Metacarpal Fractures

Metacarpal fractures are common hand injuries, especially in young men, and most heal well without surgery.

The main patterns are the boxer's fracture (fifth metacarpal neck, the commonest), shaft fractures, and fractures of the thumb metacarpal base (Bennett and Rolando). A wound over a knuckle after a punch is a fight bite, an open joint injury, until proven otherwise.

Management turns on rotation, angulation, shortening, joint involvement and whether the skin is broken. Rotational deformity matters most, because it does not remodel.

Each metacarpal has a base, shaft, neck and head. The deep transverse metacarpal ligaments link the second to fifth metacarpal heads and limit shortening and rotation. The fourth and fifth carpometacarpal (CMC) joints are more mobile than the second and third, so the ulnar metacarpals tolerate more angulation.

Patterns:

• •Boxer's fracture: fifth metacarpal neck, apex-dorsal angulation, usually from punching
• •Shaft fractures: spiral and oblique fractures tend to rotate and shorten; transverse fractures tend to angulate
• •Bennett fracture: a 2-part intra-articular fracture of the thumb metacarpal base; a small volar-ulnar fragment stays tethered to the trapezium while abductor pollicis longus pulls the shaft proximally and radially, so it is a fracture-dislocation
• •Rolando fracture: a comminuted Y- or T-shaped intra-articular fracture of the thumb base, with a worse outlook
• •Reverse Bennett: a fifth metacarpal base fracture-dislocation, displaced by extensor carpi ulnaris
• •Fight bite: a tooth breaches the metacarpophalangeal (MCP) joint capsule of a clenched fist