WEAKNESS of the muscles innervated by the posterior interosseous nerve in patients with no history of trauma to the upper extremity is a rare clinical entity. This weakness can result from entrapment of the nerve by tumor, inflammation, or anatomic anomaly. If suspect, the diagnosis of nerve entrapment can be made clinically and proved with electromyography. Early diagnosis often allows successful surgical treatment.
Functional Anatomy
The posterior interosseous nerve or deep radial nerve (Fig 1) is the larger terminal division of the radial nerve.1 Descending across the elbow under cover of the brachioradialis and extensor carpi radialis longus muscles, it supplies the extensor carpi radialis brevis and supinator muscles before reaching the proximal border of the latter. Entering the supinator, the deep radial nerve winds around the lateral side of the radius in the substance of the muscle. It passes through the muscle lengthwise between two thin