Scapholunate interosseous ligament

At a glance

English

Scapholunate interosseous ligament

Latin (TA2)

Ligamentum scapholunatum interosseum

System

Ligament

Region

Hand

Side

Paired, left and right

About the scapholunate interosseous ligament

The scapholunate interosseous ligament binds the facing surfaces of the scaphoid and lunate in the proximal row of the carpus. It is C-shaped: it covers the dorsal, proximal and palmar edges of the scapholunate joint, while the distal side of the joint stays open towards the midcarpal joint. Along this interval the ligament therefore separates the radiocarpal joint from the midcarpal joint.

It is described in three parts. The dorsal part is the thickest and strongest, made of short, transverse collagen fibres, and is the main restraint to separation and rotation between the two bones. The proximal part is thin, made of fibrocartilage, and is often perforated in older people. The palmar part is thinner than the dorsal, and its fibres run more obliquely, allowing the bones some rotation on each other. On the palmar side lie the strong radiocarpal ligaments; dorsally the ligament is supported by the dorsal intercarpal and dorsal radiocarpal ligaments.

Under load the scaphoid tends to flex while the lunate, tied to the triquetrum, tends to extend, and the ligament links the two so the row stays balanced. A tear, typically from a fall on the outstretched hand with the wrist extended, lets them separate: the scaphoid rotates into flexion and the lunate tilts into extension, the pattern called dorsal intercalated segment instability (DISI). Radiographs may show a widened scapholunate gap and a shortened scaphoid seen end-on as a ring. Pressing on the scaphoid tubercle while the wrist moves into radial deviation may make the scaphoid jump painfully over the back of the radius, the scaphoid shift test. Untreated, the abnormal loading leads to a set pattern of arthritis called scapholunate advanced collapse.

Attachments and function

Attaches from

Dorsal, proximal and palmar margins of the ulnar surface of the scaphoid.

Attaches to

Matching margins of the radial surface of the lunate.

Function

Binds scaphoid and lunate, couples their movement and stops them separating or rotating apart; it is the primary stabiliser of the scapholunate joint.

Nerve supply

Dorsally the posterior interosseous nerve; palmarly the anterior interosseous nerve.

Blood supply

Branches of the palmar and dorsal carpal arches that enter the carpal bones.