One of the five primary muscles that control the wrist, the extensor is a skeletal muscle originating from three areas; the humerus’ lateral supracondylar ridge, its lateral epicondyle, and also from the lateral intermuscular septum. From there, the muscle stretches across and attaches to the metacarpal of the index finger. Ending in a tendon on the top third of the forearm, it runs below both the abductor pollicis longus, and then the dorsal carpal ligament, alongside the radius’ lateral border.
Innervated by the radial nerve at various vertebrae, the extensors radially abduct the hands, moving them towards the thumb and away from the palmar side. In general, flexors and extensors work together to bend and straighten joints.