Trapezium

Os trapezium

Also known as: greater multangular

The lateral bone of the distal carpal row, at the base of the thumb, whose saddle-shaped distal surface forms the highly mobile carpometacarpal joint of the thumb.

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Overview

The trapezium articulates with the scaphoid proximally, the trapezoid medially, and the 1st metacarpal (saddle joint) and part of the 2nd metacarpal distally. Its palmar surface carries the tubercle of the trapezium (lateral attachment of the flexor retinaculum, origin of thenar muscles) and, medial to it, a groove for the tendon of flexor carpi radialis, which runs in its own compartment within the retinaculum. Its saddle-shaped first carpometacarpal joint permits flexion, extension, abduction, adduction, circumduction and opposition of the thumb — the movement that makes the human hand so dexterous.

Location: Lateral end of the distal carpal row, at the base of the thumb.

Anatomy

Articulations: Scaphoid, trapezoid, 1st and 2nd metacarpals.
Ossification: Single centre ≈5 years.

Function

Forms the saddle joint of the thumb, enabling opposition
Attachment for the flexor retinaculum and thenar muscles

Clinical significance

Thumb base (first CMC) osteoarthritis

Very common in postmenopausal women: pain at the thumb base on pinching, "squaring" of the thumb base and positive grind test; trapeziectomy is an established operation.

Mnemonics

Trapezium vs trapezoid

"Trapezium is by the thumb"; the trapezoid is next to it, medially.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.