Articular disc of distal radio-ulnar joint

At a glance

English

Articular disc of distal radio-ulnar joint

Latin (TA2)

Discus articulationis radioulnaris distalis

System

Cartilage

Region

Upper limb

Side

Paired, left and right

About the articular disc of distal radio-ulnar joint

The articular disc of the distal radio-ulnar joint, often called the triangular fibrocartilage, lies across the lower end of the ulna at the wrist. It is a firm triangular plate. Its base is attached to the sharp lower edge of the ulnar notch of the radius, and its apex is fixed to the base of the ulnar styloid process and the small depression beside it, the fovea. It is thin in the middle and thicker along its front and back edges, which blend with the palmar and dorsal radio-ulnar ligaments.

The disc has two working faces. Its upper surface is smooth and faces the head of the ulna, forming the floor of the distal radio-ulnar joint, a pivot joint in which the radius turns around the ulna. Its lower surface faces the lunate and triquetrum and, together with the distal end of the radius, forms the proximal surface of the wrist (radiocarpal) joint. The wrist is an ellipsoid (condyloid) joint between this combined surface above and the scaphoid, lunate and triquetrum below. Because of the disc the ulna itself does not touch the carpal bones, and the cavity of the radio-ulnar joint is normally separate from that of the wrist.

The disc is the central part of the triangular fibrocartilage complex, which also includes the radio-ulnar ligaments, a meniscus-like fold, the ulnar collateral ligament and the sheath of extensor carpi ulnaris. This complex holds the lower ends of the radius and ulna together while the radius swings around the ulna in pronation and supination, and it cushions load passing from the hand to the ulna. Its edges have a blood supply from the anterior and posterior interosseous and ulnar arteries, but its central part does not, so central tears heal poorly.

Tears of the disc follow falls on the outstretched hand or forced twisting, or develop with wear as it thins with age, especially when the ulna is relatively long. They cause pain on the little-finger side of the wrist, clicking and weakness of grip, and are shown by MRI or arthroscopy. Peripheral tears can be repaired; central degenerative tears are usually trimmed.

Attachments and function

Attaches from

Its base is attached to the inferior margin of the ulnar notch of the radius.

Attaches to

Its apex is attached to the fovea at the base of the ulnar styloid process; its margins blend with the palmar and dorsal radio-ulnar ligaments.

Function

Binds the distal ends of radius and ulna, separates the distal radio-ulnar joint from the wrist joint, and transmits and cushions load from the carpus to the ulna.

Nerve supply

Branches of the posterior interosseous, anterior interosseous and ulnar nerves supply its periphery.

Blood supply

The periphery receives branches of the ulnar artery and the anterior and posterior interosseous arteries; the centre is avascular.