The trapezoid (lesser multangular) is one of the eight carpal bones of the hand. It lies in the distal row and is the smallest bone in this row, articulating with the trapezium laterally and the capitate medially. It also articulates with the scaphoid proximally and the index metacarpal distally.
The trapezoid bone (navicular refers to the scaphoid, greater multangular to the trapezium and 2nd metacarpal to the index metacarpal)
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The trapezoid is small and irregularly shaped. It has a rough dorsal surface, slightly larger than the equally rough palmar surface which also slopes laterally. The distal surface is triangular in shape, convex transversely but concave from palmar to dorsal. The medial surface bears a concave facet for articulation with capitate. Similar facets exist on the proximal surface for articulation with scaphoid and on the lateral surface for articulation with trapezium.
- Articulates with the scaphoid at the midcarpal joint
- Articulates with the trapezium at its intercarpal joint
- Articulates with the capitate at its intercarpal joint
- Articulates with the index metacarpal at its carpometacarpal joint
The trapezoid begins to ossify in the fourth to fifth year.
The trapezoid fractures rarely, usually only in association with other carpal fractures.