Aims: To review the clinical manifestations of the Charcot foot in diabetes mellitus, with particular reference to theories concerning aetiology.
Methods: Systematic review of the published literature, searching for the keywords 'Charcot', 'foot and diabetes' and 'neuropathy' on Medline, as well as by examination of the references in recent published reviews.
Conclusions: The Charcot foot of diabetes mellitus is a common problem, and yet is not widely recognized by non-specialists. The failure of professionals to identify the condition in its early phases is probably largely responsible for the gross deformity which follows continued weight-bearing. The condition is confined to those with severe peripheral neuropathy. It is thought to result from three factors: motor neuropathy leading to the development of abnormal forces within the foot, subsequent disorganization of the foot as a result of associated osteopenia and progressive destruction from continued weight-bearing, enabled by reduced pain sensation. The cause of the osteopenia is not known, but it is associated with increased bone blood flow, which may be mainly the result of loss of sympathetic innervation. The importance of increased limb blood flow in the pathogenesis of the Charcot foot has been recognized for over a century. Paradoxically, the increased flow is associated with evidence of macrovascular disease, in that the prevalence of vascular calcification of pedal vessels approaches 90%. After an interval of many months, the condition tends to evolve: the increased blood flow lessens, the osteopenia is reduced and the disorganized bones become sclerotic. This tendency for the condition to evolve remains unexplained, since it would not be expected if the condition was caused solely by progressive denervation. As a result, it is suggested that another factor may be involved in the pathogenesis of the Charcot foot: an abnormal vasomotor reflex, analogous to reflex sympathetic dystrophy, occurring against a background of severe peripheral neuropathy. The resolution of the condition occurs because it is the reflex component of the hyperaemia which proves self-limiting.