Unexpected motor axons in the distal superficial radial and posterior interosseous nerves: a cadaver study.

The prevalence of motor variations in the nerves supplying muscles of the first web space was evaluated by a visual dissection and immunohistochemical analysis from 56 cadaver hands. By microscopic visualization, 30% of the superficial radial nerves (SRNs) sent branches into muscles of the first web space. Since these unexpected penetrating branches were expected to be sensory or proprioceptive, markers of sensory and motor axons were used for confirmation. Positive identifications of motor axons (as identified by positive immunostaining for choline acetyltransferase) were made in 30% of SRNs and in 28.5% of posterior interosseous nerves. Classical teachings that the SRNs and PINs are exclusively sensory have been brought into question. Our data are in agreement with the rare clinical finding that motor function occasionally persists following devastating injury to both the ulnar and median nerves. Anatomic prevalence for this variation appears much higher than previous descriptions have indicated.