High Quality Content by WIKIPEDIA articles! Radial Aplasia is a congenital defect which affects the formation of the radius bone in the arm. The radius bone is the lateral bone which connects to the wirst via articulation with the carpal bones. A child born with radial aplasia has no radius bone in one or both of his or her arm(s). Radial Aplasia also affects the thumb to be either part formed or completely absent from the hand. Radial aplasia is connected with the condition VACTERL association.