Upper Extremity Embryology.

The development of the upper extremity begins early in embryogenesis, with the upper extremity fully formed by week 8 of gestation. This process relies on a complex cascade of molecular interactions-a single abnormality of which can result in congenital anomalies. Hand surgeons have the opportunity to significantly improve the quality of life of patients with congenital anomalies and require a thorough understanding of the underlying embryological processes resulting in these anomalies. This chapter provides an overview of the stages of upper extremity development, the molecular mechanisms of upper extremity embryogenesis, and the congenital anomalies that can result from abnormalities of various stages of this process.