Histochemistry of abductor hallucis muscle in children with idiopathic clubfoot and in controls.

The histochemical composition of the abductor hallucis (AH) muscle was investigated in 39 children with idiopathic clubfoot (CF), aged 0-11 years, and in 42 controls. In the youngest group of patients (0-2 years) the percentage of type 1 (slow twitch, tonic) fibers was significantly higher than in controls. In older groups, there was no difference between patients and controls. The relative predominance of type 1 fibers could be due to immobilization, passive shortening or stretching, or primary overactivity of this muscle in CF promoted by an unknown neural factor. None of these interpretations could be proven.