Boxer fracture

Boxer fractures are minimally comminuted, transverse fractures of the 5^th metacarpal and are the most common type of metacarpal fracture. They typically occur (as the name suggests) when punching and are a common sight in all emergency departments on Friday nights. 

They should not be confused with a boxer's knuckle knuckle which represents tendinous and ligamentous disruption of the metacarpal phalangeal joint. 

Mechanism 

Boxer fractures are an impaction injury (axial loading of the 5^th metacarpal) almost always result as a consequence of a direct blow with clenched fist against a solid surface. Typical solid sufaces are human faces or walls. It is therefore no surprise that young adult males are by far the most commonly affected group (~95%) ¹.  

In most cases the fracture is in a transverse plane and minimally impacted. It is usually angulated in a volar direction. Spiral fractures or angulation in other directions are also sometimes encountered. 

Radiographic features

Plain radiographs are in almost all cases the only imaging required. 

Plain films

Typically the fracture appears in the transverse plane through the metacarpal neck, with volar angulation of the distal fragment. Spiral fractures, which are less common, can be harder to visualise ². 

Features which should be commented upon include:

• morphology of the fracture: transverse, spiral, comminuted, oblique etc.
• intra-articular extension, and degree of articular step-off
• degree of impaction/shortening
• degree of angulation
• degree of rotation: angulation on AP film implies a degree of rotation

The degree of palmar angulation is best assessed on lateral radiograph, with lines drawn through the medullary canal. When this is not possible the oblique view can be used, however this results in less accurate measurements which tend to overestimate the degree of angulation ⁶. 

Report checklist

In addition to stating that a fifth metacarpal fracture is present, a number of features should be evaluated and commented up:

• fracture
  • location, especially distance along the shaft
  • comminution
  • involvement of articular surface of the MCP joint
  • degree of angulation
  • presence of rotation: this is critical! - see(see below)
• assess for any associated fractures and/or dislocations

Treatment

Although it can be treated conservatively, it is relatively unstable, and K-wire fixation is often required for better cosmetic results.

Closed reduction can be achieved by stabilising the proximal part of the metacarpal dorsally and applying pressure to the head of the metacarpal from the palmar aspect, while flexing the proximal phalanx ³.  An ulnar nerve block may help ⁵. 

A degree of residual palmar angulation is acceptable. The apex dorsal angulation for neck fractures should not exceed 30-40 degrees ^3-4. When the fracture is of the shaft less deformity is acceptable (less than 20 degrees). If angulation exceeds this, palmar pain and reduction of strength may be present on gripping ³. 

No rotational deformity is acceptable as this can lead to significant disability, with the little finger overlapping other digits during flexion ⁴. Articular step-off in cases with intra-articular extension should be no more than 1-2 mm ⁴.  

A short arm gutter-splint is applied, with flexion of the metacarpophalangeal joint, typically for 2-3 weeks followed by buddy-strapping ^4-5. Prolonged immobilisation can lead to stiffness. 

Fractures of the fourth metacarpal neck can be treated in a similar fashion, whereas the second and third metacarpals usually require internal fixation ⁵. 

History and etymology

Boxer fractures are named after the common mechanism of injury, namely that of throwing a punch. It should be noted that only a poorly thrown punch results in this type of fracture, and such injuries are actually uncommon in professional boxers who are taught to transfer as much power as possible through the second and third metacarpals ^2,5. 

See also

• metacarpal fractures
• upper limb fractures
• fractures: general discussion