The radius is longer of the two bones that make up the human antebrachium or forearm. At the proximal end, the radius articulates with the capitulum of the humerus and the radial notch of the ulna to form the elbow joint. At the distal end, the radius articulates with the ulna via the ulnar notch, forming the distal radioulnar joint. Distally, the radius also attaches to the carpal wrist bones (scaphoid and lunate) to form the radiocarpal joint.
The radius has a nail-shaped head, and a short neck that extends to the oval-shaped prominence termed the radial tuberosity. The radial tuberosity attaches to the biceps brachii muscle. The radial shaft is slightly curved and has an interosseous membrane connecting it to the ulna along its entire length. The shaft also consists of multiple attachment sites for the muscles, including pronator teres, pronator quadratus, supinator, and other hand muscles that help in the pronation, supination, flexing, and extension movements of the forearm bone.
During pronation, the radial head crosses over the ulna, so the palm faces posteriorly, while a reversal of this movement allows the palms to supinate and face anteriorly. An annular ligament surrounding the radial head stabilizes the head to the ulnar notch.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 8.2: Bones of the Upper Limb.
