Peripheral nerve injury: an update

Abstract

Peripheral nerves convey signals between the spinal cord and the rest of the body. Peripheral nerve injury (PNI) is a challenging problem with a variety of aetiologies and symptoms. Injuries can be classified into three categories: neurapraxia, axonotmesis and neurotmesis. Axonotmesis and neurotmesis result in Wallerian degeneration of the axons distal to the site of injury. After this process is complete, damaged neurons attempt to regenerate the damaged fibre with axonal budding. Successful axonal growth relies on an intact connective tissue tunnel and the requisite signalling molecules to allow the axon to re-grow in the correct direction and re-innervate the target tissue. Without this, the axons may form a painful neuroma. To differentiate between the different grades of nerve injury special tests can be utilized including neurophysiological investigation–nerve conduction studies and electromyography (EMG). Imaging the damaged nerve with ultrasound or MRI may be useful for diagnosis and surgical planning, however investigations should not delay referral to a nerve surgeon. The aim of surgical repair in nerve injury is to re-establish continuity between the connective tissue structures of the nerve; this allows axons to elongate across the site of injury to reach the target tissue. The simplest technique is tensionless end-to-end epineural repair. In injuries where this is impossible other surgical options include nerve grafting, nerve conduits or nerve transfer.