Trapezoid
Os trapezoideum
Also known as: lesser multangular
The smallest bone of the distal carpal row, wedge-shaped, lying between the trapezium and capitate and articulating with the base of the 2nd metacarpal.
Overview
The trapezoid is wedge-shaped with a broader dorsal than palmar surface — a keystone-like shape that helps lock the base of the index metacarpal. It articulates with the scaphoid proximally, trapezium laterally, capitate medially and the 2nd metacarpal distally, forming a rigid central column (with the capitate and 2nd/3rd metacarpals) — the stable "fixed unit" of the hand on which the mobile thumb and ulnar digits move. Isolated fractures are rare because it is well protected.
- Location
Distal carpal row, between the trapezium and the capitate.
Anatomy
- Articulations
Scaphoid, trapezium, capitate and 2nd metacarpal.
- Ossification
Single centre ≈5–6 years.
Function
- Stabilises the base of the 2nd metacarpal
- Part of the rigid central column of the hand
Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.