The lunate (os lunatum or semilunar) is one of the carpal bones and is a component of the proximal carpal row.
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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
- extrinsic ligaments
- palmar: radiolunotriquetral, radioscapholunate, ulnolunate ligaments
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
- bipartite lunatum 6
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
Ossification 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".
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