IntroductionThe p osterior interosseous nerve syndrome is caused by compression, in the upper third of the forearm, of the terminal motor branch of the radial nerve, called the deep radial nerve or posterior interosseous nerve (PIN). In most cases, this nerve is compressed at the arcade of Frohse. Proximally to this arcade, the main radial nerve and/or its branches, the sensory superficial radial nerve and the PIN, may be also compressed.