The metacarpal heads are the rounded far ends of the five metacarpal bones. They form the knuckles of a clenched fist and articulate with the bases of the proximal phalanges at the metacarpophalangeal (MCP) joints. The 2nd and 3rd heads are the most prominent and take most of the load in a well-placed punch.
| Articulations |
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|---|---|
| Landmarks |
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| Ossification | The 2nd-5th metacarpals have their growth plate at the head; these secondary centres appear at about 1-2 years and fuse at about 14-19 years. The 1st metacarpal head ossifies from the primary shaft centre. |
A punch with the little-finger side of the fist often breaks the neck of the 5th metacarpal (boxer's fracture), seen as a flattened or missing knuckle. A small wound over a knuckle after a punch may be a human tooth injury and needs urgent assessment because joint infection develops quickly. Swollen, tender MCP joints with a positive squeeze test are an early sign of rheumatoid arthritis.
Ask the person to make a fist: the knuckles are the metacarpal heads, and the joint lines sit just beyond them. With the fingers flexed at the MCP joints, the dorsal and side surfaces of each head can be felt clearly; with the fingers straight, the heads lie under the skin just behind the knuckle creases. On the palm side they sit under the distal palmar crease.
Fracture of the neck of the 5th (sometimes 4th) metacarpal from punching, leaving a depressed knuckle and sometimes a rotated finger.
A tooth cut over a knuckle that can carry mouth bacteria into the MCP joint and cause septic arthritis.
Inflammatory swelling of the MCP joints that, if untreated, can lead to ulnar drift of the fingers.
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