groups including subgroups, predominantly begins during childhood and progresses slowly. The first symptom, often unnoticed by the patient for a long period, is weakness of the intrinsic foot muscles with consecutive hammer-toe formation and mobile pes cavus. Progredient atrophy of the peroneal, extensor, tibialis posterior and finally triceps surae muscles leads to fixed pes cavus varus excavatus with severe varus deformity of the hindfoot, secondary varus position of the talus at the ankle level and subsequent arthrosis of the medial compartment. Permanent varus deformity of the ankle almost invariably leads to stress fractures of the malleoli because of repetitive microtrauma (stage 5 of HMSN). Early detection of the disease with nerve conduction studies at clinical suspicion allows tibialis posterior transfer, correctional osteotomy of the hindfoot or arthrodesis of Chopart's or Lisfranc's joint and can postpone or prevent the otherwise inevitable triple arthrodesis which has a less favorable long-term prognosis. At stage 4 (manifest Charcot foot) and stage 5 (neuropathic fracture of the ankle) a reorientating ankle arthrodesis is advocated, with additional subtalar pathology correctional double arthrodesis becomes necessary. In diabetic arthropathy of the ankle (Type IV according to Sanders and Frykberg), which is often referred to as "Charcot Ankle", tibiocalcanear arthrodesis is indicated. In case of supervening infection or extensive necrosis a modified Pirogoff amputation is carried out as a salvage procedure. Doubled periods of non weight-bearing, immobilization and brace protection of the ankle help to reduce the frequently observed implant failure in both forms of osteoarthropathy. In addition to stable implants retrograde calcaneotalotibial transfixation with a Steinmann pin may help to protect the achieved result despite prolonged bone consolidation.