Boxer’s knuckle, also called a sagittal band tear, is an injury caused by the repetitive blows absorbed and delivered by the clinched hand of a boxer. The knuckles (joints) of the middle and little finger are the most commonly affected. Boxer's knuckle is an injury to the extensor mechanism of the fingers. The extensor tendon runs across the metacarpophalangeal joint (MCP joint). Sagittal bands hold the tendon in place over the joint. Just under the tendon is the MCP joint capsule. The tendon, sagittal band, joint capsule, or any combination of the three may become worn and tear. The symptoms of boxer's knuckle include the following:
* pain, swelling, and tenderness of the affected knuckle
* possible popping sensation as the affected finger’s knuckle is bent
* obvious bulging that's palpable over the affected knuckle
* possible inability to bend or straighten the affected knuckle