After exiting the spiral groove, the radial nerve supplies the brachioradialis muscle before dividing into the posterior interosseous branch and a sensory branch. The posterior interosseous branch is a pure motor nerve that supplies the supinator. It then dives into the supination through the fascia to supply the muscles of wrist and finger extension. This fascia is another common site for nerve damage to occur. The sensory branch that arises approximately at the elbow travels down the forearm, becoming superficial at the wrist before it supplies the lateral aspect of the dorsum of the hand.
Symptoms are dependent on the site of lesion.
The most common complaint is wrist drop. If the lesion is high above the elbow, then numbness of the forearm and hand may be an additional complaint. If the lesion is in the forearm, sensation is typically spared despite the wrist drop. Pain in the forearm resembling tennis elbow may be prominent. This presentation is initially acute for several days to weeks.