A 19-year-old sustains a deep laceration to the medial aspect of his forearm from broken glass. On examination, he has weakness of finger flexion and reduced sensation over the little finger. The wound was surgically explored and the ulnar nerve was found to be fully transected.
What type of nerve injury is this, and what is the management?
Why Classification Matters
Peripheral nerve injuries range from a nerve that is simply "stunned" and will recover fully within days, to one that is completely severed and will never recover without surgery. Getting the classification right isn't academic — it directly determines whether you counsel a patient to wait, arrange nerve conduction studies, or book theatre. Two classification systems are used side by side: Seddon's (simpler, three categories) and Sunderland's (more detailed, five degrees, useful for planning surgery).
Seddon Classification — The Three Categories
| Type | Pathology | Prognosis |
|---|---|---|
| Neurapraxia | Local myelin damage (e.g. compression), axon continuity preserved — a "conduction block" | Full recovery, typically days to 12 weeks |
| Axonotmesis | Axon disrupted but the surrounding connective tissue (endoneurium) stays intact, providing a tube for regrowth | Recovers spontaneously — regeneration at ~1mm/day along the preserved tube |
| Neurotmesis | Complete disruption of the nerve including its connective tissue — the two ends have no guide to regrow toward | No spontaneous recovery — surgical repair required |
Sunderland extends Seddon's axonotmesis category into three separate degrees (2nd, 3rd, 4th) depending on how many of the internal connective tissue layers (endoneurium, perineurium, epineurium) are damaged — this matters because it predicts how well spontaneous regeneration will actually restore function, even when the nerve tube is technically intact. A 4th-degree injury may need surgery even though it isn't a full transection.
The Key Clinical Question: Explore or Wait?
The single most important decision in peripheral nerve injury is whether to explore surgically now, or observe for spontaneous recovery. This depends heavily on the mechanism of injury.
Mechanism Predicts Management
- Sharp/clean laceration (glass, knife): High suspicion of neurotmesis — explore and repair early, ideally within 72 hours, since the cut ends are easy to identify and align before scarring sets in
- Blunt/traction/crush injury (fracture, dislocation, stretch): Often neurapraxia or axonotmesis even if the deficit looks severe — a period of observation (typically 6–12 weeks) with serial exams and nerve conduction studies is usually appropriate before considering surgery
- Gunshot/high-velocity injury: Even without direct nerve transection, the surrounding blast effect can cause significant axonotmesis — generally observed initially unless there's a clean transection
- No improvement by 3 months in a closed/blunt injury expected to recover spontaneously: nerve conduction studies and surgical referral for consideration of exploration and grafting
Tinel's sign — tingling elicited by tapping over the course of a recovering nerve — can be used to track regeneration. As the nerve regrows, the point of maximal tingling should progressively move distally over successive visits, roughly matching the expected ~1mm/day regeneration rate. A Tinel's sign that isn't advancing suggests regeneration has stalled and merits re-evaluation.
Principles of Surgical Repair
When repair is indicated, several principles guide the approach:
Surgical Decision-Making
- Primary end-to-end repair: preferred when the nerve ends can be approximated without tension, usually possible for clean lacerations repaired early
- Nerve grafting: needed when there is a gap that cannot be closed without tension — typically using a sensory donor nerve (e.g. sural nerve)
- Timing: earlier repair generally gives better outcomes — motor endplates and Schwann cell "readiness" to support regrowth decline over time, so delayed repair (beyond ~6 months) has progressively worse functional outcomes
- Physiotherapy and splinting throughout, to prevent joint contracture while awaiting reinnervation
This was a clean, sharp laceration with complete ulnar nerve transection confirmed at exploration — a clear neurotmesis. Primary end-to-end epineural repair was performed under microscope within 24 hours of injury, with the wound edges approximated tension-free. He was followed with serial Tinel's sign testing, which advanced steadily distally over the following months, and regained protective sensation and partial motor function by 8 months post-repair.
Seddon: neurapraxia (best) → axonotmesis → neurotmesis (needs surgery). Sunderland subdivides axonotmesis into three degrees. Sharp lacerations = explore early; blunt/traction injuries = observe first, typically 6–12 weeks. Track recovery with Tinel's sign and serial exams. Earlier repair gives better functional outcomes when surgery is needed.
References
- Seddon HJ. Three Types of Nerve Injury. Brain. 1943;66(4):237–288.
- Sunderland S. A Classification of Peripheral Nerve Injuries Producing Loss of Function. Brain. 1951;74(4):491–516.
- Kaya Y, Sarikcioglu L. Sir Herbert Seddon (1903–1977) and the Seddon Classification. Child's Nervous System. 2015;31(2):177–178.
