Boxer knuckle (not to be confused with a boxer fracture) refers to an appearance when there is a disruption to the sagittal bands of the extensor hood, particularly over the metacarpophalangeal (MCP) joint.
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Epidemiology
It is most common in the middle finger, and radial sided sagittal band injuries are more common than ulnar sided band injuries 4.
Pathology
It often results after a clenched fist strikes an object in a traumatic situation. Less often, it can result in the absence of trauma, such as in an inflammatory arthritis (e.g. rheumatoid arthritis).
The ulnar and radial sagittal bands exert tensile forces in opposite directions during flexion, which keeps the extensor tendon in apposition with the metacarpal bone.
Radiographic features
Ultrasound
May show radial or ulnar subluxation/dislocation of the extensor tendons from their usual position 3. This can be better elicited on dynamic sonography.
Treatment and prognosis
Acute injuries can be managed in an extension splint for 6 weeks. Operative techniques include either direct repair, reconstruction procedures or joint fusion 5.
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