The index metacarpal (second metacarpal) is the long bone found within the substance of the hand at the base of the index finger. It articulates with the trapezium, trapezoid and capitate proximally, the middle metacarpal proximomedially and with the proximal phalanx of the index finger distally.
The index metacarpal (greater multangular refers to the trapezium, lesser multangular to the trapezoid and 3rd metacarpal to the middle metacarpal)
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The index metacarpal can be felt as a bony ridge on the dorsum of the hand, proximal to the knuckle.
The index metacarpal has the longest shaft and largest base of all the metacarpals. The base has a large proximal facet for articulation with trapezoid, with a smaller lateral facet for trapezium and a larger facet on the medial side of the base for capitate and the middle metacarpal. There is a small tubercle on the palmar surface. The shaft has a prism shape in cross-section and is curved, convex dorsally. The dorsal surface is broad at the head, becoming thinner proximally. There are small tubercles on either side of the head. The lateral surface is sloped dorsally, as is the medial surface, which is divided into dorsal and palmar aspects by a small ridge.
- The oblique head of adductor policis arises from the medial surface of the palmar aspect near the base
- The second palmar interosseous arises from the centre of the palmar surface
- The first dorsal interosseous arises from the lateral aspect of the dorsal surface
- The second dorsal interosseous arises from the medial aspect of the dorsal surface
- Flexor carpi radialis inserts into the palmar surface of the base at the tubercle
- Extensor carpi radialis longus inserts into the dorsal surface of the base
In addition, dorsal, palmar and interosseous ligaments connect the index metacarpal to the other metacarpals.
The extensor and flexor tendons of the index finger are located on the dorsal and palmar aspects of the metacarpal, respectively.
A proximal ossification centre may appear in the second metacarpal.
- May be fractured