It is well known that variations of the innervation in intrinsic had muscles are common. A detailed anatomic study revealed that Riche-Cannieu anastomosis, a neural anastomosis between the recurrent branch of the median nerve and the de branch of
the
ulnar nerve, was in 77% of cadaveric dissections. Few electrophysiologic study of such anastomosis, however, has been done in a large population.
The first group studied consisted of 88 limbs of 44 unselected subjects without Martin-Gruber anastomosis(MGA). The compound muscle action potentials(CMAP) were recorded by surface electrodes placed over the abductor pollicis brevis(APB), first
dorsal
interosseous(FDI), and abductor digiti quinti(ADQ) muscles with the stimulation at the wrist. The innervation of FDI by the median nerve was detected in 81(92.1%) of 88 limbs, and the innervation of APB by the ulnar nerve in 77(87.5%). In no
case,
innervation of ADQ by the median nerve was found. The mean median nerve innervation ratio(MNIR) of FDI was 8.8%, and mean ulnar nerve innervation ratio(UNIR) of APB 23.5%.
The second group, 37 MGA-detected limbs of 27 subjects, was also studied in order to evaluate the contribution of MGA to the innervation in intrinsic hand muscles. There was no significant difference in the incidence of anomalous innervation of
each
muscle in both groups.
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