Muscle and tendon size relationships in a paralyzed chick embryo model of clubfoot.

Clubfoot is a birth defect that may be related to muscle weakness or imbalance. The purpose of this study was to examine the relationships among muscle and tendon size and embryonic motility in a paralyzed chick embryo model of clubfoot and arthrogryposis. Decamethonium bromide, a neuromuscular blocking agent, was administered to a series of embryos in five dosage groups, producing a cohort of embryos with various degrees of paralysis and atrophy of tendons and muscle. Embryonic movement frequency was monitored, and after death in late gestation, the cross-sectional areas of the calf musculature and the gastrocnemius tendon proximal to the ankle were measured histologically. Significant correlations were found between embryonic motility and both muscle (r2 = 0.52) and tendon (r2 = 0.77) areas. In addition, a significant correlation (r2 = 0.74) was found between muscle and tendon areas, suggesting that a measurement of one may be used to predict the other.