Anatomical variation of the posterior interosseous nerve: a cadaver dissection study.

An anatomical variation of the posterior interosseous nerve was found in a cadaver. The posterior interosseous nerve entered the supinator muscle 3 cm distal to the radiohumeral joint, but exited from two sites. Fifty percent of the nerve exited under the distal edge of the supinator muscle. The other 50% of the nerve pierced through the supinator muscle, 4.2 cm distal to the articular surface of the radial head and then joined the remaining posterior interosseous nerve as it emerged from the supinator muscle distally. Variations were not found concerning the order and the manner of branches to the muscles. This variation in the posterior interosseous nerve could be an additional compression site for this nerve and therefore responsible for some of the atypical presentations of symptoms and for partial recovery after surgical decompression. Careful surgical dissection is recommended to avoid injury to this branch.