Radial nerve: trauma in Horses (Equis) | Vetlexicon
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Radial nerve: trauma

ISSN 2398-2977

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Introduction

  • Cause: humeral fractures or post-anesthetic recumbency.
  • Signs: non-weightbearing, lack of elbow extension, inability to fix elbow, resting of elbow in extended position, resting the dorsum of pastern on the ground, forward thrust of the limb at walk.
  • Diagnosis: thoracic limb lameness.
  • Treatment: DMSO, corticosteroids, surgery.
  • Prognosis: good to grave.

Presenting signs

  • Non-weightbearing on the affected limb.
  • With pure radial nerve paralysis the horse will be able to bear weight if limb is splinted.
  • With pure radial nerve paralysis horse is unable to "fix" elbow and carpus. This is why they appear non-weightbearing.
  • Elbow rested in the flexed position with the dorsum of the pastern on the ground "dropped elbow".
  • At a walk, the limb will be thrust forward.

Geographic incidence

  • Worldwide.

Pathogenesis

Etiology

  • Humeral fractures.
  • Collisions with objects.
  • Post-recumbency anesthesia   →   especially if the limb is malpositioned and stretched.

Pathophysiology

  • Largest outflow from brachial plexus.
  • Innervates extensors of elbow, carpus and digit.
  • Sensory component to front of antebrachium.
  • Depending on site of the injury the paralysis can be total or partial.
  • Probably caused by compression of the radial nerve roots between the scapula and the ribs.
  • Not commonly damaged alone.
  • Involvement with humeral fractures possible.

Timecourse

  • Long-standing damage   →   atrophy of triceps brachialis, extensor carpi radialis, ulnaris lateralis and the digital extensor muscles.

Diagnosis

Presenting problems

  • Forelimb lameness.

Client history

  • Trauma.
  • Limb fracture.
  • Recent procedures that require general anesthesia.

Clinical signs

  • Non-weightbearing of the affected leg.
  • Lack of elbow extension.
  • Inability of fixation of elbow.
  • Resting of elbow in extended position "dropped elbow".
  • Resting the dorsum of pastern on the ground   Forelimb: radial nerve paralysis  .
  • Forward thrust of the limb at walk.
  • Measurement of the affected limb circumference using a measurement tape can be helpful in picking up subtle decreases in limb diameter associated with muscle atrophy.

Diagnostic investigation

Other
  • Neurologic examination  Neurology: examination - adult    Neurology: examination - foal  .
  • Electrodiagnostic aids(EMG and nerve conduction velocity) may be helpful in diagnosing diseases of the nerves   →   because the muscle is the end organ of the peripheral nerve, damage to the nerve can lead to abnormal muscle electrical potentials such as positive sharp waves and fibrillation potentials.
  • Muscle biopsymay reveal muscle fiber atrophy, angular fibers, and fiber type grouping characteristics of denervation.

Confirmation of diagnosis

Discriminatory diagnostic features

  • History and clinical signs.

Definitive diagnostic features

  • Neurologic examination .

Treatment

Standard treatment

Medical management
  • Dimethyl sulfoxide (DMSO)  Dimethyl sulfoxide  :
    • Can be used in horses with acute injury to peripheral nerves.
    • Its principal action is to scavenge free oxygen radicals generated in damaged tissue.
    • Helps to maintain blood flow to hypoxic tissues by reducing generation of prostaglandins and thromboxane, thus preventing platelet aggregation
    • Can be efficacious early in the onset of peripheral nerve trauma both intravenously (IV) (1 g/kg as a 10% solution) and topically over the affected area.
  • Corticosteroids:
    • Can be efficacious in acute peripheral nerve trauma.
    • Dexamethasone   Dexamethasone  (0.05-0.2 mg/kg IV) may be used initially.
    • Short-term administration of corticosteroids is best, but long-term administration may be necessary.

    When given at the recommended doses, corticosteroids can act synergistically with DMSO
    Surgical management
  • May not be necessary in uncomplicated nerve injury if the horse is not used for performance.
  • If the nerve is severed, then it should be anastomosed at the time of injury.

Subsequent management

Treatment

Surgical management
  • Surgical exploration of the area to free entrapped nerves or hematomas should only be performed if the condition persists.
  • Removal of adhesions, neuromat, and possible re-anastomosis can be performed 2-8 weeks after injury.
    Physical therapy
  • May be effective in developing compensatory mechanisms and strength in horses that have recovered from the initial nerve injury.
  • Horses may improve dramatically with regular and controlled exercise on a lunge line, treadmill, or at pasture.
  • Exercise allows the unaffected parts of the nervous system to compensate for the affected muscles by increasing strength and conscious proprioception.
  • Massage, therapeutic ultrasound   Musculoskeletal: therapeutic ultrasound  , ice packs, and hydrotherapy of affected muscle groups for 10-15 min, two to three times daily should be carried out.
  • Passive flexion and extension of the affected limb are also helpful in maintaining range of motion.
  • Splinting of affected limbs may keep the limb from dragging on the ground, thus preventing ulcer formation or secondary muscle contracture.

Prevention

Outcomes

Prognosis

  • Some cases improve dramatically in 2-4 weeks (neurapraxia).
  • Few cases progressively improve over 6-18 months with physiotherapy such as swimming exercise.
  • Even with degrees of residual triceps atrophy, some horses have returned to full performance and even gallop and race successfully.
  • Grave, if nerve regrowth of more than 12 in (30 cm) is required for recovery.

Reasons for treatment failure

  • Fibrotic contracture of the muscles is a common complication of prolonged recovery.

Further Reading

Publications

Refereed papers