Triquetral bone

The triquetral bone (also called triquetrum bone, cuneiform bone, pyramidal bone, cubital bone, three-cornered bone, and triangular bone) is located in the wrist on the medial side of the proximal row of the carpus between the lunate and pisiform bones. It is on the ulnar side of the hand, but does not articulate with the ulna. It connects with the pisiform, hamate, and lunate bones. It is the 3rd most commonly fractured carpal bone.

The triangular bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone. It is situated at the upper and ulnar side of the carpus. To facilitate its palpation in an exam, the hand must be radially deviated so that the triquetrium moves out from under the ulnar styloid process. The triquetrum may be difficult to find, since it also lies under the pisiform.

The etymology derives from the Latin triquetrus which means "three-cornered."

Surfaces
The superior surface presents a medial, rough, non-articular portion, and a lateral convex articular portion which articulates with the triangular articular disk of the wrist.

The inferior surface, directed lateralward, is concave, sinuously curved, and smooth for articulation with the hamate. The dorsal surface is rough for the attachment of ligaments.

The volar surface presents, on its medial part, an oval facet, for articulation with the pisiform; its lateral part is rough for ligamentous attachment.

The lateral surface, the base of the pyramid, is marked by a flat, quadrilateral facet, for articulation with the lunate.

The medial surface, the summit of the pyramid, is pointed and roughened, for the attachment of the ulnar collateral ligament of the wrist.

Triquetral Bone in Culture
The triquetral bone (most commonly called "triquetrum") was discussed on air during an episode of The Colbert Report. During a guest appearance of his orthopedic surgeon, a CT scan of Stephen Colbert's left wrist was flashed on screen and demonstrated a chip fracture of his triquetrum. Colbert replied, "That's exactly what it felt like."

Additional images
Os triquetrum Os triquetrum 三角骨 Kość trójgraniasta Osso piramidal Trojhranná kosť