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Nerve Entrapment

- See:
       - Carpal Tunnel
       - Cervical Disc Disease
       - Cubital Tunnel Syndrome

- Nerve Entrapment:
    - w/ entrapment, nerve fibers are not affected uniformly;
    - superficially located fibers tend to bear the brunt of compression, while central fibers are relatively spared;
    - large diameter, heavily myelinated fibers are more sensitive to compression than poorly myelinated fibers;
    - thus fibers subserving light touch and motor fibers are more likely to be involved in compression neuropathy than unmyelinated pain fibers;

- Types of Compression:
    - mild and brief compression produces a transient conduction block in nerve, which normalizes soon after the pressure is relieved;
           - there are no major structural changes in the nerve, but axoplasmic flow is interrupted because extrinsic pressure;
    - w/ acute severe compression one observes a characteristic sequential invagination of telescoping of the myelin sheath;
    - chronic compression:
           - segmental demyelination occurs (axonotmesis)
           - this accounts for the slowing of the nerve observed clinically;
           - w/ sustained compression, axolysis occurs in compressed segment, and wallerian degernation occurs distally;
           - critical threshol pressure for initiating changes in nerve is 30 mm Hg
           - neuroma in continuity: (spindle neuroma - eg Morton's neuroma)
                    - in most cases nerve has an intact perineural sheath
                    - may result from chronic nerve compression and irritation which causes nerve swelling;
                    - the proliferation of fibrous tissue causes nerve compression;

- Electromyography
    - Motor Conduction Latency:
    - Sensory latency

Current Concepts: Entrapment Neuropathies of the Upper Extremities.