The purpose of this study was to investigate the light microscopic structure of extrinsic foot muscles in talipes equinovarus (TEV) deformity that developed during intrauterine life due to high-level myelomeningocele. Ten feet of five fetal cadavers ranging in age from 18 to 20 weeks were dissected. Five feet had typical TEV deformity and the other five feet did not have any deformity (control group). Under light microscopic examination quantitative measurement of both muscle fiber sizes and fibrosis in the muscle tissue were performed to investigate the denervation muscle atrophy. Mean muscle fiber size of the TEV group was found to be significantly lower than that of the control group in all foot muscles except the gastrocnemius muscle. The proportion of fibrosis due to denervation atrophy was significantly higher in the TEV group than in the control group in all muscles. This situation was most evident in the peroneus longus muscle. It was concluded that muscular imbalance due to significant muscular atrophy might be the cause of TEV deformity that developed during intrauterine life due to high-level myelomeningocele. (c) 2004 Lippincott Williams & Wilkins.