Summary: The fundamental pathology in rigid clubfoot appears to be a neuromuscular defect. In order to test this hypothesis, 90 muscle biopsies were obtained from the posteromedial, peroneal, and some intrinsic muscles at surgical correction of 13 clubfoot patients. All were examined ultrastructurally, and 48 biopsies in nine of these patients were studied using enzyme specific histochemical stains at the light microscopic level. Neuromuscular junctions were isolated in the latter group. Consistent ultrastructural abnormalities were observed in all specimens. Histochemistry revealed a dominant Type I fiber population and Type I fiber grouping. A correlated increase in Type I neuromuscular junctions occurred in these areas. Since these changes are recognized as being neurogenically determined, a neuromuscular abnormality may be significant in the etiology of clubfoot.
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