Lunate

The lunate (os lunatum or semilunar) is one of the carpal bones and is a component of the proximal carpal row.

Gross anatomy

Osteology

The lunate is crescent-shaped with a proximal convex articular facet and a distal concave articular facet. On the medial surface is a square-shaped facet and on the lateral surface is a semilunar facet. It is broader anteriorly than it is posteriorly. 

Articulations

• along with the scaphoid and triquetrum forms the distal articular surface of the radiocarpal joint
• intercarpal articulations
  • scaphoid (lateral)
  • capitate (distal)
  • triquetrum (medial)
  • hamate (distal and medial) - only in type II lunate
• articulates with the triangular fibrocartilage complex

Attachments

Musculotendinous

• nil

Ligamentous

• intrinsic ligaments
  • scapholunate ligament
  • lunotriquetral ligament
• extrinsic ligaments
  • palmar: radiolunotriquetral, radioscapholunate, ulnolunate ligaments

Blood supply

• arterial supply: branches from the dorsal radiocarpal arch and dorsal intercarpal arch supply the lunate via the dorsal and palmar surfaces (80%) or palmar surface only (20%) ²

Variant anatomy

• variation in articular facets (see: lunate morphology)
• lunotriquetral coalition
• associated accessory ossicles
  • os epilunate
  • os hypotriquetrum
  • os hypolunatum

Radiographic appearance

Plain radiograph

• frontal projection (neutral wrist position)
  • more than one-half should contact distal radial articular surface ³
  • should have a 'square shape' and the intercarpal joints should be uniformly 1-2 mm wide
  • forms part of the carpal arcs

Development

Ossification

Ossifcation typically begins at age four and is complete by age six or seven ². 

History and etymology

From the Latin "luna" meaning moon, referring to the crescent-moon shape of the lunate. It was first named the "lunatum" in 1653 by Lyser, and has also been termed the "lunare" or "semilunare".

Related pathology

• lunate dislocation
• perilunate dislocation
• Kienbock disease
• hamatolunate impingement syndrome
• scapholunate advanced collapse (SLAC wrist)
• scapholunate dissociation