Metacarpal Fractures and Boxer's Fracture
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Direct answer
A boxer's fracture is a fracture of the neck of the fifth metacarpal, usually from a clenched fist striking a hard object, with the head displaced volarly and the apex angled dorsally. Acceptable volar angulation is limited, while rotational malalignment is not tolerated because it overlaps the fingers. A human bite over the knuckle makes the fracture an open injury needing urgent antibiotics.
What you must remember
- Site and mechanism: neck of the fifth metacarpal, from a punch with a closed fist, and sometimes the neck of the fourth.
- Deformity: the metacarpal head is pushed volarly with dorsal apex angulation, which is visible on a lateral view.
- Tolerance of angulation: modest volar angulation at the fifth neck is tolerated, with texts quoting a figure around 40 degrees, and the books differ on the precise limit.
- Rotation: rotational malalignment is never accepted, because a rotated finger overlaps its neighbours when the hand closes.
- Fight bite: a human tooth wound over the metacarpophalangeal joint is an open injury, classically infected with Eikenella corrodens.
- Management: most closed boxer's fractures are reduced if needed and splinted, with early active movement, while unstable or rotated fractures are fixed.
- Other metacarpals: shaft and base fractures of the other metacarpals follow similar principles, with rotation and articular involvement deciding surgery.
A pathway for a clenched-fist injury
The sequence matters because a closed boxer's fracture and a fight bite look similar at first, but they call for very different care. The steps below follow the usual path in the emergency department and clinic.
- Take the history: ask how the injury happened, because a punch into a person's teeth changes the diagnosis to an open injury.
- Examine the wound: look for a skin break over the knuckle, and explore it gently if a bite is possible.
- Image the hand: obtain posteroanterior and lateral views to judge angulation, length and rotation.
- Check rotation: compare the finger with its neighbours in flexion, since rotation is the main criterion for surgery.
- Reduce and splint: if angulation is excessive, reduce and hold the fracture in an ulnar gutter or buddy-taping position.
- Treat any bite: clean the wound, start antibiotics active against oral flora and consider admission if the infection is established.
Where the exam tries to catch you
Most lost marks come from dismissing a bite wound or from accepting rotational malalignment.
- Trap: a boxer's fracture with a small wound over the knuckle is a simple closed fracture. Correct: a wound from a punch into teeth is a fight bite, an open injury needing antibiotics and wound care.
- Trap: the fifth metacarpal can tolerate any degree of angulation because it is a small bone. Correct: modest volar angulation is accepted, but texts quote a limit, and rotation must be corrected.
- Trap: a fight bite is treated with cloxacillin or a first-generation cephalosporin. Correct: Eikenella corrodens is resistant to these, so an amoxicillin-clavulanate type regimen is the textbook choice.
Frequently asked questions
What is a boxer's fracture?
A boxer's fracture is a fracture of the neck of the fifth metacarpal, usually caused by a clenched fist striking a hard object. The metacarpal head is displaced volarly with dorsal angulation of the apex.
How much angulation is acceptable in a boxer's fracture?
Modest volar angulation is acceptable in a boxer's fracture, with textbooks quoting a figure near 40 degrees at the fifth neck. The exact limit varies between books, but rotational malalignment is never acceptable.
Why is rotational malalignment important in metacarpal fractures?
Rotational malalignment is important in metacarpal fractures because a rotated finger overlaps its neighbours on flexing the hand. This causes a scissoring effect that affects function, so rotation must be corrected even when angulation is acceptable.
What is the treatment of a fight bite over the knuckle?
A fight bite over the knuckle needs wound cleaning, exploration and antibiotics that cover oral flora, including Eikenella corrodens. Admission for intravenous antibiotics is considered when the infection is established.