Describe Peripheral Nerve Injuries in detail.

Definition & Importance

A peripheral nerve injury is damage to a nerve trunk that interrupts motor, sensory and autonomic conduction to the part it supplies. Nerves are commonly injured by laceration, traction, compression, ischaemia or as a complication of fractures and dislocations. Because a divided nerve regenerates slowly and imperfectly, early recognition and appropriate management are vital to preserve limb function.

Classification (seddon & Sunderland)

• Seddon described three grades.
• Neurapraxia — a temporary conduction block (e.g. From pressure) with the axon intact
• full recovery is expected in days to weeks.
• Axonotmesis — the axon is disrupted but the endoneurial sheath is intact
• Wallerian degeneration occurs distally but the axon can regrow along the preserved tube (~1 mm/day).
• Neurotmesis — complete division of the nerve (axon and sheath)
• spontaneous useful recovery is not possible and surgical repair is required. The Sunderland classification refines this into five degrees by the layer disrupted.

Seddon’s grades: neurapraxia (conduction block, recovers), axonotmesis (axon lost, sheath intact, regrows) and neurotmesis (complete division, needs repair).

Degeneration & Regeneration

After division, the distal segment undergoes Wallerian degeneration — the axon and myelin break down and are cleared by macrophages, leaving the endoneurial tubes (Schwann-cell columns). The proximal stump then sprouts axons that, if the tubes are intact and aligned, grow distally at about 1 mm per day to re-innervate the target. If the tubes are disrupted (neurotmesis) the sprouts may form a disorganised neuroma rather than reaching the end organ.

Clinical Features

There is motor loss (weakness/paralysis and, later, wasting of the supplied muscles), sensory loss in the nerve’s autonomous zone, autonomic changes (dry, warm then cold skin, loss of sweating) and loss of reflexes. A Tinel’s sign (tingling on percussion over the regenerating nerve front) that advances distally over time indicates recovery.

Investigations & Management

• Nerve conduction studies and EMG (performed after ~3 weeks) localise and grade the lesion and monitor recovery
• imaging (ultrasound/MRI) may show the nerve and any compressing lesion.
• Management depends on the type and cause.
• Closed injuries that are likely neurapraxia or axonotmesis are managed expectantly with splintage, physiotherapy to prevent contractures, and monitoring for recovery (advancing Tinel’s, EMG). A clean-cut (sharp) division is treated by primary microsurgical repair
• a contaminated or ragged wound is repaired secondarily once healed. A gap is bridged with a nerve graft (e.g. Sural nerve). Late/irrecoverable palsies are treated by tendon transfers to restore function.

• Seddon: neurapraxia (block, recovers), axonotmesis (axon lost/sheath intact, regrows), neurotmesis (division, repair).
• Wallerian degeneration distally; regeneration ~1 mm/day if tubes intact; neuroma if not.
• Motor, sensory, autonomic loss; advancing Tinel’s sign signals recovery.
• NCS/EMG at ~3 weeks localise and monitor; closed likely neurapraxia/axonotmesis → observe.
• Sharp division → primary repair; gap → nerve graft; irrecoverable → tendon transfer.