The Posterior Interosseous Nerve
The posterior interrosseous nerve is a nerve which travels along the posterior aspect of the forearm between the two bones of the forearm.

Symptoms
Posterior interrosseous nerve syndrome is characterized by symptoms similar to those of radial tunnel syndrome, but with the addition of weakness of the muscles that extend the wrist.  In the fingers, it can even result in muscle paralysis.

Treatment
Treatment consists of using antiinflammatory medication, splinting of the wrist and elbow, and rest.  A period of two to three months is generally allowed to see whether the problem will resolve, which happens with most people, but this depends on the amount of weakness present.  If there is no improvement with time, then surgical release of the radial nerve and the posterior interosseous nerve is needed.