Classification of Peripheral Nerve Injury

Original Editor - Tomer Yona 

Top Contributors - Emma Sewell, Kaylee Byars, Kathrine Baca

Description

Peripheral nerves are responsible for somatic (voluntary) and autonomic (involuntary) functions. The primary functions of the peripheral nervous system are to receive general sensations (touch, pressure, temperature, and pain), and special sensations (sight, smell, taste, and hearing), integrate sensory input from the entire body, and generate a response. Peripheral Nerve Injury can be sustained from traumatic or idiopathic mechanisms. Individuals with diagnoses of diabetes, alcoholism, vascular disease, autoimmune diseases, or who have been exposed to chemotherapy drugs or infections that attack nerves have a higher likelihood of acquired peripheral neuropathy. The severity of peripheral nerve injury is determined with advanced imaging (CT, MRI, or MRI neurography) or nerve conduction velocity testing and classified using the Sunderland classification system.  Treatment of peripheral nerve damage depends on the severity of the damage and may include surgical procedures, skilled physical therapy, orthotics, or medications .

Mechanism of Injury for Peripheral Nerves

The three most common mechanisms of injury for peripheral nerves are stretch related, lacerations, and compressions. The most common of these three is  stretch-related, followed by lacerations, and then compression.

Stretch Related

Due to the elastic nature of peripheral nerves, stretch related injuries can occur if a traction force is too strong for the nerves elasticity. If the traction force exceeds the nerves stretch abilities, a complete tear could occur. However, it is more common that the continuity of the nerve is retained during this type of injury.

Lacerations

Laceration injuries are the second most common types of peripheral nerve injuries. With this mechanism of injury, a nerve is severed partially or fully by some type of sharp object. Most common lacerations are from knives, broken glass, metal shards etc.

Compressions

Compression nerve injuries typically affect large-caliber nerves that cross over bony structures or between rigid surfaces. Acute compression (e.g. Saturday Night Palsey) and chronic compression injuries (e.g. carpal tunnel syndrome) are the two main subcategories for compression injuries. Compressive nerve injuries can result in complete functional loss of both motor and sensory function even though the nerve fibers are still intact. Two pathological mechanisms have been thought to contribute to these types of injuries: mechanical compression and ischemia. Mechanical compression could result in secondary ischemia issues which can compromise nerve microcirculation.

Classification

There are two commonly used classifications for PNI-  the Seddon Classification and the Sunderland Classification.

Seddon classified nerve injuries into three major groups: neurapraxia, axonotmesis, and neurotmesis whereas Sunderland expanded Seddon's Classification to five degrees of peripheral nerve injury as described in the table below:  

Seddon	Process	Symptoms	Sunderland
Neurapraxia	This type of nerve injury is usually secondary to compression pathology. This is the mildest form of peripheral nerve injury with minimal structural damage. This allows for a complete and relatively short recovery period. In a neuropraxic injury, a focal segment of the nerve is demyelinated at the site of injury with no injury or disruption to the axon or its surroundings. This is usually due to prolonged ischemia from excess pressure or stretching of the nerve with no Wallerian degeneration .	pain no muscle wasting muscle weakness numbness proprioception issues	First degree
Axonotmesis	An axonotmesis injury involves damage to the axon and its myelin sheath. However, the endoneurium, perineurium, and epineurium remain intact. Although the internal structure is preserved, the damage of the axons does lead to Wallerian degeneration () This type of nerve injury also results in a complete recovery although it does take longer than a neuropraxic injury.	pain muscle wasting complete motor, sensory, and sympathetic function loss	Second & Third degree
Neurotmesis	A neurotmesis injury can occur at different levels and thus Sunderland’s further breakdown into degrees of injury is useful. Disruption of the axon and endoneurium is considered a 3rd-degree injury, disruption of the axon and perineurium is a 4th degree, and a complete disruption of the nerve is classified as a 5th-degree injury. It is important to note that there is a slight overlap when looking at these nerve pathologies and these degrees of injuries are specific to the patient’s injury. Symptoms seen with a neurotmesis injury include no pain (anesthesia), muscle wasting, and complete motor, sensory, and sympathetic function loss ()	no pain (anesthesia) muscle wasting complete motor, sensory, and sympathetic unction loss	Third, Fourth, & Fifth Degree

  See Nerve Injury Rehabilitation Physiotherapy for more information regarding Physiotherapy treatment.