**1. Introduction**

Clinically, traumatic peripheral nerve injuries are common, and are caused by violence, recreational activities, motor vehicle accidents, and iatrogenic injuries during surgery. The majority of nerve injuries occur in the upper extremity [1] with about 1–3% of all upper extremity trauma patients presenting with nerve injuries [2]. These injuries can be severely debilitating and have a significantly negative impact on the individual's lifestyle, function, and work [3,4]. The majority of those who su ffer traumatic nerve injuries are young, with an average age of 39 [5]. Less than 50% of such individuals undergo nerve repair surgery, and of those who do, only 40–50% recover good function [6]. Thus, the majority of individuals who su ffer peripheral nerve traumas su ffer permanent neurological deficits, and frequently also chronic neuropathic pain associated with the nerve injury.

Due to the generally limited extent of neurological recovery, it is essential to develop novel techniques that restore more extensive function to a larger number of patients. This review examines the relative e fficacies of di fferent techniques that have been tested for their ability to restore function

and discusses a novel technique that shows grea<sup>t</sup> promise for inducing recovery under conditions where it is presently not possible.

#### **2. Issues Influencing the Extent of Axon Regeneration and Neurological Recovery**

#### *2.1. Type of Nerve Trauma*

The type of nerve injury has a major influence on the extent of neurological recovery. Following a traumatic nerve injury, sometimes referred to as an "untidy" wound (shrapnel, bullet, blunt object, open fracture, contaminated), there is significantly less recovery than following a "tidy," or clean-cut, injury (glass, knife, scissors) [7]. This is because untidy injuries damage longer lengths of the nerve, which must be removed, resulting in longer nerve gaps, from which recovery is less than for short gaps.

Another type of nerve injury involves the loss of nerve vascularization, such as occurs with untidy injuries. When nerves lose their blood supply, a significantly lower percentage of those repaired nerves recover function than those following the repair of a tidy injury [7]. This is because of the time required for the nerve graft to be re-vascularized, during which axons do not, or are permanently prevented from, regenerating into the non-vascularized portion of the nerve.
