Boxing Knuckle and CMC Injuries, Thumb UCL and Dart Throwing Motion

The sagittal bands form the extensor hood and keep the central extensor tendon centered over the knuckle as the finger flexes. Ian shows a boxer whose index finger tendon shifts toward the thumb because of a tear on the ulnar side. At the CMC joints, the index and middle fingers allow only about five degrees of motion, while the ring and little fingers allow up to 30, which is why a correct punch lands on the first two knuckles. If the wrist drops on impact, dorsal CMC structures can be damaged. The thumb's MCP ulnar collateral ligament is often injured by forced extension and abduction, and the volar plate is frequently involved too. Protection for the first three to six weeks can avoid chronic instability. The midcarpal joint, made up of the STT joint and the joint between the proximal row and the capitate and hamate, couples extension with radial deviation and flexion with ulnar deviation. Ian's PhD on boxers' wrist kinematics confirmed this pattern on impact. This coupling can guide mobilizations and early range work.