Radioulnar articulations

Introduction

As well as articulating independently with the humerus at the elbow joint, the radius and ulna also articulate with each other. They do so at their proximal and distal ends by a synovial joints of the pivot type, and by an interosseus membrane in the manner of a syndesmosis along their shafts. The predominant movement between the two bones is a rotation of the radius around the ulna, so that the two bones cross in space, producing pronation, and the reverse movement to bring the bones into parallel alignment producing supination. In pronation and supination the hand is carried with the rotation of the forearm, thereby giving a further axis of movement of the hand at the wrist. Indeed, in functional terms the combination of the forearm and the movements possible at the wrist means that the hand is united to the arm by a universal joint. The fact that the various axes about which movement occurs do not all pass through a common point, and that several joints are involved, gives stability to the hand when performing delicate tasks.

Without freely movable joints between the radius and ulna, perhaps the evolutionary development of the hand as a manipulative tool would not have been so successful. Nor perhaps would there have been so much development and enlargement of the brain, particularly of the cerebral cortex.