ELECTROMYOGRAPHY - DNB Orthopaedics MS Orthopedics MRCS Exam GUIDE - Orthodnb.com

DNB Orthopaedics  MS Orthopedics  MRCS Exam GUIDE - Orthodnb.com

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Monday 11 June 2018



Image result for electromyography
  • graphic recording of electrical activity of a muscle at rest and action
  • using electromyograph and recorded to electromyogram
  • detect the electrical potential generated by muscle cell when these cells contract and at rest
Normal muscle
  • at rest shows no electrical activity – voluntary contracture – action potential develops in motor unit
  • single motor unit potential – weak contraction
  • strong contraction – number of motor units fire simultaneously – superimposed to give – interference pattern
Denervated muscle
  • spontaneous electrical activity at rest – denervated potential
  • after 15-20 days of muscle denervation
Types of EMG needles used
  • concentric
  • monopolar
  • single fiber
  • macro electrode
Three types of activity recorded in EMG
  1. Insertional activity
  • brief action potential – only few seconds – stops immediately when needle movement stops
  • decreased in fibrosis or fat tissue replacement
  • prolonged in early denervation (irritability), myotonic disorders
  1. Spontaneous activity
  • monophasic (end plate noise) or biphasic ( end plate spikes)
  • when needle near a motor end plate
  • very short duration
  1. Voluntary activity
  • action potentials from Type I muscle fibers followed by strong ones from Type II fibers
  • interference pattern
  • prolonged in myopathy
  • shortened in neuropathy
  • peripheral neuropathy evaluation
  • identifying predominant pathophysiology : axonal/ demylinating, sensory/ motor, acute/sub acute/chronic
  • localizing level of lesion ( myelopathic, neuropathic, myopathic)
  • objective and qualitative measure of nerve function
Normal results
  • muscles at rest – electrically inactive
  • after the electrical activity of needle insertion – no abnormal spontaneous activity detected
  • voluntary contraction – action potential begin to develop
  • strength of contraction increases – more and more fibers produce action potentials
  • fully contracted – disorderly group of action potentials of varying rates and amplitudes
  • normal insertional activity – silent rest activity – no biphasic or triphasic potentials – not interference
Axonotmesis / Neuronotmesis
  • increased insertional activity – fibrillation and positive sharp waves in rest – no biphasic, triphasic, interference potentials
Demyelinating neuropathy
  • normal insertional and silent rest activity – no bi and triphasic – incomplete interference potential
  • abnormal clotting factors, anticoagulant therapy
  • extreme swelling
  • dermatitis, blood transmittable disorders
  • recent MI, pacemakers
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