Peripheral Nerve Injuries Clinical Presentation

Updated: Dec 01, 2020
  • Author: Stefanos F Haddad, MD; Chief Editor: Murali Poduval, MBBS, MS, DNB  more...
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History and Physical Examination

The clinical appearance following nerve injury varies according to the nerve affected (sensory, motor, or combined). Injury to a motor nerve results in loss of muscle function, whereas injury to a sensory nerve results in loss of sensation to the affected nerve's sensory distribution, neuromatous or causalgia pain, or both. [1, 2]



Classification of nerve injury was described by Seddon in 1943 [7]  and by Sunderland in 1951. [8]  The classification of nerve injury described by Seddon comprised neurapraxia, axonotmesis, and neurotmesis. Sunderland expanded this classification system to include five degrees of nerve injury, as described below.

First-degree nerve injury

A first-degree injury or neurapraxia involves a temporary conduction block with demyelination of the nerve at the site of injury. Electrodiagnostic study results are normal above and below the level of injury, and no axonal degeneration or denervation muscle changes are present. No Tinel sign is present. Once the nerve has remyelinated at that area, complete motor and sensory recovery occurs. Recovery may take up to 12 weeks.

Second-degree nerve injury

A second-degree injury or axonotmesis results from a more severe trauma or compression. This causes wallerian degeneration distal to the level of injury and proximal axonal degeneration to at least the next node of Ranvier. In more severe traumatic injuries, the proximal degeneration may extend beyond the next node of Ranvier.

Electrodiagnostic studies of motor nerve injuries demonstrate denervation changes in the affected muscles, and in cases of reinnervation, motor unit potentials (MUPs) are present. Axonal regeneration occurs at the rate of 1 mm/day or 1 in./month and can be monitored with an advancing Tinel sign. The endoneurial tubes remain intact, and recovery therefore is complete, with axons reinnervating their original motor and sensory targets.

Third-degree injury

The third degree of injury was introduced by Sunderland to describe an injury more severe than second-degree injury. As with a second-degree injury, wallerian degeneration occurs, and electrodiagnostic studies demonstrate denervation changes with fibrillations in the affected muscles. In cases of reinnervation, MUPs are present.

Regeneration occurs at a rate of 1 mm/day, and progress may be monitored with an advancing Tinel sign. However, with the increased severity of the injury, the endoneurial tubes are not intact, and regenerating axons therefore may not reinnervate their original motor and sensory targets.

The recovery pattern is mixed and incomplete. Reinnervation of sensation occurs only if sensory fibers reach their sensory end organs; similarly, muscle reinnervation occurs if motor nerve fibers reach their muscle targets. Even within a sensory nerve, recovery can be mismatched if sensory fibers reinnervate a different area within the nerve's sensory distribution. If the muscle target is far from the injury site, nerve regeneration may occur, but the muscle may not be reinnervated, because of the long period of denervation and irreversible muscle degeneration.

Fourth-degree injury

A fourth-degree injury results in a large area of scar at the site of nerve injury and precludes any axons from advancing distal to the level of nerve injury. Electrodiagnostic studies reveal denervation changes in the affected muscles, and no MUPs are present. A Tinel sign is noted at the level of the injury, but it does not advance beyond that level. No improvement in function is noted, and surgery is required to excise the neuroma and restore neural continuity, thus permitting axonal regeneration and motor and sensory reinnervation.

Fifth-degree injury

A fifth-degree injury is a complete transection of the nerve. Like a fourth-degree injury, it requires surgery to restore neural continuity. Electrodiagnostic findings are the same as those for a fourth-degree injury.

Sixth-degree injury

The category of sixth-degree injury was introduced by Mackinnon to describe a mixed nerve injury that combines the other degrees of injury. [2] This type of injury commonly occurs when some fascicles of the nerve are working normally while other fascicles may be recovering, and other fascicles may require surgical intervention to permit axonal regeneration.