Neurosurgery notes/Procedures/Cranial procedures/Neurophysiology/Motor and sensory monitoring in spinal surgery

Motor and sensory monitoring in spinal surgery

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Neurophysiology
  • For spinal surgery ‘multimodal’ monitoring is best practice
      • Motor
      • TCMEPS
      • Direct stimulation of corticospinal tracts
      • Direct waves (D waves):
        • Direct propagation of the stimulus along the corticospinal tract generates
        • Cannot be done for T10/11 lesions as not enough spinal cord to place the electrodes
        • Do not move the pad after it is placed as the baseline amplitude will be different if it is moved.
        • For continuous intraoperative monitoring during spinal surgery
          • Continuous because no movement occurs in the muscle.
          • No movement occurs because uses a single pulse rather than a train of 5 pulse.
        • Method
            • TCMEP, Stimulation of motor cortex
              • But here uses a single transcranial stimuli
            • Signal travel down spinal cord
            • One electrode is placed above the lesion to act as a control
            • One electrode is placed below the lesion to detect any changes
            Incision Of the Dorsal Median Raphe Posterior Tibial Nerve SEPs Right Left Ill IV 100 ms Removal Of the Tumor Muscle MEPs Right TA Left TA D -VVave 50 11 0. 4.6 110 uv ms
        • Pathology
          • If intraop loses the TCMEPs but D waves still present you can still carry on with surgery because
            • TCMEPs uses Corticospinal tracts and also secondary pathways (interneurons) to generate signal
            • D waves uses corticospinal tracts
              • Likely patient will have transient loss of power
                  • МусАо1оаву ДвзсС1»са Муевотяу оагдт et al 1997
          • If intraop lose 50% of D wave amplitude
            • Stop surgery as patient will likely have paralysis
      Somatosensory
      • SSEP
      EMG
      • Free running
      • Stimulated EMG.
  • Used during
    • Scoliosis surgery
      • Pedicle screws insertion may risk breaching the pedicle wall.
        • If the screw track is close to the nerve roots, stimulation applied along this track or through the inserted screw can generate a muscle twitch from the stimulated root, or lower segmental levels if the breach is medial and cord is stimulated.
        • Monitoring requires reliable stimulation, and reliable muscle recording.
        • The muscle must be innervated from the tested root and nerve and muscle must function.
    • Intramedullary tumours
    • Extramedullary tumours
    • Simple decompressive surgery
    • Conus tumours and cauda equina surgery can be complex.
      • In complex spinal lipoma surgery neurophysiology is a essential
  • Concentric stimulating probe
    • 10/ sec stimuli,
    • 0.3– 3 mA for roots, or up to 2 mA on the cord.
  • In addition, peroneal and posterior tibial SSEP recording, multiple muscles for EMG and MEP, particularly including sphincters, which are also used for the bulbocavernosus reflex monitoring
  • Difficult recording in
    • Obese patients
      • Muscle cannot be easily accessed with the paired recording needles.
    • Thoracic levels.