The middle metacarpal (third metacarpal) is one of the metacarpal bones, found within the substance of the hand at the base of the middle finger. It articulates with the capitate proximally, the index metacarpal proximolaterally, the ring metacarpal proximomedially and with the proximal phalanx of the middle finger distally.
The middle metacarpal (2nd and 4th metacarpal refer to the index and ring metacarpals)
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The middle metacarpal can be felt running down from the knuckle of the middle finger on the dorsum of the hand. The metacarpal head forms much of the substance of the knuckle when the finger is flexed.
The middle metacarpal possesses a base, shaft and head as with the other metacarpals. The base is unique in possessing a short styloid process which points proximally from the lateral side of the dorsal surface. The facet for capitate is largely convex except beneath the styloid process where it becomes concave. Two small facets on the medial side articulate with the ring metacarpal, whilst a small facet on the lateral side articulates with the index metacarpal. The shaft and head are similar to that of the index metacarpal, the shaft resembling a prism in cross-section.
- Adductor pollicis has two heads:
- The oblique head arises from a large crescent-shaped area towards the base of the palmar surface
- The transverse head arises from a large area on palmar surface of the midshaft
- The second dorsal interosseous arises from the lateral aspect of the dorsal surface
- The third dorsal interosseous arises from the medial aspect of the dorsal surface
- Extensor carpi radialis brevis inserts into the dorsolateral aspect of the base
- Flexor carpi radialis inserts into a small area on the lateral aspect of the palmar surface of the base
In addition, dorsal, palmar and interosseous ligaments connect the middle metacarpal to the other metacarpals.
The extensor and flexor tendons of the middle finger are located on the dorsal and palmar aspects of the metacarpal, respectively.
The styloid process may sometimes be a separate ossicle.
- May be fractured