The lunate (os lunatum or semilunar) is one of the carpal bones and is a component of the proximal carpal row.
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.
- along with the scaphoid and triquetrum forms the distal articular surface of the radiocarpal joint
- intercarpal articulations
- articulates with the triangular fibrocartilage complex
- 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%)
- variation in articular facets (see: lunate morphology)
- lunotriquetral coalition
- associated accessory ossicles
- bipartite lunatum
- frontal projection (neutral wrist position)
- more than one-half should contact distal radial articular surface
- should have a 'square shape' and the intercarpal joints should be uniformly 1-2 mm wide
- forms part of the carpal arcs
Ossifcation typically begins at age four and is complete by age six or seven .
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".