Posterior interosseous nerve palsy.

Eleven patients with non-traumatic paralysis of posterior interosseous innervated muscles were divided into three types, and the association between the type of paralysis and sites of compression was investigated. Type 1 (drop finger and thumb) showed a simultaneous compression of the recurrent branch and the descending branch at the entrance point and within the supinator. Type 2 (drop fingers) had compression of the recurrent branch alone, and Type 3 (drop thumb) had compression of the descending branch alone. The exit point from the supinator is considered to be the site of compression in Types 2 and 3.