Each nerve is a cordlike structure that contains many axons, also called nerve fibers. Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the perineurium, which is a lamellated sheath of considerable tensile strength. Because of the diffusion barrier in the perineurium, the interior of the fascicles, the endoneurial space, is chemically isolated from the surrounding tissues, thereby preserving a specialized ionic environment. Finally, the fascicles are embedded within an epineurium, which is a supporting and protective connective tissue carrying the main supply channels of the intraneural vascular system: the epineural vessels. Usually, several fascicles are grouped together in fascicular bundles constituting well-defined subunits of the nerve trunk. Schwann cells encircle the axonal projections and produce myelin, which facilitates the electrical conduction along the nerve [14, 19].

Nerve fibers can be myelinated or nonmyelinated. In the myelinated fiber, one axon is associated with only one Schwann cell of whose membrane is being wrapped spirally around the axon, producing a sheath of alternating layers of lipid and protein: the myelin sheath. In nonmyelinated fibers, however, one Schwann cell accumulates a great number of axons. The Schwann cells, being arranged in a longitudinal sequence along the axons surface, meet each other at the nodes of Ranvier, where finger-like cellular processes interdigitate. At this location, there is a space between the processes, allowing extracellular ions to reach the axon [17]. This is an important process in the so-called saltatory propagation of impulses from node to node. In between the nodes of Ranvier, the compact myelin and cytoplasm within a Schwann cell are arranged in a series of concentric subcellular compartments surrounding the axon, insulating it both morphologically and physiologically from the endoneurium [46]. The axon has a core of axoplasm surrounded by a continuous plasma membrane: the axolemma. The surrounding concentric layers of Schwann cell cytoplasm and myelin are bound peripherally by a continuous Schwann cell plasma membrane and its basal lamina. In literature, this basal lamina, together with the endoneurial reticular and collagen fibers providing the framework supporting the nerve fiber, has been referred to as the endoneurial tube or endoneurial sheath [31].

Nerve fibers of the PNS are classified according to their involvement in motor or sensory, somatic or visceral pathways [9]. Mixed nerves contain both motor and sensory fibers. Sensory nerves contain mostly sensory fibers; they are less common and include the optic and olfactory nerves. Motor nerves contain motor fibers. Most of the peripheral nerves in body contain both motor and sensory nerve fibers [9].

The cell bodies of peripheral neurons are present in nervous structures called ganglia. There are two types of ganglia: autonomic ganglia and somatic-sensory ganglia. Autonomic ganglia possess sympathetic and parasympathetic postganglionic cells. Two types of somatic sensory ganglia exist: those associated with cranial nerves, i.e., cranial ganglia; and those associated with spinal nerves, i.e., spinal ganglia or dorsal root ganglia. The neurons in dorsal root ganglia are pseudounipolar neurons, and in this type of neurons, one single process, an axon, leaves the cell body and divides into two processes, one projecting to the CNS, and the other projecting to peripheral targets. Dorsal root ganglia neurons innervate muscle spindles and receptors in the skin [14]. The peripheral ganglia also contain glial cells such as satellite cells and Schwann cells (SCs). The glial cells regulate the neuronal environment by supporting and protecting the neurons. They can also produce neurotropic factors in response to neuronal injury. A ganglion also contains blood vessels and fibrobalsts. The entire ganglion is encapsulated in a connective tissue layer, which is continuous with the epineurium of the nerve.

When a nerve has been injured, the goal of surgical repair is generally to reapproximate the ends of the injured nerve. Sometimes during repair after a nerve injury, a portion of the injured nerve, called a neuroma, needs to be excised, leaving a gap. When the nerve ends cannot be brought together, then a nerve graft may be necessary.

Nerve grafts are generally portions of a sensory nerve that are harvested from another part of the body to be used as graft material. Once the graft is in place, the regenerating nerve fibers grow from the proximal nerve stump, through the graft, through the distal nerve segment into the target muscles. Thus, patients may recover function in muscles following graft repair of nerve injuries. Sural nerve, superficial radial sensory, and medial antebrachial cutaneous nerve are common donor nerves for graft material.

Classification of nerve injury was described by Seddon in 1943 and by Sunderland in 1951 [41, 45]. The lowest degree of nerve injury in which the nerve remains intact but signaling ability is damaged is called neurapraxia. The second degree in which the axon is damaged but the surrounding connecting tissue remains intact is called axonotmesis. The last degree in which both the axon and connective tissue are damaged is called neurotmesis. Sunderland in 1951 reclassified nerve injury in detail related more to the anatomy of the nerve (Table 27.1).

It is well known that any degree of tension at the suture site may decrease the possibility of nerve healing; the tension diminishes the extrinsic vascular supply and predisposes to failure of the repair by increasing scar formation between the nerve stumps.

To bridge the nerve defects, the interfascicular autologous nerve grafting technique is still considered the “gold standard” but many other different “grafts” have been studied and described to avoid, in particular circumstances and in short nerve gaps, the use of autologous nerves (to avoid donor site morbidity).

Techniques reported below are applied in different situations; different indications can justify to avoid classical nerve graft: kind of nerves (mixed, pure), level and kind (“dominant” hemipulp in sensory nerves in the hand), kind of injury (in emergency (neat/blunt), late reconstruction). The aim of the reconstruction should be the one with the maximum of the results with the minimum harm for the patients. In this small review, we report only the clinical use of these grafts.

Loss of contractility of skeletal muscles and other target organ changes are a major concern in peripheral nerve surgery. Time interval between denervation and reinnervation is a critical determinant of functional outcome. Slow pace of axonal regrowth and immediate changes taking place in target tissues following peripheral nerve injuries make fully satisfactory clinical results unlikely. Repair or reconstruction of peripheral nerve lesions at very proximal levels such as brachial or lumbosacral plexus injuries, results in negligible return of function in extremities. Lessening denervation-reinnervation interval may decrease target tissue changes, and may lead to a better outcome. The concept of transferring healthy peripheral nerves to the distal segments of the proximally injured nerves at a level closer to target tissues is not new, but gaining acceptance only recently. Earlier and pioneering reports on peripheral nerve transfers from healthy muscles to denervated muscles, or from healthy skin to denervated skin indicated favorable outcomes [2, 29, 50–52]. During the last couple of years, exploding number of laboratory and clinical studies with promising clinical outcomes has been reported [48]. Currently, refinement of previously described procedures continues while newer innovative nerve transfers are described.