Bone · Hand

Lunate

Os lunatum

A crescent-shaped bone in the middle of the proximal row, sitting directly beneath the radius. Its name comes from the deep half-moon hollow on its lower surface, which caps the rounded head of the capitate like a socket. Almost every surface of it is articular cartilage, leaving very little bare bone for ligaments to grip, so it is held in position chiefly by the bones packed around it. Of all the carpals it is the one most completely surrounded by joint surfaces — the reason it is described as an intercalated bone, interposed between others with no muscle of its own.