<unk>  is a spectrum of congenital abnormalities of the<unk>  varying from small defects to complete absence of the<unk> . It can be isolated, when only the<unk>  is affected, and in 60% of the cases it is associated with radial dysplasia (or radial club, radius dysplasia, longitudinal radial deficiency). Radial dysplasia is the condition in which the forearm bone and the soft tissues on the<unk>  side are underdeveloped or absent. In an embryo the upper extremities develop from week four of the gestation. During the fifth to eighth week the<unk>  will further develop. In this period something goes wrong with the growth of the<unk>  but the exact cause of<unk>  is unknown. One out of every 100,000 live births shows<unk> . In more than 50% of the cases both hands are affected, otherwise mainly the right hand is affected. About 86% of the children with hypoplastic<unk>  have associated abnormalities. Embryological hand development occurs simultaneously with growth and development of the cardiovascular, neurologic and hematopoietic systems.<unk>  has been described in 30 syndromes wherein those abnormalities have been seen. A syndrome is a combination of three or more abnormalities. Examples of syndromes with an hypoplastic<unk>  are Holt-Oram syndrome, VACTERL association and thrombocytopenia absent radius (TAR syndrome).
Thumb hypoplasia
Maxillary hypoplasia
Renal hypoplasia
Condylar hypoplasia
Radial aplasia
Hemifacial microsomia
Webbed neck
Ape hand deformity