Nerve injury classification

Nerve injury classification assists in prognosis and determination of treatment strategy for nerve injuries. Classification was described by Seddon in 1943 and by Sunderland in 1951. In the lowest degree of nerve the nerve remains intact, but signaling ability is damaged, termed neurapraxia. In the second degree the axon is damaged, but the surrounding connecting tissue remains intact – axonotmesis. The last degree, in which both the axon and connective tissue are damaged, is called neurotmesis.

Seddon's classification
In 1943, Seddon described three basic types of nerve injury:

Neurapraxia (Class I)
Neurapraxia is a temporary interruption of conduction without loss of axonal continuity. Neurapraxia involves a physiologic block of nerve conduction in the affected axons.

Other characteristics:
 * mildest type of nerve injury
 * sensory-motor problems present distal to the site of injury
 * intact endoneurium, perineurium, and the epineurium
 * wallerian degeneration not present
 * intact conduction in the distal and proximal segments, but no conduction across the injury
 * full nerve conduction recovery, requiring days to weeks
 * fibrillation potentials (FP) lacking, and positive sharp EMG waves.

Axonotmesis (Class II)
Axonotmesis involves loss of relative axon continuity and myelin covering, but preservation of the connective tissue framework (including encapsulating tissue, the epineurium and perineurium).

Other characteristics:
 * distal Wallerian degeneration
 * distal sensory and motor deficits
 * nerve conduction distal to the site of injury (3 to 4 days after injury) absent
 * fibrillation potentials (FP), and positive, sharp EMG waves (2 to 3 weeks post injury).
 * axonal regeneration and recovery does not typically require surgical treatment, although surgical intervention may be required, due to scar tissue

Neurotmesis (Class III)
Neurotmesis is total severance/disruption of the nerve fiber. Axon, endo-, peri-, and epineurium transected. Neurotmesis may be partial or complete.

Other characteristics:
 * distal Wallerian degeneration
 * partial or complete connective tissue lesion
 * severe sensory-motor problems and autonomic function defect
 * nerve conduction distal to the site of injury absent (3 to 4 days after lesion)
 * no distal conduction (EMG and NCV (nerve conduction velocity)
 * surgical intervention is necessary to restore function

Sunderland's classification
In 1951, Sunderland expanded Seddon's classification to five degrees. The first two are the same as Seddon's.

Sunderland's third-degree and fourth-degree are included within Seddon's axonotmensis. Sunderland's third-degree is nerve fiber interruption. Includes an endoneurium lesion, with an intact epineurium and perineurium. Recovery from a third-degree injury may require surgical intervention. In fourth-degree injury, only the epineurium remain intact, requiring surgical repair.

Sunderland's fifth-degree is included within Seddon's neurotmesis. Fifth-degree lesion is a complete transection of the nerve, including the epineurium. Recovery requires appropriate surgical treatment.