Clinical and neurophysiologic characteristics of the pronator syndrome.

Nine patients were clinically diagnosed as having a pronator syndrome, i.e., high median nerve compression. The main symptom was pain at the proximal volar aspect of the forearm increasing for several hours after exercise. All patients showed local tenderness over the median nerve 4-5 cm distal to the elbow and pain on active forearm pronation against resistance. Two patients had been previously operated upon for carpal tunnel syndrome. Preoperative routine neurographic-electromyographic studies were normal. In the differential diagnosis, the exclusion of carpal tunnel syndrome and anterior interosseous nerve entrapment is most important. On active isometric forearm pronation, interference with median nerve motor conduction occurred in three patients preoperation. This phenomenon had disappeared following median nerve decompression at the level of the pronator muscle. Fibrous bands from the pronator muscle, encircling the nerve, seemed to be an etiological factor. Eight of nine patients were either improved or recovered completely by surgical treatment.