End-to-side nerve repair: review of the literature.

End-to-side (ETS) nerve repair, in which the distal stump of a transected nerve is coapted to the side of an uninjured donor nerve, offers a technique for repair of peripheral nerve injuries where the proximal nerve stump is unavailable or a significant nerve gap exists. Details of animal models are explored including motor and sensory regeneration to further clarify the mechanism of collateral sprouting while eliminating false positive results from contaminating axons. Some experimental studies support the conclusion that sensory or motor reinnervation may be derived from collateral sprouting while others suggest that reinnervation requires an injury to the donor nerve. Clinical experience with ETS neurorrhaphy includes management of upper extremity nerve injury, facial reanimation, reconstruction following tumor ablation, and the prevention of neuroma formation. Our interpretation of the ETS literature suggests that sensory axons may sprout without deliberately attempting to injure them, while motor axons regenerate only in response to a deliberate injury. Experimental and clinical experience with ETS neurorrhaphy has rendered mixed results. Our interpretation of the literature suggests that the success of this technique is dependent upon axonal injury of motor and possibly sensory nerves. While continued clinical and laboratory experimentation with ETS nerve repair is warranted, it should not yet replace more established techniques of nerve repair.