Radial tunnel syndrome (RTS) is a compressive neuropathy (without any motor deficits) affecting one of the terminal branches of the radial nerve, the posterior interosseous nerve (PIN), as it passes through the radial tunnel.
The concept is that the radial nerve becomes irritated and/or inflamed from friction caused by compression by muscles in the forearm.
Sometimes categorized into radial tunnel syndrome and PIN syndrome:
RTS: Painful condition without motor deficits
PIN syndrome: PIN motor neuropathy
Significant overlap in many cases, making some question the differentiation.
There is a much overlap between lateral epicondylitis and radial tunnel syndrome exam findings.
Note: PIN syndrome is distinct from RTS in that patients with PIN syndrome have a significant motor deficit. This includes loss of finger and thumb extension and radial deviation of the wrist during extension because of the consistent PIN innervation of the extensor carpi ulnaris as opposed to the extensor carpi radialis longus (which is usually innervated by the radial nerve proper).