The trapezium bone is an irregularly shaped carpal bone that is found at the radial border of the distal row. It sits at the base of the first metacarpal bone and is easily distinguished by its large saddle-shaped articular surface for the base of the first metacarpal bone. The trapezium is also known as the greater multangular bone.

The trapezium articulates with four bones - the first metacarpal bone and second metacarpal bone distally, scaphoid bone proximally, and trapezoid bone medially. Therefore, it has the following four articular surfaces:

Articular surface for first metacarpal - saddle-shaped;
Articular surface for second metacarpal - small and quadrilateral; directed distally and medially;
Articular surface for trapezoid - relatively shallow and concave;
Articular surface for scaphoid - shallow and quadrilateral.

The dorsal aspect of the bone is broad, elongated, roughened and relatively flat. It may have a shallow groove for the radial artery.

In contrast, the palmar aspect of the bone is narrower and more irregular. It has an elongated and raised bony prominence called the tubercle. Sometimes, the tubercle is also referred to as the crest. It is one of the sites to which the flexor retinaculum of the wrist attaches.

Medially to the tubercle is a groove that lodges the tendon of the flexor carpi radialis muscle. The transverse carpal ligament spans the groove, and its deep part separates the tendon of the mentioned muscle from the carpal tunnel. Therefore, although the tendon of the flexor carpi radialis is found below the transverse carpal ligament, it does not go through the carpal tunnel.

Additionally, the palmar surface of the trapezium also serves as an attachment site for the abductor pollicis brevis muscle, opponens pollicis muscle, and flexor pollicis brevis muscle.

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Trapezium