Electromyography
*CY*
used for locating motor nerves
map with electrical stimulation
responds to mechanical activation
end point for techniques; MEP, motor mapping
No muscle relaxants/No paralysis/Controlled paralysis
Nothing that will constrain EMG
Nerve Conduction Velocity
stimulate exposed nerve, record from the same nerve at different sites
useful for locating conduction block; partial injury, neuroma in continuity
aids in decision to excise and graft or reanastamose vs. neurolysis
Unaffected by anesthetic agents
used for locating motor nerves
map with electrical stimulation
responds to mechanical activation
end point for techniques; MEP, motor mapping
No muscle relaxants/No paralysis/Controlled paralysis
Nothing that will constrain EMG
Nerve Conduction Velocity
stimulate exposed nerve, record from the same nerve at different sites
useful for locating conduction block; partial injury, neuroma in continuity
aids in decision to excise and graft or reanastamose vs. neurolysis
Unaffected by anesthetic agents
*LH*
Spontaneous EMG; result of surgical irritation or injury of the motor nerve fibers, muscles innervated by the injured roots will be activated, useful for monitoring nerve root irritation, does not detect ischemia, requires the patient to be unrelaxed during monitoring
EMG vs SSEP
EMG; sensitive to single nerve root irritations, real-time feedback, amount of activity does not predict clinical outcome, no NMB, cannot detect ischemic changes
SSEP; not sensitive to single nerve root irritations; requires averaging; change is predictive of outcome; not effected by NMB, detects ischemia
Evoked EMG; muscle response (compound muscle action potential - CMAP) from delivered stimulation of the nerve root; can be used to determine presence of motor neurons in the vicinity; used to confirm accuracy of pedicle screw placement, requires NMB not to be used
*criteria or stimulating mentioned before
EMG applications; tethered cord releases, cauda equina monitoring during intradural tumor removal, lumber decompression, cervical decompression, pedicle screw testing
Where do we record from?
Lumbar Adductor Longus L2-4; Vastus Lateralis L2-4; Peroneus Longus L5-S2; Biceps Femoris L5-S2; Anterior Tibialis L4-S1; Gastrocnemius S1-S2; Anal Sphincter (S2-S4)
Can we monitor thoracic EMG? yes, intercostal muscles T2-T6, rectus abdominous T6-T12, external obliques T6-T12
Muscles of the upper leg, muscles of the lower leg
Muscles of the upper arm, muscles of the lower arm
Muscles of the foot, muscles of the foot
Normal EMG Baseline
Types of EMG; spike train, neurotonic discharge, burst, random irregular, sustained activity
Noise vs EMG; electrical noise conducts immediately to all recording sites, noise arrives synchronously at all recording sites; EMG conducts at 40-60 m/sec EMG arrives at different times in different channels
Train of Four used to measure level of NMB, stimulate a peripheral nerve, record from a muscle innervated by the nerve, 4 muscle twitches are measured, the 4th twitch is compared to the 1st and must be greater than 50% of twitch 1 to be counted
Pedicle screw testing; bone is an insulator, the more bone there is, the more current required to activate the nerve root on the other side of the bone which in turn activates the muscle innervated by the nerve, acceptable placement of pedicle screws can be assessed based upon the amount of current required to activate a nerve root; direct nerve root activation occurs from 0.2 to 5 mA, pathologic nerve root thresholds may be higher, thresholds lower than 8mA may be suggestive of a pedicle wall breach
triggered EMG response
stimulation technique; anode (+) is placed in the flesh near the screw locations; cathode (-) is used to stimulate the screw; current is increased until there is a CMAP and then brought down just until the response disappears; threshold is the current at which the response just disappeared
Caution; it is important to recognize that current can shunt in the surgical field if the field becomes saturated; the screws should not have any blood or irrigation pooling around them; current shunting can raise the pedicle screw threshold to an abnormally high level; pedicle screw stimulation should not occur once rods have been put in to place
Spontaneous EMG; result of surgical irritation or injury of the motor nerve fibers, muscles innervated by the injured roots will be activated, useful for monitoring nerve root irritation, does not detect ischemia, requires the patient to be unrelaxed during monitoring
EMG vs SSEP
EMG; sensitive to single nerve root irritations, real-time feedback, amount of activity does not predict clinical outcome, no NMB, cannot detect ischemic changes
SSEP; not sensitive to single nerve root irritations; requires averaging; change is predictive of outcome; not effected by NMB, detects ischemia
Evoked EMG; muscle response (compound muscle action potential - CMAP) from delivered stimulation of the nerve root; can be used to determine presence of motor neurons in the vicinity; used to confirm accuracy of pedicle screw placement, requires NMB not to be used
*criteria or stimulating mentioned before
EMG applications; tethered cord releases, cauda equina monitoring during intradural tumor removal, lumber decompression, cervical decompression, pedicle screw testing
Where do we record from?
Lumbar Adductor Longus L2-4; Vastus Lateralis L2-4; Peroneus Longus L5-S2; Biceps Femoris L5-S2; Anterior Tibialis L4-S1; Gastrocnemius S1-S2; Anal Sphincter (S2-S4)
Can we monitor thoracic EMG? yes, intercostal muscles T2-T6, rectus abdominous T6-T12, external obliques T6-T12
Muscles of the upper leg, muscles of the lower leg
Muscles of the upper arm, muscles of the lower arm
Muscles of the foot, muscles of the foot
Normal EMG Baseline
Types of EMG; spike train, neurotonic discharge, burst, random irregular, sustained activity
Noise vs EMG; electrical noise conducts immediately to all recording sites, noise arrives synchronously at all recording sites; EMG conducts at 40-60 m/sec EMG arrives at different times in different channels
Train of Four used to measure level of NMB, stimulate a peripheral nerve, record from a muscle innervated by the nerve, 4 muscle twitches are measured, the 4th twitch is compared to the 1st and must be greater than 50% of twitch 1 to be counted
Pedicle screw testing; bone is an insulator, the more bone there is, the more current required to activate the nerve root on the other side of the bone which in turn activates the muscle innervated by the nerve, acceptable placement of pedicle screws can be assessed based upon the amount of current required to activate a nerve root; direct nerve root activation occurs from 0.2 to 5 mA, pathologic nerve root thresholds may be higher, thresholds lower than 8mA may be suggestive of a pedicle wall breach
triggered EMG response
stimulation technique; anode (+) is placed in the flesh near the screw locations; cathode (-) is used to stimulate the screw; current is increased until there is a CMAP and then brought down just until the response disappears; threshold is the current at which the response just disappeared
Caution; it is important to recognize that current can shunt in the surgical field if the field becomes saturated; the screws should not have any blood or irrigation pooling around them; current shunting can raise the pedicle screw threshold to an abnormally high level; pedicle screw stimulation should not occur once rods have been put in to place