Course Origins originates from the radial nerve at the radiohumeral joint line Course arcade of Frohse at radial head dives under supinator at arcade of Frohse (thickened edge of between heads of supinator) forearm posterior compartment winds around radial neck within substance of muscle to posterior compartment of forearm interosseous membrane reaches interosseous membrane of forearm and ends as sensation to dorsal wrist capsule dorsal wrist capsule Motor Innervation Motor common extensors ECRB (often from radial nerve proper, but can be from PIN) Extensor digitorum communis (EDC) Extensor digiti minimi (EDM) Extensor carpi ulnaris (ECU) deep extensors Supinator Abductor pollicis longus (APL) Extensor pollicus brevis (EPB) Extensor pollicus longus (EPL) Extensor indicis proprius (EIP) Senory Innervation Sensory sensory fibers to dorsal wrist capusle provided by terminal branch which is located on the floor of the 4th extensor compartment no cutaneous innervation Clinical PIN compression Syndrome in PIN palsy, the last muscle to recover is the extensor indicis proprius Dorsal Approach to Radius (Thompson)