Electrophysiological verification of the ulnar to median nerve communications in the hand and forearm.

One hundred and fifty upper extremities of 85 unselected subjects were studied. Supramaximal nerve stimulation of the median and ulnar nerves at the wrist and elbow was used and the compound muscle action potentials (CMAPs) from the abductor pollicis brevis (APB) muscle were recorded. The ulnar to median nerve communication in the hand -- Riche-Cannieu anastomosis -- was detected in 125 out of 150 hands (83.3%). The ulnar to median nerve communication in the forearm was demonstrated in only two out of 150 extremities (1.3%). The mean ulnar nerve innervation ratio (UNIR) in the APB was 27.6 +/- 16.4% (mean +/- S.D.). In the American black population, this UNIR percentage was statistically smaller than in the American caucasian or hispanic population (p less than 0.05).