it has a great developing technique that is used for fixation and fusion in spine surgery .
it was firstly introduced by harrington and tullos in 1969 and then in late 1980s developed by roy camille et al . , louis , and steffe .
it could be applied in degenerative , trauma , neoplastic , infectious and malformation cases that had a problem with axial instability . despite its usefullness ,
nerve root , spinal cord injury , vascular injury , cerebrospinal fluid leak , visceral injury , pedicle fracture were some complications that mostly related to pedicle screw malpositioning . among those complications ,
the nerve injury due to pedicle screw malpostioning was a common complication that was faced by spine surgeons , .
there were a various neurophysiologic techniques used to assess functional integrity of the nervous system during surgical procedures .
it was useful by providing real time evaluation and immediate feedback to the surgeon at a point where intervention with any doubt taken .
this real time feedback would be a guide for surgeon to determine the precise decision in preventing irreversible neural damage , .
once warning signal was recognized by ionm , surgeon had to make a precise decision to overcome that problem . establishing the cause , mechanism and
the pathology of injury associated with nerve injury during spinal surgery were mandatory tools to surgeon as consideration to make an appropriate decision . in this review , a case of nerve entrapment problem after screw insertion on thoracolumbar compression fracture that recognized by intraoperative neurophysiologic monitoring at ciptomangunkusumo hospital was presented and correct management was discussed . a 47  year old male fell from his motorcycle following a traffic accident eleven years ago during which he landed on the asphalt with his buttocks .
seven month before hospital admission , patient had the pain worse ( vas 45 ) , but he could still move his both leg .
mri examination showed a compression fracture at the level vertebrae thoracal t12 and lumbar l1 .
it showed also there was small fragment of bone come into the canal and compressed the anterior segment of spinal cord ( fig .
laboratory examination showed there is an increase in parameter of erythrocyte sedimentation rate ( 52  mm / h ) , c - reactive protein ( 50  mg / l ) and leucocyte count ( 12.200/l ) .
surgery was performed with general anesthesia and under continuous neurophysiology monitoring of mep ( motor evoked potentials ) , ssep ( somatosensory evoked potentials ) and free - running emg ( electromyography ) .
ssep of bilateral tibial nerves was performed with the stimulation at the ankle and scalp recording at cz - fz and c3-c4/c4-c3. mep was performed with stimulatioan at m3-m4 or m1-m2 ( best response ) with single train stimulation of 7 pulses with 200.000  hz frequency , 0.5  ms duration and 0100  ma intensity and recorded at abductor hallucis brevis muscle and tibialis anterior bilateral muscle .
free run emg was recorded with the settting of 50  uv / division gain and 100  ms / division sweep at rectus femoris muscle and tibialis anterior muscle bilateral to prevent radix iritation during instrumentation .
it was performed the facet joint release and posterior stabilization at the level vertebrae thoracal t11 , t12 and lumbar l2 , l3 .
intra - operative accident was happened when the operator inserted the pedicle screw at level left thoracal t12 .
the surgeon then decided to pullout the pedicle screw and change the location of pedicle insertion to one level above , vertebrae thoracal t11 ( fig .
after changing the screw position , ssep monitor showed that the nerve amplitude was corrected to the acceptable value ( fig .
final screw insertion was at t10 , t11 and l2 , l3 on both side .
post - operative evaluation showed that the pain was decreased ( vas 12 ) and there was no deficit in motoric and sensoric function ( fig .
a 47  year old male fell from his motorcycle following a traffic accident eleven years ago during which he landed on the asphalt with his buttocks .
seven month before hospital admission , patient had the pain worse ( vas 45 ) , but he could still move his both leg .
mri examination showed a compression fracture at the level vertebrae thoracal t12 and lumbar l1 .
it showed also there was small fragment of bone come into the canal and compressed the anterior segment of spinal cord ( fig .
laboratory examination showed there is an increase in parameter of erythrocyte sedimentation rate ( 52  mm / h ) , c - reactive protein ( 50  mg / l ) and leucocyte count ( 12.200/l ) .
surgery was performed with general anesthesia and under continuous neurophysiology monitoring of mep ( motor evoked potentials ) , ssep ( somatosensory evoked potentials ) and free - running emg ( electromyography ) .
ssep of bilateral tibial nerves was performed with the stimulation at the ankle and scalp recording at cz - fz and c3-c4/c4-c3. mep was performed with stimulatioan at m3-m4 or m1-m2 ( best response ) with single train stimulation of 7 pulses with 200.000  hz frequency , 0.5  ms duration and 0100  ma intensity and recorded at abductor hallucis brevis muscle and tibialis anterior bilateral muscle .
free run emg was recorded with the settting of 50  uv / division gain and 100  ms / division sweep at rectus femoris muscle and tibialis anterior muscle bilateral to prevent radix iritation during instrumentation .
it was performed the facet joint release and posterior stabilization at the level vertebrae thoracal t11 , t12 and lumbar l2 , l3 .
intra - operative accident was happened when the operator inserted the pedicle screw at level left thoracal t12 .
the surgeon then decided to pullout the pedicle screw and change the location of pedicle insertion to one level above , vertebrae thoracal t11 ( fig .
3 ) . after changing the screw position , ssep monitor showed that the nerve amplitude was corrected to the acceptable value ( fig .
final screw insertion was at t10 , t11 and l2 , l3 on both side .
post - operative evaluation showed that the pain was decreased ( vas 12 ) and there was no deficit in motoric and sensoric function ( fig .
iatrogenic spinal cord injury was still a feared complication especially in deformity correction surgery such as scoliosis ( idiopathic , congenital , neuromuscular , and related syndrome ) , exaggerated kyphosis , and lordosis . according to the scoliosis research society , the estimated incidence of neurological complications for such surgery was 1% , and it would increase to 1.87% when a combined surgical approach is used .
mechanisms that could have been responsible for neurologic injury during spine procedure were : ( a ) direct injury due to surgical trauma , especially during spinal canal decompression or placement of spinal implant ; ( b ) traction and/or compression affecting neural structure , that could be occured during spinal realignment and deformity correction using spinal instrumentation or as a result of epidural hematoma following corpectomy procedure ; ( c ) ischemia resulting in decreased perfusion of the spinal cord and/or nerve roots , resulting in ischemic injury to neurologic structures ( e.g. following ligation of critical segmental vessels supplying the spinal cord or after an episode of sustained hypotension ) .
ischemia was the most common mechanism that was responsible for neurologic deficit during scoliosis surgery ; ( d ) compressive neuropathy as a result of patient positioning prior to or during surgery ( e.g. brachial plexus injury ) .
the causes of iatrogenic neurologic sequelae were implant - related damage , such as breach of a pedicle screw into the spinal canal or foramen , and injury during correction maneuvers , including distraction , compressive force to correct deformity , and the rod rotation technique to realign the vertebra . but among those causes the implant related damage was most common in clinical practice .
the ideal pedicle screw should have a maximum diameter and length without breaching the pedicle s cortical layer , the vertebral body . and the direction of insertion should converge on both side of one vertebrae .
lonstein et al . , described that the most common type of perforation wass anterior cortex ( 2.8% ) , and followed by lateral cortex ( 1.0% ) , inferior cortex ( 0,6% ) , medial cortex of pedicle ( 0,4% ) and superior cortex ( 0,2% ) .
nevertheless , a satisfactory outcome could also be achieved despite sub - optimal screw placement and vice versa .
for example , a screw that just barely touches the lower border of the pedicle may cause a clinically apparent radiculopathy and it may require revision . on the other hand , a screw that lies inside the spinal canal may produce no symptoms at all .
therefore , the evaluation of successful fusion surgery should always include a clinical assessment in addition to an appraisal of screw position .
intraoperative neuromonitoring ( ionm ) was a technique that now widely accepted to reduce the risk of neurologic complications in spinal surgery .
various ionm modalities allowed con - tinuous functional assessment of the neuromuscular junction , peripheral nerves , spinal cord , brainstem , and cortex during spinal surgery . among the various ionm techniques available , somatosensory evoked potentials ( ssep ) , transcranial electric muscle evoked potentials ( tcemep ) , and spontaneous electromyography ( free  run emg ) were most frequently used in clinical practice .
a previous study reported that false negative ssep monitoring occurred during surgery in only 0.063% of patients .
a large multicenter study had reported that postoperative paraplegia was reduced more than 50%60% with ssep monitoring .
this was modification of the basic electroencephalography ( eeg ) in which a cortical or subcortical response to repetitive stimulation of a peripheral mixed nerve was recorded at sites cephalad and caudad to the operative field .
data including signal amplitude ( height ) and latency ( time of occurrence ) were recorded continuously during surgery and compared with baseline data .
ssep provided direct information about status of the ascending spinal cord sensory tracts ( located in the dorsal medial columns of the spinal cord ) .
there are some limitations such as : ( a ) ssep provided only indirect information about the status of the spinal cord motor tracts ( located in the anterolateral columns of the spinal cord ) ; ( b ) ssep data did not provide real - time data regarding neurologic function because there was a slight delay ( usually,1  min ) while the ssep response was averaged for extraction from background noise ; ( c ) sseps could be unrecordable in patients with severe myelopathy , peripheral neuropathy , or obesity .
in addition , recording ssep is not a sensitive technique for monitoring individual nerve root function ; ( d ) sseps recording can be disturbed by operating room power equipment ( due to electrical interference ) , halogenated anesthetic agents , nitrous oxide , hypothermia , and hypotension .
the surgeon should be notified when ssep showed a persistent unilateral or bilateral loss of amplitude 50% or greater relative to baseline amplitude .
changes in latency were common and less significant , and spinal cord injury was unlikely if amplitude is unchanged .
transcranial electric motor - evoked potentials ( tcemep ) were neuroelectric impulses elicited by transcranial application of a high - voltage stimulus to electrodes placed over specific scalp regions to excite specific areas of the motor cortex .
these descending impulses stimulated corticospinal tract axons and were typically recorded from electrodes placed over key upper and lower extremity peripheral muscles as a compound muscle action potential ( cmap ) .
motor - evoked potentials could also be recorded directly from the spinal cord ( d- and i - waves ) via electrodes placed percutaneously or through a laminotomy .
the tcemep could provide information about the functional integrity of the spinal cord motor tracts that could not be obtained using ssep .
they were extremely sensitive to alterations in spinal cord blood flow resulting from intraoperative hypotension or evolving vascular injury .
in addition , alterations in tcemep presented earlier than changes in ssep in patients with evolving neurologic injury , which permits earlier initiation of corrective action to prevent permanent neurologic compromise . the tcemep were not a replacement for ssep but were used in combination with ssep to provide a direct measure of both spinal cord sensory and motor tract function , thereby increasing the efficacy of spinal monitoring .
the surgeon should be notified when tcemep showed a persistent unilateral or bilateral loss of amplitude 65% or greater relative to baseline amplitude .
spontaneous or free - running electromyography ( emg ) was widely applied to monitor selective nerve root function during spinal cord surgery .
spontaneous emg could help to prevent postoperative radiculopathy during spinal instrumentation surgery , including pedicle screw placement .
this technique did not require stimulation and could be recorded continuously from preselected muscle groups based on the nerve roots at risk .
surgical manipulations such as pulling , stretching or compression of nerves provoked spikes or bursts of activity termed neurotonic discharges , resulting in activity in the corresponding innervated muscle(s ) .
spontaneous emg was quite sensitive to irritation of the nerve root , such as retraction of spinal cord or nerve root , saline irrigation and manipulation during surgery . however , false spontaneous emg activation commonly occured during irrigation with cold water , cauterization and use of a high - speed drill because it was sensitive to temperature change .
intraoperative triggered emg detected root irritation or the post injury condition of the root after medial pedicle breach .
an irritated or damaged nerve root caused a decrease in electric threshold followed by sudden appearance of cmap of the specific muscles of the myotome after stimulation via the screw .
each pedicle screw was electrically stimulated with an increasing intensity from 5 to 30  ma ( duration , 0.2  ms ; frequency , 0.8  hz ) .
recordings were made at the level of the lower limb muscles with or without the rectus abdominis muscles ( depending on the root levels to test ) .
the recording of muscle activity at an intensity under 10  ma ( the classically accepted threshold ) argued in favor of a medial breach ( close proximity of the screw to the nerve root ) .
although ionm generally referred to neurophysiological monitoring , the stagnara wakeup test , which provideed direct evaluation of the patient s motor functions without specialized equipment , was still used when necessary
. when neuromonitoring alert ( significant decrease or loss of neurophysiologic potentials ) occured during surgery , the surgeon and anesthesiologist should remain calm and communicate with the spinal monitoring personnel as the following steps are taken : ( a ) check that the electrodes had not become displaced ; ( b ) elevate and maintain the mean arterial blood pressure between 85 and 95  mmhg to prevent spinal cord ischemia ; ( c ) assess if there has been a change in anesthetic technique ; ( d ) reverse any antecedent surgical event ( e.g. strut graft / cage placement ; surgical maneuvers including distraction , compression , or translation ) ; ( e ) inspect for an obvious source of neural compression ( e.g. bone fragment , hematoma ) ; ( f ) elevate body temperature and irrigate the wound with warm saline ; ( g ) send an arterial blood gas and laboratory tests to assess for an unrecognized metabolic abnormality or unrecognized low hemoglobin ; ( h ) if the tcemep / ssep data failed to recover , a wake - up test and awake clinical examination are considered ; ( i ) depending on the patient s response to the wake - up test and the specific spinal problem undergoing treatment , spinal instrumentation may require removal .
the individual clinical scenario and stability of the spine must be considered in decision making ; ( j ) usage of steroids ( spinal injury protocol ) was an option .
acute trauma as a result of spine instrumentation may result in significant edema , with mass effect causing neurophysiological dysfunction .
immediate administration of an intravenous bolus of methylprednisolon , followed by constant infussion for following 2448  h , may help ameliorating the mass effect and improving the neurologic outcome .
we were still considered for the protocol of steroid injection because the protocol was still implemented and adopted in our hospital .
but we were not evaluated the benefit of the steroid injection related to the spinal cord injury .
the impact of longer segment stabilization for the thoracic area were less than the lumbar area . in order to keep away the longer segment stabilization risk
, we can strengthen the other side by adding one more rod with rod connector . by this technique
a previous study reported that false negative ssep monitoring occurred during surgery in only 0.063% of patients .
a large multicenter study had reported that postoperative paraplegia was reduced more than 50%60% with ssep monitoring .
this was modification of the basic electroencephalography ( eeg ) in which a cortical or subcortical response to repetitive stimulation of a peripheral mixed nerve was recorded at sites cephalad and caudad to the operative field .
data including signal amplitude ( height ) and latency ( time of occurrence ) were recorded continuously during surgery and compared with baseline data .
ssep provided direct information about status of the ascending spinal cord sensory tracts ( located in the dorsal medial columns of the spinal cord ) .
there are some limitations such as : ( a ) ssep provided only indirect information about the status of the spinal cord motor tracts ( located in the anterolateral columns of the spinal cord ) ; ( b ) ssep data did not provide real - time data regarding neurologic function because there was a slight delay ( usually,1  min ) while the ssep response was averaged for extraction from background noise ; ( c ) sseps could be unrecordable in patients with severe myelopathy , peripheral neuropathy , or obesity .
in addition , recording ssep is not a sensitive technique for monitoring individual nerve root function ; ( d ) sseps recording can be disturbed by operating room power equipment ( due to electrical interference ) , halogenated anesthetic agents , nitrous oxide , hypothermia , and hypotension .
the surgeon should be notified when ssep showed a persistent unilateral or bilateral loss of amplitude 50% or greater relative to baseline amplitude .
changes in latency were common and less significant , and spinal cord injury was unlikely if amplitude is unchanged .
transcranial electric motor - evoked potentials ( tcemep ) were neuroelectric impulses elicited by transcranial application of a high - voltage stimulus to electrodes placed over specific scalp regions to excite specific areas of the motor cortex .
these descending impulses stimulated corticospinal tract axons and were typically recorded from electrodes placed over key upper and lower extremity peripheral muscles as a compound muscle action potential ( cmap ) .
motor - evoked potentials could also be recorded directly from the spinal cord ( d- and i - waves ) via electrodes placed percutaneously or through a laminotomy .
the tcemep could provide information about the functional integrity of the spinal cord motor tracts that could not be obtained using ssep .
they were extremely sensitive to alterations in spinal cord blood flow resulting from intraoperative hypotension or evolving vascular injury .
in addition , alterations in tcemep presented earlier than changes in ssep in patients with evolving neurologic injury , which permits earlier initiation of corrective action to prevent permanent neurologic compromise . the tcemep were not a replacement for ssep but were used in combination with ssep to provide a direct measure of both spinal cord sensory and motor tract function , thereby increasing the efficacy of spinal monitoring .
the surgeon should be notified when tcemep showed a persistent unilateral or bilateral loss of amplitude 65% or greater relative to baseline amplitude .
spontaneous or free - running electromyography ( emg ) was widely applied to monitor selective nerve root function during spinal cord surgery .
spontaneous emg could help to prevent postoperative radiculopathy during spinal instrumentation surgery , including pedicle screw placement .
this technique did not require stimulation and could be recorded continuously from preselected muscle groups based on the nerve roots at risk .
surgical manipulations such as pulling , stretching or compression of nerves provoked spikes or bursts of activity termed neurotonic discharges , resulting in activity in the corresponding innervated muscle(s ) .
spontaneous emg was quite sensitive to irritation of the nerve root , such as retraction of spinal cord or nerve root , saline irrigation and manipulation during surgery
. however , false spontaneous emg activation commonly occured during irrigation with cold water , cauterization and use of a high - speed drill because it was sensitive to temperature change .
intraoperative triggered emg detected root irritation or the post injury condition of the root after medial pedicle breach . an irritated or damaged nerve root caused a decrease in electric threshold followed by sudden appearance of cmap of the specific muscles of the myotome after stimulation via the screw .
each pedicle screw was electrically stimulated with an increasing intensity from 5 to 30  ma ( duration , 0.2  ms ; frequency , 0.8  hz ) .
recordings were made at the level of the lower limb muscles with or without the rectus abdominis muscles ( depending on the root levels to test ) .
the recording of muscle activity at an intensity under 10  ma ( the classically accepted threshold ) argued in favor of a medial breach ( close proximity of the screw to the nerve root ) .
although ionm generally referred to neurophysiological monitoring , the stagnara wakeup test , which provideed direct evaluation of the patient s motor functions without specialized equipment , was still used when necessary
. when neuromonitoring alert ( significant decrease or loss of neurophysiologic potentials ) occured during surgery , the surgeon and anesthesiologist should remain calm and communicate with the spinal monitoring personnel as the following steps are taken : ( a ) check that the electrodes had not become displaced ; ( b ) elevate and maintain the mean arterial blood pressure between 85 and 95  mmhg to prevent spinal cord ischemia ; ( c ) assess if there has been a change in anesthetic technique ; ( d ) reverse any antecedent surgical event ( e.g. strut graft / cage placement ; surgical maneuvers including distraction , compression , or translation ) ; ( e ) inspect for an obvious source of neural compression ( e.g. bone fragment , hematoma ) ; ( f ) elevate body temperature and irrigate the wound with warm saline ; ( g ) send an arterial blood gas and laboratory tests to assess for an unrecognized metabolic abnormality or unrecognized low hemoglobin ; ( h ) if the tcemep / ssep data failed to recover , a wake - up test and awake clinical examination are considered ; ( i ) depending on the patient s response to the wake - up test and the specific spinal problem undergoing treatment , spinal instrumentation may require removal . the individual clinical scenario and stability of the spine must be considered in decision making ; ( j ) usage of steroids ( spinal injury protocol ) was an option .
acute trauma as a result of spine instrumentation may result in significant edema , with mass effect causing neurophysiological dysfunction
. immediate administration of an intravenous bolus of methylprednisolon , followed by constant infussion for following 2448  h , may help ameliorating the mass effect and improving the neurologic outcome .
we were still considered for the protocol of steroid injection because the protocol was still implemented and adopted in our hospital .
but we were not evaluated the benefit of the steroid injection related to the spinal cord injury .
the impact of longer segment stabilization for the thoracic area were less than the lumbar area . in order to keep away the longer segment stabilization risk
, we can strengthen the other side by adding one more rod with rod connector . by this technique
insertion of pedicle screw in spinal surgery had a risk of complication that could prevent by usage of intraoperative neurophysiological monitoring .
ssep , tcmep and free running emg could detect the neurophysiological reaction of the spinal cord , therefore preventing undesired neurological disturbance post - operatively .
the authors declare that there is no conflict of interests regarding the publication of this paper
 introductionintraoperative neurophysiologic monitoring ( ionm ) had important role related to the complications in spinal surgery . 
 somatosensory evoked potential ( ssep ) , transcranial electric muscle evoked potentials ( tcemeps ) , and free run emg are parameters used to asses functional integrity of the nervous system during surgical procedures . 
 once warning signal was recognized , surgeon have to make a precise decision to overcome that problem.presentation of casewe present a 47-year old male with back pain due to compression fracture of thoracic vertebra t12 and lumbar vertebrae l1 . 
 while stabilizing through the posterior approach on the t11 and 12 as well as l2 and l3 , the ssep monitor showed 50% reduction in the waveform as the pedicle screw was inserted at the left side of t12 . 
 the instrumentation was changed into vertebra thoracal t10 , t11 , and vertebrae lumbar l2 , l3 . 
 the ssep normalized and post operatively pain decreased . 
 after surgery there was no neurological deficit.discussionacute trauma as a result of spine instrumentation may provoke significant edema , with mass effect causing neurophysiological dysfunction . 
 administration of intravenous steroid would do at this stage , followed by constant infusion for following 2448  h , may help ameliorating the mass effect and improving the neurologic outcome . 
 alternatively , immediate pedicle screw changing policy showed absolute recovery of nerve injury.conclusioninsertion of pedicle screw in spinal surgery has a risk of complication that could be treated by pedicle screw changing policy . 
Introduction
Case presentation
Discussion
Somatosensory evoked potential
Transcranial electric muscle evoked potentials (tceMEP)
Spontaneous electromyography (freerun EMG)
Triggerd EMG
Steroid injection
Longer segment stabilization
Conclusion
Disclosure