At the base of the wrist, we have eight carpal bones anatomically arranged in two rows. The proximal row includes scaphoid, lunate, triquetrum, and pisiform bones, but the distal row – the hamate, capitate, trapezium, and trapezoid bones. The arrangement of carpal bones in two rows poorly correlates with the wrist's kinesiology* but is universally accepted as the main anatomical classification.
Os scaphoideum is the greek-origin word meaning the boat-like bone (gr. skáphē – the boat). The shape of the bone corresponds well to the name – it is convex on one side (articular surface with the radius) and concave on another (articulation with os capitaum). Another slightly laterally faced elongated convex surface articulates with the trapezoid and trapezium bone.
Os Lunatum
Os lunatum from Latin lunatus – "crescent" is the small half-moon-shaped bone between the radius and the capitate bone. The lunate, scaphoid, and triquetrum bone's convex surfaces articulate with the radius within the radiocarpal joint.
Os Triquetrum
Os triquetrum name derives from the Latin triquetrus – triangular. Despite the name, the bone's shape is not always triangular, but somewhat elliptical or irregular. The main peculiarity allowing to differentiate this bone from other carpals is the flat and nearly perfectly round articular surface with the pisiform bone.
Os Pisiforme
Os pisiforme is the pea-size bone (from the Latin pisiformis – pea-shaped) with the only articular surface faced toward the os triquetrum.
Os Hamatum
Os hamatum is the triangular-shaped bone with the large ventrally directed hook (from the Latin hamulus – hook). It is designed to border the lateral wall of the carpal canal.
Os Capitatum
The capitate bone is the central and usually the largest one carpal bone. The most prominent feature of the capitate is the ovoid-shaped head (lat. caput) articulating with the three main first row carpal bones – scaphoid, lunate and triquetrum.
Os Trapezoideum
Os trapezoideum is usually the smallest carpal bone (when compared to other carpals from the same hand) with the wedge shape. The articular facets are polygonal, flat, or slightly convex. That lack of the saddle-shaped (trapezoid bone) or round pancake-shaped (triquetrum) articular surface allows distinguishing the trapezoid from other irregular carpal bones.
Os Trapezium
Os trapezium is of an irregular shape. It could be challenging to distinguish from other carpal bones unless you know that it articulates with the first metacarpal bone and therefore has a unique saddle-shaped articular surface (dotted line).
360° rotation of the hand bones
First published: 04/Oct/2020
Last update: 20/Dec/2020
