Look for this and other related articles in Instructional Course Lectures, Volume 59, which will be published by the American Academy of Orthopaedic Surgeons in March 2010:"The Management of Complex Fractures and Fracture-Dislocations of the Hand," by Jesse Jupiter, MD, Hill Hastings, MD, and John T. Capo,MDForearm rotation is the most important contribution to the rotational mobility of the upper limb1. The two-bone unit with its proximal and distal radioulnar joints, and its rotational axis connecting the centers of the two, have been viewed as a single bicondylar joint. When combined with rotational motion of the shoulder, forearm rotation permits the hand to be positioned through an entire 360° arc of motion. With the shoulder fully abducted, nearly all of the rotational motion of the upper limb occurs through the forearm1. Activities such as accepting objects in the palm of the hand require nearly full forearm supination, while many other functional tasks require some degree of pronation. It has been suggested that, in addition to rotation along the axis of the forearm articulation, the distal aspect of the ulna moves in both adduction and abduction planes with forearm rotation, although some believe that this perceived motion may be due to axial rotation of the humerus2,3.