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Other Terms: Intermediate carpal bone, Lunate bone, Semilunar bone, Os lunatum, Lunatum
This bone resembles a crescentic partial moon. It sits in the middle of the proximal row of carpal bones above the head or capitate bone. The capitate, third metacarpal, third row of phalanges, and this bone form the central axis of the hand. Its palmar and dorsal surfaces are approximately triangular and of a rough texture. These surfaces provide attachment for the ventral and dorsal radiocarpal ligaments. The remaining surfaces, proximal, distal, medial, and lateral are smooth articular surfaces for neighboring bones. The proximal aspect of the bone being convex while the distal aspect is concave.
Luna is the Latin term meaning moon. This bone is so named because of its crescentic moon-like shape. The semilunar bone is a synonymous name for this bone.
The lunate articulates with five bones: the radius, capitate, hamate, scaphoid, and triquetral. The proximal surface is smooth and convex for articulation with the distal radius and disc of the distal radioulnar joint. Its lateral surface is a concave semilunar facet for articulation with the scaphoid bone. The convexly arched distal surface forms three articular facets - a concave lateral facet for the head of the capitate, a central ridge-like articular surface for the hamate bone, and an oval medial facet for articulation with the triquetral bone.
The lunate ossifies from a single center that arises, on average, during the fourth year of life.