Boxer's fracture

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Introduction

Metacarpal fractures occur frequently among the general population and report for 40% of all hand fractures. The Fracture of the fifth metacarpal neck also known as Boxers Fracture, named after the classic mechanism of injury in which direct trauma is applied to a clenched fist or fall directly onto the hand. Boxer's fracture account for 10% of the metacarpal fractures which particularly occur in contact sports. Nearly, one-fourth of cases occur during athletic events.

Epidemiology/Etiology

Hand fractures constitute about 40% of all acute hand injuries, and they constitute about 20% of all fractures occurring below the elbow. Metacarpal fractures typically occur in patients aged 10-40 years, and men are more likely to be affected than women.  Young men sustain metacarpal fractures secondary to a punching mechanism or a direct blow to the hand while geriatric females sustain these injuries secondary to a low energy fall. The incidence rate of fracture seen in association with each digit metacarpal bone increases from the radial to the ulnar side. The incidence rate of 2nd metacarpal fractures is lower than the incidence rate of 5th metacarpal fractures.

Pathophysiology

Each metacarpal bone comprises of a head located distally, neck, body, and base which is located proximally. Fractures occur as a result of axial load to a clenched fist which causes direct trauma to the metacarpal bone, commonly resulting in apex dorsal angulation due in part to the forces exerted by the pull of the interosseous muscles. These interosseous muscles originate from the metacarpal shafts and insert onto proximal phalanges, responsible for adduction and abduction of the fingers. The collateral ligaments should be taken into consideration during splinting to minimize the risk of loss of motion due to shortening of the ligaments. The ligaments are taut in flexion, and more slack in extension, therefore The MCP joints should be splinted in flexion to prevent shortening (intrinsic plus positioning) since these ligaments are taut in flexion and more slack in extension. When the arteries and nerves supplying the fingers are adjacent to the metacarpal bones are injured in severely displaced Boxer’s fractures, which then require surgical intervention.

Characteristics/Clinical Presentation

Patients with Boxer’s fractures present with complaints of dorsal hand pain, swelling, and sometimes possible deformity in the setting of one of the mechanisms typically associated with this injury involving direct trauma to the hand.

Assessment of a potential Boxer’s fracture should comprise of an examination of the entire hand with comparison to the contralateral hand and should include examination of :

• Skin: Closely inspect the skin for any breaks, especially near the metacarpal head, typically the point of impact. When a Boxer’s fracture is sustained by a blow to the face, the recipient’s tooth may cause a laceration or abrasion known as a “fight bite." This may require operative irrigation and debridement.
• Neurovascular exam: As with all suspected fractures, a neurovascular exam should test for sensation, motor function, and blood flow distal to the injury.
• Angulation: Boxer’s fractures are typically associated with apex dorsal angulation, thereby resulting in depression of the MCP joint and loss of the normal knuckle contour. With significantly angulated fractures, “pseudo-clawing” may be observed due to damage to the extensor apparatus; pseudo-clawing is a hyperextension of the MCP joint and flexion at the PIP joint. The degree of angulation is determined using plain films.
• Rotational alignment: Any degree of malrotation warrants referral to a hand surgeon and therefore assessment of rotational alignment is a crucial component of the physical exam. Alignment can be assessed by examining the hand with the MCP and PCP joints in flexion, and DIP joints extended. If lines are drawn along the digits and extended distally, normally aligned digits will show the convergence of these lines. If the line extended from the fifth finger does not converge towards the others, suspect malrotation.
• Malrotation can also be detected by examining the hand with the MCPs flexed, and PCPs and DIPs extended. The fingernails should be in line along a single plane.

Management

The treatment for a Boxer’s fracture differs based on whether the fracture is open or closed, characteristics of the fracture including the degree of angulation, shortening, and rotation, and other concomitant injuries. Immobilization with an ulnar gutter splint may be the definitive treatment for closed, non-displaced fractures without angulation or rotation, while open fractures, significantly angulated or malrotated fractures or those involving injury to neurovascular structures may require operative fixation.