Peripheral nerve: trauma
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.
Presenting signs
- Trauma - including post-operative trauma after orthopedic surgery.
- Loss of function to sensory dermatomes and muscle supplied by affected nerve.
- Horner's syndrome Horner's syndrome in the cat may be due in some cases to trauma to vagosympathetic trunk and cervical ganglion in the neck area, particularly from cat bites.
Age predisposition
- Younger animals - trauma more common.
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.