Trapezium

The trapezium (also known as the greater multangular) is one of the eight carpal bones of the hand. It is the most lateral (radial) bone of the distal row, located between the scaphoid and the first metacarpal bone. It articulates with the scaphoid proximally, the trapezoid medially, and the thumb and index metacarpals distally. The trapezium and trapezoid are collectively known as the multangulars.

Gross anatomy

Osteology

The trapezium has six surfaces in total:

1. rough palmar surface which contains a medial groove and prominent tubercle
2. elongated rough dorsal surface
3. large lateral surface
4. concave medial surface
5. large dorsolateral sellar surface (i.e. saddle-shaped) ³ which projects distally between the thumb and index metacarpals, and also has a small distomedial facet articulating with the index metacarpal base
6. small concave proximal surface

Articulations

• articulates with the scaphoid at the midcarpal joint
• articulates with the trapezoid at its intercarpal joint
• articulates with the thumb metacarpal at the carpometacarpal joint of the thumb

Attachments

Musculotendinous

• superficial head of flexor pollicis brevis arises from the tubercle distally
• the opponens pollicis arises from the tubercle between flexor pollicis brevis and abductor pollicis brevis
• the abductor pollicis brevis arises from the tubercle proximally

Ligamentous

• two layers of the flexor retinaculum attach either side of the groove of the trapezium
• radial collateral ligament attaches to the lateral surface
• capsule of the carpometacarpal joint of the thumb attaches to the lateral surface

Relations

The tendon of flexor carpi radialis runs through the groove and the radial artery is directly related to the dorsal surface.

Arterial supply

Supplied by distal branches of the radial artery, primarily via the dorsal surface ².

Venous supply

Drained by tributaries of the radial vein.

Radiographic features

Plain radiograph

The trapezium may be visualized on a number of series of the distal upper limb including:

• hand radiograph
• wrist radiograph
• forearm radiograph

Cross-sectional imaging

CT or MRI imaging will demonstrate the trapezium and should be considered if there is clinical suspicion of occult injury. 

Development

Ossification

The trapezium begins to ossify in the fourth to fifth year.

Variant anatomy

Females have a significantly smaller sellar surface, with a fundamentally different shape of that surface ¹.

History and etymology

Trapezium derives from the Ancient Greek: originally 'small table', later a four-sided figure with no parallel sides.

Related pathology

• base of thumb arthritis
• trapezium fracture