Traumatic and entrapment neuropathies
- Lesion
Nerves can be cut, stretched or squeezed. A cut nerve may regrow or form a painful tangle; a squeezed nerve at a tunnel causes numbness and weakness.
What it is
Physical injury to nerves includes laceration, stretch and avulsion, compression and entrapment. The severity is graded from neurapraxia (focal demyelination with an intact axon, recovering in weeks), through axonotmesis (axon divided, sheaths intact, good regrowth) to neurotmesis (whole nerve divided, regrowth needs surgical repair). When regenerating sprouts cannot find the distal stump, they form a traumatic neuroma, a painful tangle of axons and scar. Entrapment neuropathies arise where nerves pass through tight anatomic tunnels, such as the median nerve in the carpal tunnel. Morton neuroma is perineural fibrosis of a plantar digital nerve.
Structure
- Compression: focal demyelination under the pressure point, with tapering of myelin (paranodal intussusception) and axonal loss if prolonged.
- Traumatic neuroma: nodule of haphazard small nerve fascicles in dense collagen.
- Morton neuroma: thickened nerve with dense perineurial and endoneurial fibrosis, hyalinized arteries and mucoid change.
- Regeneration: clusters of small thinly myelinated axons.
Step by step
- Pressure or stretch first disrupts myelin and blood flow, causing a reversible conduction block.
- Prolonged or stronger force divides axons, which degenerate distally.
- Schwann cells proliferate and form tubes; the proximal stump sends out many sprouts.
- If the endoneurial tubes are intact, sprouts reach their targets and function returns.
- If the nerve is completely divided and not repaired, sprouts tangle in scar and form a painful neuroma.
Clinical notes
- Carpal tunnel: night tingling of the thumb, index and middle fingers, positive Phalen and Tinel tests, thenar wasting late.
- Common fibular palsy after leg crossing or a tight cast: foot drop with sensory loss on the dorsum of the foot.
- Nerve conduction studies localize the lesion and grade its severity.
Test yourself
Think of the answer, then tap the question to see it.
What is neurapraxia?
Focal conduction block from demyelination with an intact axon; it recovers in weeks.
What is a traumatic neuroma?
A disorganized mass of regenerating axons, Schwann cells and scar at the end of a cut nerve.
Which conditions predispose to carpal tunnel syndrome?
Pregnancy, hypothyroidism, acromegaly, rheumatoid arthritis, diabetes, amyloidosis and repetitive wrist use.
Is Morton neuroma a true neoplasm?
No. It is perineural fibrosis of a plantar digital nerve from repeated compression.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Carpal Tunnel Syndrome (StatPearls (NCBI Bookshelf), 2025); Ulnar Neuropathy (StatPearls (NCBI Bookshelf), 2025); Morton Neuroma (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.