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Peripheral nerve: trauma

ffelis

Synonym(s): Traumatic neuropathy


Introduction

  • Most common neuropathy.
  • Cause: accidental, eg mechanical blow, hit by a car HBCs (RTAs), gunshot wounds, fractures, pressure and stretching; iatrogenic, eg crushing, cutting or spiking the nerve during surgery (especially orthopedic procedures); compression by casts, splints or other dressings; injection into or adjacent to nerve.
  • Signs: depend on severity of injury; range from temporary loss of function to complete loss of function and muscle atrophy.
  • Treatment: surgery, physiotherapy.
  • Prognosis: good to poor depending on severity of injury.

Pathogenesis

Etiology

  • Accident - gunshot wounds, RTA, mechanical blow, fracture, pressure, ischemia.
  • Iatrogenic - cutting, crushing, spiking; compression by dressings, casts or splints; injections into or adjacent to nerve.
  • Intramedullary femoral pinning procedures have a notably higher incidence of iatrogenic nerve injuries than pinning procedures in other bones.

Predisposing factors

General

  • Access to outdoors (increased risk of trauma, eg HBC (RTA)).
  • Orthopedic procedure.
  • Intramuscular injections.

Pathophysiology

  • Mild trauma   →   temporary conduction block   →   physiological disruption of axonal function   →   no structural damage to axon.
  • More severe trauma   →   transection of axon (axotomy)   →   degeneration of distal axon divorced from cell body   →   impulses traveling down proximal stump no longer innervate muscle (motor) or receptor (sensory):
    • Motor disruption   →   loss of muscle function (paresis/paralysis), hypotonia, flaccidity.
    • Sensory disruption   →   anesthesia or dysthesia.

First degree injury

  • No structural damage, loss of function - neuropraxia.

Second degree injury

  • Axotomy, but basal lamina intact - axonotmesis.
  • Loss of function to sensory dermatomes and muscle supplied by affected nerve.

Third degree injury

  • Axotomy with disruption of basal lamina; perineurium/epineurium intact - neurotmesis I.
  • Epineurial and perineurial scarring at site of injury may impede regeneration.

Fourth degree injury

  • Axotomy with basal lamina, perineurial and epineurial disruption (ie transection) - neurotmesis II.
  • Epineurial and perineurial scarring at site of injury most likely in this form of injury - may impede regeneration.
  • Delayed regeneration may fail to fully restore function because of fibrosis/degeneration of target sites.

Timecourse

  • Neurological deficits immediately after injury.
  • Onset of muscle atrophy and nerve degeneration after 7-10 days.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Van Soens I, Struys M M, Polis I E et al (2009) Magnetic stimulation of the radial nerve in dogs and cats with brachial plexus trauma: a report of 53 cases. Vet J 182 (1), 108-113 PubMed.
  • Steinberg H S (1988) Brachial plexus injuries and dysfunctions. Vet Clin N Am 18 (3), 565-80 PubMed.
  • Thomas P K (1988) Clinical aspects of PNS regeneration. Advances Neurol 47, 9-29 PubMed.
  • Fanton J W, Blass C E, Withrow S J (1983) Sciatic nerve injury as a complication of intramedullary pin fixation of femoral fractures. JAAHA 19 (5), 687-94 VetMedResource.

Other sources of information

  • Swain S F (1987) Peripheral nerve surgery. In: Veterinary Neurology. Eds Oliver, Horlein and Mayhew. WB Saunders.

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