The radius is a bone in the forearm that extends from the elbow to the wrist. In a child born with a radial longitudinal deficiency (RDL), this bone is either absent or much shorter than it should be. This results in a misshapen forearm or wrist. Children with RDL also frequently have hypoplastic thumb. A hypoplastic thumb is usually smaller or weaker than an average thumb. It can affect any part of the arm—from the shoulder to the fingers.
Treatment—often surgical—is designed to create a straight, stable wrist and functional thumb. This condition is often associated with different congenital (at birth) syndromes where other parts of the body are affected as well.