The extensor carpi radialis brevis tendon is a long aponeurosis from the center of the forearm that inserts the extensor carpi radialis brevis muscle into the base of the 3rd metarcarpal bone. The extensor carpi radialis brevis muscle is a companion of the extensor carpi radialis longus and extends toward the middle of it. This muscle runs from the humerus (upper arm bone) to the bones in the hand Continue Scrolling To Read More Below...