Boxer's knuckle: Sonographic anatomy and assessment of sagittal band tears of the dorsal hood

The dorsal hood is a complex retinacular system of the hand. The sagittal bands are the most important stabilising component of the extensor tendons overlying the metacarpophalangeal joint. Sagittal band tears can occur following blunt or repetitive trauma to the hand resulting in what is known as Boxer’s knuckle. Partial or complete sagittal bands can occur and result in extensor tendon subluxation or dislocation which may be clinically underappreciated. Ultrasound imaging using long and short axis imaging of the metacarpophalangeal joint and its surrounding structures has advantages over magnetic resonance imaging as it is dynamic, quick and can be performed in the emergency setting. Familiarity with the detailed relative sonographic technique, and normal and abnormal sonographic appearances of the structures of and around the metacarpophalangeal joints and fingers is essential allow a timely sonographic diagnosis of sagittal band tears and any associated tendon instability to optimally guide patient management.