Peripheral Nerve Injury Classification
On this page
Direct answer
Peripheral nerve injury is classified by Seddon into neurapraxia, axonotmesis and neurotmesis, according to whether the axon and its sheaths are intact, disrupted or transected. Neurapraxia is a conduction block that recovers fully within weeks, while neurotmesis is complete division that needs surgical repair. Sunderland's five grades refine the same spectrum and guide the decision between observation and operation.
What you must remember
- Neurapraxia (Seddon): local demyelination with the axon intact, causing a temporary conduction block that usually recovers fully within weeks.
- Axonotmesis: axonal disruption with the endoneurium, perineurium and epineurium preserved, so the nerve regenerates along its original tubes and recovers spontaneously.
- Neurotmesis: complete division of the nerve, with no spontaneous recovery, so surgical repair is needed.
- Sunderland grades: first degree is neurapraxia, second is axonotmesis, third involves the endoneurium, fourth involves the fascicles, and fifth is complete transection.
- Tinel sign: tingling elicited by tapping along the nerve, which marks the advancing front of regenerating axons.
- Regeneration rate: regrowth is slow, roughly around 1 mm a day as commonly quoted, so a long gap delays recovery considerably.
- Electrodiagnosis: denervation changes on electromyography appear after about two to three weeks, so early testing is often inconclusive.
Grading a nerve lesion step by step
The sequence matters because a nerve injury is often a waiting game, and the decision to explore depends on how the lesion evolves. The steps below follow the usual course.
- Document the deficit: record motor and sensory loss in the nerve's territory before any treatment, using the same examination each time.
- Assess the mechanism: a stretch or contusion suggests neurapraxia, while a sharp laceration suggests neurotmesis.
- Watch for recovery: review the patient every few weeks, looking for return of function and advance of a Tinel sign.
- Use electrophysiology: EMG and nerve conduction studies, performed after about two to three weeks, help separate a conduction block from axonal loss.
- Decide on exploration: a lesion without recovery by the expected time, or one with a sharp transection, prompts surgical exploration and repair.
- Protect the limb: splint the joints and prevent contracture, since a recovering nerve is worthless if the muscle is stiff.
| Classification | Axon | Sheaths | Recovery |
|---|---|---|---|
| Neurapraxia (Seddon) | Intact | Intact | Full, usually within weeks |
| Axonotmesis (Seddon) | Disrupted | Preserved | Spontaneous, along original tubes |
| Neurotmesis (Seddon) | Disrupted | Divided | Needs surgical repair |
The table shows that Seddon's scheme depends on what is preserved, while the Sunderland grades give finer detail on the internal structures. Both systems point to the same question: whether the lesion will recover without an operation.
Where the exam tries to catch you
Most lost marks come from confusing the grade with the mechanism or from operating too early on a conduction block.
- Trap: a nerve that stops working after a stretch injury must be explored at once. Correct: neurapraxia usually recovers in weeks, so observation is the usual course unless recovery fails.
- Trap: axonotmesis and neurotmesis are both treated with immediate repair. Correct: axonotmesis recovers spontaneously along the original tubes, while only neurotmesis needs surgical repair.
- Trap: a positive Tinel sign means the nerve has fully recovered. Correct: the Tinel sign marks the advancing front of regeneration, so it shows progress but not full function.
Frequently asked questions
What is the difference between neurapraxia and axonotmesis?
Neurapraxia is a conduction block with an intact axon, and it recovers fully within weeks. Axonotmesis disrupts the axon while the surrounding sheaths are preserved, so the nerve regenerates along its original tubes over time.
What is neurotmesis according to Seddon?
Neurotmesis is complete division of a peripheral nerve, with the axon and all its sheaths transected. It does not recover spontaneously and needs surgical repair, such as neurorrhaphy or grafting.
What does a Tinel sign indicate in nerve injury?
A Tinel sign is tingling felt when the nerve is tapped, and it marks the advancing front of regenerating axons. A Tinel sign moving distally over time shows that regeneration is progressing.
How are Sunderland grades different from Seddon classification?
Sunderland describes five grades, from first-degree neurapraxia to fifth-degree complete transection, based on the internal structures involved. Seddon uses three broad categories, so Sunderland gives finer detail on which layers are damaged.