Lover not a fighter

There is a fracture of the right 5th metacarpal neck. The distal fragment is volarly displaced and angulated.

This is a Boxer’s fracture. A Boxer’s fracture is a metacarpal neck fracture affecting the 5th metacarpal.

The name is ironic because someone who knows how to punch will avoid focusing the impact of a blow on the knuckle of his or her little finger. Perhaps it should be renamed the ‘I’m a lover, not a fighter, fracture’?

Assume any wound associated with a Boxer’s fracture is a ‘fight bite’.

Metacarpal neck fractures result from direct impact on the metacarpal head with the MCP joint in flexion. This generally occurs when the patient’s fist strikes a solid object like a wall or someone else’s head…

AP, lateral and oblique views should be obtained to accurate define metacarpal neck fractures, and the degree of displacement and angulation.

In this case, the true lateral is missing — this is an important view as it provides the most accurate assessment of angulation.

Complications can be debilitating:

• Collateral ligament damage.
• Extensor tendon injuries.
• Rotational deformity leads to finger overlap and impaired function.
• Dorsal bony prominence with compromise of the extensor mechanism.
• Clawing of the finger may occur if the reduction is incomplete or unstable.
• Chronic pain with grasp.
• Nonunion is rare.

Any rotational deformity in a metacarpal neck or shaft fracture should be corrected as it is poorly tolerated. This can be assessed by getting the patient to make a fist — rotational deformity will cause the fingers to cross.

Flexion deformities are more common, and better tolerated. A simple rule of thumb for the amount of volar angulation tolerate is:

• 10 degrees for the 2nd metacarpal.
• 20 degrees for the 3rd metacarpal.
• 30 degrees for the 4th metacarpal.
• 40 degrees for the 5th metacarpal.

Simon et al (2007) suggests reduction for deformities 10 degrees less than those detailed above for 3rd/4th/5th metacarpal neck fractures. Rosen’s says 15-15-35-45!

Note that the 5th MC neck normally has a volar angulation of 15 degrees — the above allowances are in addition to this.

The 5th CMC joint is much more mobile — like the thumb — so a greater degree of flexion deformity is functionally acceptable (similarly ~40 degree flexion is acceptable for 1st metacarpal fractures).

Metacarpal neck fractures are inherently unstable.

Management of 4th and 5th metacarpal neck fractures:

• nondisplaced, nonangulated —
  RICE
  immobilisation with a volar splint to the palmar crease and a dorsal splint extending to, but not including, the PIP. Wrist in 30 degrees extension and MCPJ flexed to 90 degrees.
  Begin PIP and DIP movements immediately, protected MCP movements after 3-4 weeks.
• displaced, angulated —
  Reduction may be performed under a hematoma block, wrist block or even procedural sedation. After disimpacting the fracture, the MCPJ and PIPJ is flexed to 90 degrees (‘the 90-90 method’) — this tightens the collateral ligaments that connect the PIP to the MC head. A volar force is applied over the shaft proximal to the fracture line at the same time as a dorsally directed forced applied to the flexed PIP.
  immobilise as for the nondisplaced/ nonangulated fracture +/- an ulnar gutter splint.
  Close follow up is required as reductions are unstable and pin fixation is usually necessary.

Management of 2nd and 3rd metacarpal neck fractures:

• Nondisplaced, nonangulated —
  RICE
  immobilization in a radial gutter splint  extending from the distal elbow just proximal to the PIP joint. The wrist should be in 20 degrees extension and the MCPJ should be in 50-60 degrees flexion.
  Close follow-up to detect angulation or rotational malalignment is crucial as displacement is difficult to correct if detected >1 week. Re-xray 4-5 days post-injury.
• displaced, angulated —
  RICE, radial gutter splint as above
  Refer early for pinning

Fractures through the metacarpal head, involving the articular surface, require operative fixation.