ISSN 2398-2993      

Sciatic injury

obovis

Synonym(s): Peripheral neuropathy, Nerve damage/trauma


Introduction

  • Cause: traumatic from calving, intramuscular (IM) injection,  ischemic myopathy, compression from abscess, neoplasia, or fractured sacrum, pelvis or proximal femur and associated inflammation/fibrosis.
  • Signs: those associated with LMN dysfunction including pain, paresis, paralysis, muscle atrophy, hyporeflexia and analgesia in severe cases.
  • Diagnosis: history and clinical signs plus the ruling out of other causes.
  • Treatment: analgesia, nursing and physiotherapy. 
  • Prognosis: variable.

Anatomy

  • The sciatic nerve is the largest nerve in the body. It is formed by fibers originating from spinal cord segments L6-S2. 
  • The fibers emerge together at the sciatic foramen as the large, wide, flat sciatic nerve (approx. 4cm wide and 0.5cm thick).
  • It is consistent in size and shape as is progresses caudally towards the coxo-femoral joint which it wraps behind as it changes direction, down the hind limb. At this point the sciatic nerve becomes more rounded before splitting into the tibial and common fibular branches .
    • Common fibular (peroneal) nerve – runs down anterior part of leg giving this area sensation and controlling hock flexion and digit extension
    • Tibial Nerve – runs down the posterior part of leg giving this area sensation and controlling hock extension and digit flexion.

Pathogenesis

Etiology

  • Interruption of nerve to target muscle(s) leading to decreased or absent function of target muscle(s).
    • Damage to the sciatic nerve will present as variable grades of proprioceptive dysfunction and loss of sensation.
    • Pelvic/spinal or femoral fracture associated with a fall or estrous activity.
    • Dystocia Dystocia resulting in nerve root damage within the pelvic cavity.
    • Damage caused by extra or intrafascicular (worse) injection following IM injection or subsequent sequelae eg abscess.
    • Ischaemic myopathy following recumbency (compartment syndrome).
    • Nerve entrapment by abnormal tissue secondary to fractures, injections or neoplasia.
    • Damage can be bilateral.

Predisposing factors

Specific

  • Thin cows and calves more at risk from (incorrect) needle placement during intra muscular injection .
  • All risk factors for dystocia Dystocia.
  • Unsympathetic handling.
  • Concrete flooring (tends to be slippery).

Pathophysiology

  • Peripheral nerve injuries can be classified according to the severity of damage to the neuron:
    • Neurapraxia:
      • The most mild type of injury, is an interruption of the conductive function of the nerve without physical damage to the axon. Most commonly caused by a disruption in blood supply, blunt trauma, or compression/entrapment. Recovery is usually spontaneous and complete occurring within 1-3 weeks.
    • Axonotmesis:
      • Is a physical interruption of the axon where it separates from the cell body but the endoneurium and myelin sheath remain intact. This results in Wallerian-like axonal degeneration and loss of impulse conduction distal to the injury. Recovery depends on successful regrowth of axons at approximately 1mm/day. 
    • Neurotmesis:
      • Refers to the complete severance of a nerve and its supporting structures, followed by Wallerian degeneration. Recovery is unlikely without surgical intervention.

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.
  • Kirkwood R M, Remnant J G, Paine R M, Murphy A M, Wapenaar W (2017) Risk of iatrogenic damage to the sciatic nerve in dairy cattle. Vet Rec 182, 140.
  • Rees G (2016) Postpartum emergencies in cows. In Practice 38, 23-31 VetMedResource.
  • Crilly J P, Rzechorzek N, Scott P (2015) Diagnosing limb paresis and paralysis in sheep. In Practice 37, 490-507 PubMed.
  • Divers T  J (2004) Acquired spinal cord and peripheral nerve disease. Vet Clin North Am Food Anim Pract 20 (2), 231-242 VetMedResource.

Other sources of information

  • de Lahunta A, Glass E, Kent, M (2015) Lower Motor Neuron: Spinal Nerve General Somatic Efferent System. In: Veterinary Neuroanatomy and Clinical Neurology, Fourth Edition. Elsevier Saunders, USA. pp 150-151.
  • Añor S (2013) Monoparesis. In: BSAVA Manual of Canine and Feline Neurology, Fourth Edition. Eds: Platt S R, Olby N J. British Small Animal Veterinary Association, UK. pp 265-279.
  • Scott P R, Penny C D & MacRae A I (2011) Nervous System Disorders. In: Cattle Medicine. Manson Publishing, UK. pp 160-161.
  • Weaver A D (2008) Lameness Above the Foot. In: Bovine Medicine: Diseases and Husbandry of Cattle. 2nd ednEds: Andrews A H,  Blowey R W, Boyd H, Eddy R G . Blackwell Science, UK. pp 438-448.
  • Greenough P R & Weaver A D (1997) Lameness in Cattle. 3rd edn. W B Saunders, USA. pp 210-211.

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