Radioulnar joints

The proximal radioulnar joint is a pivot joint: the circumference of the radial head rotates within an osseofibrous ring formed by the radial notch of the ulna and the annular ligament. It shares the elbow joint capsule. The distal radioulnar joint (DRUJ) is also a pivot joint: the ulnar notch of the radius rotates around the head of the ulna. It is stabilised by the triangular fibrocartilage complex (TFCC), whose articular disc binds the ulnar styloid to the radius and separates the DRUJ from the wrist joint.

The interosseous membrane is a fibrous sheet (syndesmosis) between the interosseous borders, its main fibres running obliquely downward and medially from radius to ulna, so that axial forces received by the radius from the hand are transferred to the ulna and thence to the humerus. It also provides attachment for deep forearm muscles and separates the anterior and posterior compartments.

In pronation the radius crosses over the ulna, carrying the hand so the palm faces posteriorly; in supination the bones lie parallel. The range is ≈160–180° (more with shoulder rotation). Supinators: biceps brachii (most powerful, with the elbow flexed) and supinator; pronators: pronator quadratus (prime mover) and pronator teres.