The hand neural communication between the ulnar and median nerves: Electrophysiological detection

One hundred and fifty hands of 85 unselected subjects were studied. Supramaximal nerve stimulation of the median and ulnar nerves at the wrist and elbow were used. The compound muscle action potentials (CMAPs) were recorded from the abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles. In 125 of 150 hands (83.3%), the ulnar to median nerve communication in the hand was demonstrated. The median to ulnar nerve communication in the hand was detected in 65 of 150 hands (43.3%) when recorded the CMAP from the FDI, and was detected in 24 hands (16.0%) when recorded from the ADM. The mean ulnar nerve innervation ratio in the APB was 27.6 ± l6.4% (mean ± S.D.). This mean value was significantly smaller in the American blacks than in the American caucasians or hispanics (mainly born in Cuba). The mean median nerve innervation ratio was 11.4 ± 15.1 and 6.2 ± 14.6% in the FDI and in the ADM muscles, respectively.