AAEM MINIMONOGRAPH 28 ABSTRACT: This article reviews the epidemiology and classification of traumatic peripheral nerve injuries, the effects of these injuries on nerve and muscle, and how electrodiagnosis is used to help classify the injury. Mecha- nisms of recovery are also reviewed. Motor and sensory nerve conduction studies, needle electromyography, and other electrophysiological methods are particularly useful for localizing peripheral nerve injuries, detecting and quantifying the degree of axon loss, and contributing toward treatment de- cisions as well as prognostication. © 2000 American Association of Electrodiagnostic Medicine. Published by John Wiley & Sons, Inc. Muscle Nerve 23: 863–873, 2000 TRAUMATIC INJURY TO PERIPHERAL NERVES LAWRENCE R. ROBINSON, MD Department of Rehabilitation Medicine, University of Washington, Seattle, Washington 98195 USA EPIDEMIOLOGY OF PERIPHERAL NERVE TRAUMA company central nervous system trauma, not only Traumatic injury to peripheral nerves results in con- compounding the disability, but making recognition siderable disability across the world. In peacetime, of the peripheral nerve lesion problematic. Of pa- peripheral nerve injuries commonly result from tients with peripheral nerve injuries, about 60% have 30 trauma due to motor vehicle accidents and less com- a traumatic brain injury. Conversely, of those with monly from penetrating trauma, falls, and industrial traumatic brain injury admitted to rehabilitation accidents. Of all patients admitted to Level I trauma units, 10 to 34% have associated peripheral nerve 7,14,39 centers, it is estimated that roughly 2 to 3% have injuries. It is often easy to miss peripheral nerve peripheral nerve injuries.30,36 If plexus and root in- injuries in the setting of central nervous system juries are also included, the incidence is about 5%.30 trauma. Because the neurological history and exami- In the upper limb, the nerve most commonly re- nation is limited, early hints to a superimposed pe- ported injured is the radial nerve, followed by ulnar ripheral nerve lesion might be only flaccidity, are- and median nerves.30,36 Lower limb peripheral nerve flexia, and reduced movement of a limb. injuries are less common, with the sciatic most fre- Peripheral nerve injuries are of significant im- quently injured, followed by peroneal and rarely port as they impede recovery of function and return tibial or femoral nerves. Fractures of nearby bones to work and carry risk of secondary disabilities from are commonly associated, such as humeral fractures falls, fractures, or other secondary injuries. An un- with radial neuropathy. derstanding of the classification, pathophysiology, In wartime, peripheral nerve trauma is much and electrodiagnosis of these lesions is critical to the more common, and much of the knowledge about appropriate diagnosis, localization, and manage- peripheral nerve injury, repair, and recovery comes ment of peripheral nerve trauma. from experience derived in the American Civil War, World Wars I and II, and subsequent wars.20,35,40 CLASSIFICATION OF NERVE INJURIES Peripheral nerve injuries may be seen as an iso- For the purposes of this article, trauma is defined as lated nervous system injury but may also often ac- injury resulting from kinetic energy applied to the nerve or limb. This includes, for example, the ki- Abbreviations: CMAP, compound muscle action potential; EMG, elec- netic energy of the patient moving at high speed into tromyography; MUAP, motor unit action potential; NCS, nerve conduction a car or wall, a bullet moving through tissue with a study; SNAP, sensory nerve action potential Key words: electromyography; peripheral nerve; trauma high velocity, or a sudden stretch of a limb. Kinetic Correspondence to: American Association of Electrodiagnostic Medi- energy (KE) is proportional to the mass of the object cine, 421 First Avenue SW, Suite 300 East, Rochester, MN 55902; e-mail [email protected] (m) and the square of the velocity (v): © 2000 American Association of Electrodiagnostic Medicine. Published 2 by John Wiley & Sons, Inc. KE=½mv. AAEM MM#28: Nerve Injury MUSCLE & NERVE June 2000 863 Thus, a doubling of the velocity (e.g., bullet velocity rium) remains partially or fully intact. Wallerian de- or motor vehicle speed) results in a fourfold increase generation occurs, but subsequent axonal regrowth in kinetic energy applied to the body or body part. may proceed along the intact endoneurial tubes. Re- Knife or other sharp wounds are also included in this covery ultimately depends upon the degree of inter- review, though the amount of kinetic energy neces- nal disorganization in the nerve as well as the dis- sary for a significant peripheral nerve injury is prob- tance to the end organ. Sunderland’s classification ably lower. Although burns and electrical injuries (see below) further divides this category. Neurotme- also derive from high amounts of energy (thermal or sis describes a nerve that has been either completely electrical) applied to tissue, these injuries will not be severed or is so markedly disorganized by scar tissue considered here because the pathophysiology of the that axonal regrowth is impossible. Examples are injury is significantly different from those wounds sharp injury, some traction injuries, and percussion resulting from kinetic energy. injuries, or injection of noxious drugs. Prognosis for There are two predominant schemes that have spontaneous recovery is extremely poor without sur- been proposed for classification of peripheral nerve gical intervention. traumatic injuries: that of Seddon35 and that of Sun- Sunderland40 uses a more subdivided scheme to derland40 (Table 1). The former is more commonly describe peripheral nerve injuries, with five groups used in the literature. Seddon has used the terms instead of three. First-degree injury represents con- “neurapraxia,” “axonotmesis,” and “neurotmesis” to duction block with completely intact stroma and cor- describe peripheral nerve injuries.35 Neurapraxia is responds to Seddon’s classification of neurapraxia. a comparatively mild injury with motor and sensory Prognosis is good. Second-degree injury involves loss but no evidence of Wallerian degeneration. The transection of the axon but with completely intact nerve distally conducts normally. Focal demyelin- endoneurium and stroma. Recovery can occur by ation and/or ischemia are thought to be the etiolo- axonal regrowth along endoneurial tubes. Third- gies of the conduction block. Recovery may occur degree injury represents transection of the axon and within hours, days, weeks, or up to a few months. endoneurial tubes, but the surrounding perineu- Axonotmesis is commonly seen in crush injuries, rium is intact. Recovery depends upon how well the nerve stretch injuries (such as from motor vehicle axons can cross the site of the lesion and find endo- accidents and falls), or percussion injuries (such as neurial tubes. Fourth degree injury involves loss of from gunshot wounds). The axons and their myelin continuity of axons, endoneurial tubes, and perineu- sheaths are broken, yet the surrounding stroma (i.e., rium. Individual nerve fascicles are transected, and the Schwann tubes, endoneurium, and perineu- the continuity of the nerve trunk is maintained only Table 1. Classification systems for nerve injury.* Seddon Sunderland classification classification Pathology Prognosis Neurapraxia First degree Myelin injury or ischemia Excellent recovery in weeks to months Axonotmesis Axon loss Good to poor, depending upon integrity of Variable stromal disruption supporting structures and distance to muscle Second degree Axon loss Good, depending upon distance to muscle Endoneurial tubes intact Perineurium intact Epineurium intact Third degree Axon loss Poor Endoneurial tubes disrupted Axonal misdirection Perineurium intact Surgery may be required Epineurium intact Fourth degree Axon loss Poor Endoneurial tubes disrupted Axonal misdirection Perineurium disrupted Surgery usually required Epineurium intact Neurotmesis Fifth degree Axon loss No spontaneous recovery Endoneurial tubes severed Surgery required Perineurium severed Prognosis after surgery guarded Epineurium severed *Adapted from Dillingham.8 864 AAEM MM#28: Nerve Injury MUSCLE & NERVE June 2000 by the surrounding epineurium. Traction injuries results in block of conduction rather than simply commonly produce these types of lesions. Prognosis severe slowing. is usually poor without surgical intervention because There are relatively few changes in muscle as a of the marked internal disorganization of guiding result of neurapraxic lesions. Disuse atrophy can oc- connective tissue elements and associated scarring. cur when neurapraxia is more than transient. There Fifth-degree injury describes transection of the en- remains debate as to whether muscle fibrillates after tire nerve trunk and is similar to Seddon’s neurot- a purely neurapraxic lesion (see below). mesis. Some authors have described another degree of EFFECTS OF AXONOTMESIS ON NERVE injury, known as sixth-degree injury.25 This is a AND MUSCLE mixed lesion with both axon loss and conduction Soon after an axonal lesion, the process of Wallerian block occurring in some fibers. This type of lesion is degeneration starts to occur in nerve fibers. This probably quite common and requires skillful electro- process is well described elsewhere10,27 and will be diagnostic data collection and analysis to separate it only briefly reviewed here. There are changes in from pure axon-loss lesions. both the