The Peripheral Nerve: Neuroanatomical Principles Before and After Injury

Abstract

The major component of a peripheral nerve is the connective tissue for surrounding the nerve fibres and their axons and Schwann cells. This connective tissue protects all these elements and provides their nutrition. A nerve fascicle contains a lot of nerve fibres that are covered by the perineurium. Inside of the perineurium, another connective tissue is located, like the endoneurium. The connective tissue covering the whole nerve is termed epineurium, and it continues between the fascicle as interfascicular epineurium. The gliding connective tissue around the nerve is called the paraneurium.

Peripheral nerves receive blood supply from small vessels leading to the epineurium, perineurium and endoneurium (intrinsic vessels). The extrinsic blood supply is delivered by segmentally arranged vessels originating from neighbouring vessels.

Nerve injuries were characterized according to Seddon in neurapraxia, axonotmesis and neurotmesis. Meanwhile a new classification into five grades according to Sunderland is used. The latter classification is based on the histological features of nerve structures after the injury.

Peripheral nerves have a regenerative potential after injury. An antegrade nerve degeneration is named Wallerian degeneration, and this process is completed after several weeks. Whenever the injury does not lead to neuronal death, a functional restoration is possible. In cases of severe damage, a nerve reconstruction is indicated. A regenerating axon grows through a scar with an average 1.0–8.5 mm per day. Mechanical factors as well as the time between trauma and nerve repair, the type of nerve injured, the level of injury and associated injuries are very important for a good functional recovery.