“Your doctor will need to determine the exact location and severity of the nerve injury. A classification system called the Sunderland Classification system divides nerve injuries into five parts. These include:

1. First-degree injury: A reversible local conduction block at the site of the injury. This injury does not require surgical intervention and usually will recover within a matter hours to a few weeks.

2. Second-degree injury: There is a loss of continuity of the axons or electrical wires within the nerve. If this kind of injury can be confirmed through pre-operative nerve testing, surgical intervention is usually not required.

3. Third-degree injury: There is damage to the axons and their supporting structures within the nerve. In this case, recovery is variable. Intra-operative nerve conduction studies are often able to help predict outcome and need for simple cleaning of the nerve (neurolysis) or a more extensive repair with grafting.

4. Fourth-degree injury: In this case, there is damage to the axons and the surrounding tissues sufficient to create scarring that prevents nerve regeneration. Intra-operative electrical testing confirms that no electrical energy can be passed along the neural pathways in this injured nerve. Surgical intervention with nerve grafting is necessary to repair the damage.

5. Fifth-degree injury: These injuries are usually found in laceration or severe stretch injuries. The nerve is divided into two. The only way to repair a fifth-degree injury is through surgery.”

http://www.hopkinsmedicine.org/neurology_neurosurgery/centers_clinics/peripheral_nerve_surgery/conditions/nerve_injury.html 

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