Nerve Injury Classification

Nerve Injury Classification

Identifying degrees of nerve injury dates to terminology devised by Sir Herbert Seddon in his work as a surgeon dealing with traumatic open wounds suffered in World War II. A mild/moderate/severe surgical model was chosen in posterity to label a completely severed nerve (needing surgery) neurotmesis, and one that recovered without treatment neuropraxia. He later wrote that use of the term neuropraxia was “unfortunate”.Seddon labeled an intermediate level of injury axonotmesis. He characterized axonotmesis as pathology involving axon and myelin, leaving the rest of the nerve intact. A description of firm pressure onto a nerve with a watchmaker’s forceps, breaking the axon and myelin, leaving the nerve stroma in continuity is offered.Sir Syndey Sunderland in 1951 modified Seddon’s surgical model with an anatomic one. This neatly identified graded nerve pathology based on the anatomic nerve structures. This is sort of an “inside to out’ model. His grade V corresponded to Seddon’s neurotmesis; grade I described neuropraxia.Contemporary surgeons Susan E Mackinnon and A. Lee Dellon have chosen pragmatically to identify a 6th degree nerve injury, describing the fact that a nerve may have varying degrees of pathology. They use the term “neuroma in continuity, and explain that the pattern of recovery will be mixed.

A summary of Seddon’s surgical model and Sunderland’s anatomic model is shown below.

 

 

Classification of Nerve Injuries

Degree of Injury

myelin axon endoneurium perineurium epineurium
I; Neuropraxia +/-
II; Axonotmesis yes yes no no no
III yes yes yes no no
IV yes yes yes yes no
V; Neurotmesis yes yes yes yes yes
VI (Mackinnon/Dellon)   various fibers/fascicles, mixed pathologic changenervecrosssection

 

 

 

 

 

 

 

 

 

 

With all due respect to Drs Seddon and Sunderland, reconciling electrophysiologic data with surgical and anatomic models is problematic.** We seldom are dealing with open traumatic wounds or nerves that are pinched with a watchmaker’s forceps. All completely severed nerves will produce unevokable (no response) motor and sensory action potentials with NCS. However, not every “no response” observed means that the nerve has been severed. In some instances (radial neuropathy-spiral groove with mid humeral fracture), recovery is predictable and orderly. In other instances, unevokable responses (severe carpal tunnel syndrome) need surgical intervention.In addition, the models described by Seddon and Sunderland do not address varying degrees of pathology noted involving sensory and motor fibers. In general, (carpal tunnel syndrome), mild/early pathology seems to affect sensory NCS before motor changes.In general, depending on the nerve, degree of pathology identified via EMG/NCS escalates from sensory to motor NCS change, to EMG changes. A sensory response will usually become unevokable in the presence of a still involved, but evokable motor response. Abnormal motor and sensory NCS can describe pathology in the presence of a normal EMG.When describing a nerve injury an attempt should be made to identify the degree of sensory NCS, motor NCS and EMG changes noted. At that point, treatment is predicated on historic knowledge of how other similar cases have responded. Mid humeral fracture with radial neuropathy usually respond, even though the nerve appears “neurotmetic” distal to the triceps brachii. Median neuropathy at the wrist with unevokable motor/sensory responses and complete thenar denervation may improve in a fourteen year old suffering a distal radius fracture. The same data in 55-year-old woman may be an indication for surgery.**Dr. Jun Kimura has attempted to utilize terms described by Seddon based on the chronology of nerve degeneration following an injury. He describes NCS within the first four days following a nerve injury. NCS results in an unevokable response with stimulation proximal to the lesion site. At that point in time, it is not known if the terms neuropraxia, axonotmesis, or neurotmesis may be used.

If a nerve has been severed, the nerve segment distal to the lesion remains electrically viable for the first 4-7 days. Evaluation of that segment will remain normal during that period of time, even though the nerve is severed. During the 2nd week, if responses are unevokable, the term neurotmesis may be invoked. Axonotmesis will produce a reduced response, neuropraxia normal response.

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Ray Jurewicz
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E-mail: rj@NerveStudy.com Web Site design by Larry Berman and Chris Maher

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