Functional Motor Nerve Regeneration Without Motor-Sensory Specificity Following End-to-Side Neurorrhaphy: An Experimental Study

Purpose To evaluate the quality of regenerating myelinated axons and motor-sensory specificity in an end-to-side nerve repair model. Methods We divided 20 rats into 3 groups: (1) end-to-side neurorrhaphy using the ulnar nerve as donor nerve and the musculocutaneous nerve as recipient nerve; (2) normal control; and (3) transected nerve with the stumps buried. At 5 months, we monitored the grooming test, the electrophysiological response, and the histologic changes in nerve and muscle. Results Grooming recovered successfully, and electrophysiological investigations revealed that the target muscles had been reinnervated in the end-to-side group. The mean wet weight of the reinnervated biceps brachii muscle was 72% of the normal muscle, and the mean muscle fiber cross-sectional area of the reinnervated muscle was similar to the normal muscle. The implanted musculocutaneous nerve contained varying but satisfactory numbers of axons (end-to-side group: 596 348 vs normal group: 1,340 241). Acetylcholinesterase staining revealed a similar percentage of myelinated fibers in the musculocutaneous nerve (39%) and the biceps brachii branch of the musculocutaneous nerve (38%) in the end-to-side group. This was similar to the number of myelinated fibers in the donor ulnar nerve (37%). Conclusions The present study confirms that limited but functional reinnervation can occur on the basis of collateral sprouting of intact axons from the ulnar nerve. The motor-sensory specificity is not important. (J Hand Surg 2011;36A:2010-2016. Copyright (C) 2011 by the American Society for Surgery of the Hand. All rights reserved.)