Overview

The lunate lies between the scaphoid and triquetrum, its convex proximal surface articulating with the radius (lunate fossa) and the triangular fibrocartilage, and its concave distal surface cupping the head of the capitate (and sometimes the hamate). It is broader on its palmar than dorsal surface, which favours volar dislocation into the carpal tunnel under hyperextension forces.

It is bound to its neighbours by the scapholunate and lunotriquetral interosseous ligaments; disruption of the scapholunate ligament produces scapholunate dissociation (a widened gap — the "Terry Thomas sign" on X-ray). Its blood supply enters via both palmar and dorsal surfaces, but in some individuals only a single vessel supplies it, predisposing to avascular necrosis.

Location: Centre of the proximal carpal row, between scaphoid and triquetrum.

Anatomy

Articulations: Radius, scaphoid, triquetrum, capitate (± hamate); articular disc of the TFCC.
Ossification: Single centre ≈4 years.

Function

Central link between the radius and capitate
Transmits load across the wrist

Clinical significance

Lunate dislocation

The most commonly dislocated carpal; displaces anteriorly into the carpal tunnel causing acute median nerve compression. Lateral X-ray shows the "spilled teacup" sign.

Kienböck disease

Avascular necrosis of the lunate in young adults, associated with negative ulnar variance (short ulna) and repetitive loading; progressive collapse and wrist pain.

Test yourself

Which carpal bone is most commonly dislocated, and which structure may it compress?

Scaphoid — radial artery
Lunate — median nerve
Hamate — ulnar nerve
Pisiform — flexor carpi ulnaris

Answer: Lunate — median nerve

The lunate is the most commonly dislocated carpal; it typically displaces volarly into the carpal tunnel, acutely compressing the median nerve ("spilled teacup" sign on lateral X-ray).