The radius (radial bone) is one of two long bones that make up the forearm. Like the ulna, the radius also extends from the elbow to the wrist joint, lying on the lateral side of the forearm.

The radius articulates in several sites with adjacent bones. Proximally, the head of the radius articulates with the capitulum of the humerus, forming the humeroradial joint (part of the elbow joint). Additionally, the head of the radius also articulates with the radial notch of the ulna at the proximal radioulnar joint.

Distally, the ulnar notch of the radius forms a distal radioulnar joint with the head of the ulna. Finally, the distal end of the radius also articulates with the carpal bones (scaphoid bone and lunate bone) at the wrist joint. The diaphysis of the radius gives attachment to the interosseous membrane of the forearm.

The structures of the radius and their articulations with the humerus and ulna permit the forearm to do supination and pronation. The arrangement of the mentioned bones allows the radial head to rotate proximally, which causes anteromedial movement of the distal radius. The distal radius crosses over the distal end of the ulna, allowing the hand and wrist to pronate. An opposite movement is the supination.

As a long bone, the radius consists of the following three parts: proximal epiphysis, diaphysis, and distal epiphysis.

Note: 3D model displays the left radius.

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Radius