Axonotmesis

Excerpt

Peripheral nerve injuries (PNIs) are a relatively uncommon but potentially devastating health concern. As an illustration of patient dissatisfaction with such injuries, litigation following these common procedures, spine surgery, foot/ankle surgery, and arthroplasty is most often for PNI. PNI may result from traumatic or nontraumatic means and can often be iatrogenic in nature. Early identification of injury is of paramount importance as the best neurological outcomes are associated with early intervention.

Axonotmesis is a term that describes the range of PNIs that are more severe than a minor insult, such as those resulting in neurapraxia, yet less severe than the transection of the nerve, as observed in neurotmesis. Ultimately, these terms are used to describe gradations of nerve trunk involvement with a common underlying molecular process. However, the descriptive terms used to categorize the degree of damage to nerve structures permits the practitioner to consider different mechanisms, tailored therapeutic strategies, and appropriate expectations for functional outcomes.

In order to understand each grade of nerve injury, it is important to be familiar with the basic anatomy of the peripheral nerve. From most superficial to the deepest structures, the peripheral nerve contains epineurium, epifascicular epineurium intervening between fascicles, perineurium covering individual fascicles, endoneurium envelops axons that are wrapped by a myelin sheath and Schwann cells.

Sunderland and Dellon elaborated on Seddon's proposed gradations of PNI.

1. Grade I is considered neurapraxia. Histological changes may encompass focal segmental demyelination.

2. Grades II-IV are considered axonotmesis.

3. Grade II - intact endometrium; damaged axons

4. Grade III - intact perineurium; damaged axons and endoneurium

5. Grade IV - intact epineurium; damaged axons, endoneurium, and perineurium

6. Grades V is considered neurotmesis, which is a complete nerve transection.

7. Grade VI - multifocal mixed injury of the nerve. This is likely the most common type of injury.