Nerve Injuries in Orthopaedics — MRCS Quick Reference

🔌 Nerve Injuries in Orthopaedics

Classification, upper limb nerve deficits, lower limb nerve deficits, the ulnar paradox, and surgical approach nerve risks.

Seddon & Sunderland Classification

Two systems are used in clinical practice. Seddon’s (1943) is the bedside standard with three grades. Sunderland’s (1951) expands the severe end into five grades for greater surgical precision. They map onto each other directly — know both.

Neuropraxia

Conduction block — no structural damage

Sunderland Grade I — “the concussion” — a dazed wire, not a broken one

Axon intact Endoneurium intact Perineurium intact Epineurium intact

Temporary biochemical/demyelination block. Motor > sensory loss. Autonomic preserved. Full spontaneous recovery — hours to 8 weeks. No Wallerian degeneration. Cause: compression (Saturday night palsy, tourniquet).

Prognosis

Excellent — full recovery

Axonotmesis

Axon disrupted — Schwann tube intact

Sunderland Grade II — “broken wire, intact tube” — axon dies distally but regenerates perfectly

Axon broken Myelin disrupted Endoneurium intact Perineurium intact Epineurium intact

Wallerian degeneration distal to injury over ~6 weeks. Regenerating axons guided by intact endoneurial tubes at 1 mm/day. Tinel’s sign advances distally as regeneration proceeds. No surgery needed — full recovery expected.

Prognosis

Good — recovery possible

III

Neurotmesis

Complete disruption — surgical repair needed

Sunderland Grades III–V — endoneurium/perineurium/epineurium progressively destroyed

Axon broken Endoneurium broken Perineurium broken (IV–V) Epineurium broken (V)

Grade III — endoneurial tubes destroyed; perineurium intact. Axons misdirect → partial, synkinetic recovery.
Grade IV — perineurium also disrupted. Nerve in continuity but non-functional neuroma.
Grade V — complete transection. No spontaneous recovery. Requires surgical repair (epineural suture, fascicular repair, or nerve graft).

Prognosis

Poor without surgery

Quick Comparison

Feature	Neuropraxia (I)	Axonotmesis (II)	Neurotmesis (III–V)
Axon	Intact	Disrupted	Disrupted
Endoneurium	Intact	Intact	Destroyed (III+)
Wallerian degeneration	No	Yes	Yes
Tinel’s sign advances	No	Yes	No (static)
Recovery	Full, hours–8 weeks	Full, 1 mm/day	Incomplete / none
Surgery needed	No	No	Yes (III–V)
Example cause	Tourniquet, compression	Traction, crush	Laceration, severe traction

The 1 mm/Day Rule — Calculating Expected Recovery

In axonotmesis, axons regenerate at approximately 1 mm per day (roughly 1 inch per month). To estimate recovery time: measure the distance from the injury site to the target muscle in millimetres, then divide by 30 to get months. Add a few weeks for the initial delay before regeneration begins. Tinel’s sign advancing distally at this rate confirms regeneration is occurring — a static Tinel’s suggests the nerve is blocked (neuroma) and surgical exploration may be needed.

Sunderland’s Refinement of Neurotmesis

The MRCS often tests knowledge of all five Sunderland grades. The key progression:
Grade III — axon + endoneurium gone; perineurium intact → nerve holds together, partial recovery possible
Grade IV — axon + endoneurium + perineurium gone; epineurium intact → nerve in continuity but functionally dead (neuroma-in-continuity)
Grade V — all layers transected → complete loss, no spontaneous recovery, surgical repair essential

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