Boxer knuckle (injury of the extensor hood with extensor tendon subluxation): diagnosis with dynamic US--report of three cases.

The use of dynamic ultrasonography (US) in diagnosing traumatic and nontraumatic extensor tendon dislocations in fingers of three subjects is reported. Dynamic US of the clenched fist in two patients with traumatic injury revealed dislocated but grossly intact tendons surrounded by soft-tissue edema; magnetic resonance (MR) imaging in one patient indicated similar findings. Rupture in the sagittal band of the extensor hood mechanism in the two patients was confirmed at surgery. The third subject, an asymptomatic volunteer, had a congenital tendency toward dislocation. Dynamic US of the clenched fist is useful in diagnosing injuries of the extensor hood mechanism.