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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6051_Библиотеки_им_академика_М_И_Перельмана
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Avoiddamagingthesupra- and intraspinousligamentsandligamentumflavum between thecranialfusedlevel
andtheadjacentsegment,aswellasbetweenthecraniallevelsoffusion.
Avoiddamagingthesupra-andinfra-adjacentfacetsandviolatingthecranialdiskspacewithpediclescrews.
References
FiveMust-ReadReferences
1.HalvorsonTL, Kelley LA, Thomas KA,WhitecloudTSIII,CookSD. Effectsof bone mineral density onpedicle
screwfixation.Spine1994;19:2415–2420PubMed
2.DeWaldCJ,StanleyT.Instrumentation-relatedcomplicationsofmultilevelfusionsforadultspinaldeformitypatients
over age65: surgicalconsiderations and treatment options inpatients with poor bone quality. Spine 2006;31(19,
Suppl):S144–S151PubMed
3. Butler TE Jr, Asher MA,JayaramanG, Nunley PD,RobinsonRG. The strengthandstiffnessof thoracic implant
anchorsinosteoporoticspines.Spine1994;19:1956–1962PubMed
4. Mummaneni PV, Haddock SM, Liebschner MA, Keaveny TM, Rosenberg WS. Biomechanical evaluation of a
double-threadedpediclescrewinelderlyvertebrae.JSpinalDisordTech2002;15:64–68PubMed
5. McKoy BE, An YH. An expandable anchor for fixation in osteoporotic bone. J Orthop Res 2001;19:545–547
PubMed
6. Frankel BM, D’Agostino S, WangC. A biomechanical cadaveric analysis of polymethylmethacrylate-augmented
pediclescrewfixation.JNeurosurgSpine2007;7:47–53PubMed
7. Chang MC, Liu CL, Chen TH. Polymethylmethacrylate augmentation of pedicle screw for osteoporotic spinal
surgery:anoveltechnique.Spine2008;33:E317–E324PubMed
8. Aydogan M, Ozturk C, Karatoprak O, Tezer M, Aksu N, Hamzaoglu A. The pedicle screw fixation with
vertebroplasty augmentation in the surgical treatment of the severe osteoporotic spines. J Spinal Disord Tech
2009;22:444–447PubMed
9.BurvalDJ,McLainRF,MilksR,InceogluS.Primarypediclescrewaugmentationinosteoporoticlumbarvertebrae:
biomechanicalanalysisofpediclefixationstrength.Spine2007;32:1077–1083PubMed
fixation in osteoporotic spines and comparison of its clinical results and biomechanical characteristics with the
needleinjectionmethod.JSpinalDisordTech2013;26:305–315PubMed
WinnHR,ed.Youmans’NeurologicalSurgery.Philadelphia:Elsevier;2011
augmentationoflumbarpediclescrewpulloutstrength.SpineJ2002;2:255–260PubMed
resistanceagainstpull-outforceintheosteoporoticcaninelumbarspinemodel:apilotstudy.SpineJ2005;5:239–
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lumbosacralspine.ClinOrthopRelatRes1986;203:99–112PubMed
morphologyandbiomechanicalstabilityintheimmatureporcinespine.Spine2006;31:E826–E829PubMed
densitytopull-outresistanceoftriangulatedpediclescrewconstruct.JSpinalDisord1997;10:12–19PubMed
trajectory technique of thoracic pedicle screw fixation: a biomechanical analysis. Spine 2003;28: 2058–2065
PubMed
comparisonofthetranspedicularandextrapediculartechniques.Spine2006;31:E355–E358PubMed
into the apexof the sacralpromontory over bicorticalfixation: a biomechanicalanalysis. Spine 2002;27:806–811
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biomechanicalanalysis.Spine2003;28:2066–2071PubMed
fusionconstruct.Spine2003;28:S234–S242PubMed
intactvertebrafromfatigueinjury:anexvivobiomechanicalstudy.Spine2009;34:356–364PubMed
OrthopRes2006;24:917–925PubMed
6
The Incidence and Management of Acute
NeurologicComplicationsFollowingComplex
AdultSpinalDeformitySurgery
JosephS.ButlerandLawrenceG.Lenke
Introduction
Significant advanceshavebeen made in adult spinaldeformity (ASD) surgery overthe
pastseveralyears. Improvementsin pediclescrewtechnology andthe increasinguseof
three-column osteotomies have made more powerful deformity corrections possible.
Nonetheless, loss of neurologic function after ASD surgery remains a serious and
potentially devastating complication, with profound consequences for health-related
quality of life. Intraoperative neurophysiology monitoring has become a reliable and
effectivemodalitytooptimizeneurologicsafetyduringASDsurgery.
1,2
Furthermore,the
increasinguseofimage-guidednavigationsystemshasledtosignificantimprovementsin
the accuracy of pedicle screw placement.
3,4
This chapter discusses the management of
acute neurologic complications in complex ASD surgery and proposes a treatment
algorithmtodealwiththesecomplicationsinsafeandeffectivemanner.
Prevalence
The incidence of neurologic complications in ASD patients undergoing deformity
correction surgery hasbeen difficulttodetermine. Multipleflaws exist inthe published
data,withalackofhigh-qualityprospectivestudies,significantdatavariability,andalack
of rigorous and validated measurements of neurologic function. Nonetheless, the
incidenceof neurologic deficitsfollowing ASDsurgery hasbeen previouslyreported as
rangingfrom0%toover10%.
5–9
Two previous studies, one from a single institution,analyzedprospectively collected
datatoidentifycomplications,butneitheroneusedavalidatedscoringsystemtoquantify
neurologicfunction.
10,11
All studiescouldmore accuratelybe describedas retrospective
studiesof prospectivelycollected data.But anaccuraterate ofneurologic complications
aftercomplexASDsurgeryiscriticalforinformeddecisionmakingforbothpatientsand
surgeons. Furthermore, it is crucial to be able to measure changes in neurologic
complicationratesinastandardizedfashionsoasto accuratelyevaluate newtechniques,
technologies,andtherapiesinASDsurgery.
The Scoli-Risk-1 trial is a recent prospective, multicenter observational study
attemptingtoaccuratelyassesstheneurologiccomplicationratefollowingcomplexASD
surgeryusingtheAmericanSpinalInjuryAssociation(ASIA)scoringsystem(Fig.6.1).
12
Atotalof276patientswereenrolledfrom15internationalcenters.Athospitaldischarge,
23.1%ofpatientshadameasurablelowerextremitymotordeficit(i.e.,lessthan5/5motor
strength inall five major legmuscles) decreasing to 17.8%at 6 weeks and10.7% at 6
months postoperative. This study gives a clearer indication of the expected neurologic
complicationrate inASDpatients, potentiallysetting astandardfor futureclinicaltrials
aimedatloweringtherateofpostoperativeneurologicdeficits.
Fig.6.1TheAmericanSpinalInjuryAssociation(ASIA)scoringsystem.
MechanismsofNeurologicComplications
There are several proposed causes of intraoperative neurologic deficits during ASD
surgery.Intraoperative spinalcord, cauda equina,or nerveroot deficits mayresult from
directneurologictraumaduringinstrumentationsuchastheplacementofpediclescrews,
hooks,orsublaminarwires.Furthermore,intraoperativecorrectivemaneuversmayleadto
neurologic deficit secondary to either distraction of the neural elements or excessive
tensionon local vasculature,leading todecreased bloodflow andcord ischemia.Spinal
cord ischemia may also result from prolonged extreme hypotension (mean arterial
pressure [MAP] < 55 mm Hg), hypoxia secondary to decreased hemoglobin level, or
vascularcompromiseafterligationofthesegmentalvesselsinananteriorprocedure.
13
PatientEvaluationandPreoperativePlanning
Neurologiccomplicationsaremoststronglyassociatedwithprolongedcomplexsurgery,a
large amount of blood loss, combined anterior/posterior procedures, multistage surgery,
congenitalkyphosis orscoliosis,largeor rigidspinalcurves (Cobbangle> 90degrees),
preexisting myelopathy or neurologic deficit, and intramedullary spinal cord tumors.
Further risk factors include tethered cord, Arnold-Chiari malformation, syringomyelia,
andsplitcordmalformations.
A complete patient history and thorough physical examination still remain essential
elementstoanadequatepreoperativeworkup.Patientsshouldbeassessedforahistoryof
congenital deformities such as kyphosis and scoliosis, neurofibromatosis, and skeletal
dysplasia, which would infer a considerably increased risk of iatrogenic neurologic
complications.Thephysical examinationshould include athree-dimensional assessment
of the spine to evaluate patient posture, neurologic status, hip flexion contractures, leg
length inequality, pelvic obliquity, body habitus, and nutritional status. Meticulous
examinationofthemotor,sensory,andreflexfunctionaswellasgaitassessmentiscritical
in screening patients for potential intraspinal and brainstem anomalies such as tethered
cord,Arnold-Chiarimalformation,syringomyelia,andsplitcordmalformations.
Adequateradiologicalimagingiscrucialforoptimalsurgicalandneurologicoutcome.
However, it is technique-dependent, requiring visualization of the entire spine in the
coronalandsagittalplanes,includingthehipjoints,withallimagingtakenwiththepatient
standing with the knees fully extended for accurate measurement of sagittal balance
(sagittal vertical axis [SVA]), thoracic kyphosis, lumbar lordosis, and spinopelvic
parametersincludingpelvicincidence(PI),sacralslope(SS),andpelvictilt(PT).Lateral
dynamic standing lumbar X-rays may identify focal instability or spondylolisthesis.
BendingfilmsandsupineX-rayswithouttheeffectsofgravityhelpassesstheflexibility
ofadeformity.Oncetheappropriateradiographicstudieshavebeenobtained,thesagittal
andcoronalbalancecanthenbeassessed.
Magneticresonanceimaging(MRI)isusedasaroutinepreoperativeradiographicstudy
to assess central canal stenosis, facet hypertrophy, pedicular anomaly, foraminal
encroachment, and degenerative disk disease. It also helps determine the presence of
intraspinal anomalies. Patients with suspected low bone mass or with established
osteoporosisshouldhaveadual-energyX-rayabsorptiometry(DEXA)scanperformedto
optimizesurgicalplanning.
IntraoperativePreparation
Meticulousintraoperativepreparationisrequiredforthesafeandeffectivemanagementof
intraoperative complications. Before induction of anesthesia, the surgical team should
discuss with the anesthesia and neuromonitoring teams and operating room staff the
patient’s medical situation,the intended procedure, andsurgical time frame.An arterial
line may be used to monitor MAP. Somatosensory evoked potential (SSEP) and motor
evokedpotential (MEP)leadsare placedand checkedbeforethe patientis turnedtothe
prone position. The upper extremities are padded and positioned to avoid stretch or
compressionofthebrachialplexus,andcareistakentoensurethatthepressureareasare
wellpadded.Forced-airwarmingblanketspreventhypothermia,particularlyinprocedures
oflongduration.
Maintaining adequate blood pressure is essential. However, a balance should be
maintainedtominimizeintraoperativebloodlossandtransfusions,yetensuringadequate
spinalcordperfusion.AMAPof<55mmHghasbeenassociatedwithanincreasedrisk
ofspinalcordischemia.
14
However,mildhypotensiveanesthesiaisoftenusedtominimize
bloodloss,particularlyduringthesurgicalapproach,withtheMAPmaintainedat65to70
mm Hg. Approximately 30 minutes before performing corrective maneuvers, the
anesthesia team should gradually elevate the MAP to > 70–80 mm Hg to maintain
adequatecordperfusionduringspinalcolumnmanipulationanddeformitycorrection.
IntraoperativeNeuromonitoring
StagnaraWake-UpTest
The Stagnara wake-up test has been widely used in the intraoperative assessment of
neurologic function. It assesses primary motor cortex, anterior motor pathways of the
spinal cord, nerve roots, and peripheral nerves. However, it gives only a gross
approximation of the function of these elements and does not directly measure any
components of the sensory system.
15
This test involves a temporary reduction in
anesthesia,afterwhichthepatientisaskedtomovetheupperandlowerextremities.The
testislimited,asitisentirelyreliantonpatientcomplianceandcannotbeusedinpatients
unable tofollow commands becauseof intellectual and developmentaldisability,young
age,orpreoperativeweakness.Thetestitselfcarriesrisk,includingself-extubation,lossof
intravenous access or of safe patient-positioning on the table, air embolism, and
postoperativerecollectionoftheevent.
The wake-up test was historically the benchmark for intraoperative neurologic
assessment, and is still used at some centers in conjunction with advanced
neuromonitoring techniques as a means of confirming neurologic status. Properly
administered, the wake-up test should be 100% accurate in detecting gross motor
changes.
15
Althoughthelimitationsofthetestpreventassessmentoffinemotorchanges,
it will alert the surgeon to the most clinically significant neurologic deficits. It is used
whenthereisanyproblemobtainingspinalcordmonitoring(SCM)signals(suchasin a
patient with thoracic myelopathy) and also in patient’s who have had SCM changes
meetingevokedpotentialwarningcriteriawhentheresponsescannotbeimproved.Italso
should always be performed at the end of the surgical procedure prior to the patient’s
leavingtheoperatingroom.
SomatosensoryEvokedPotentials
Somatosensory evoked potentials assess the posterior columns of the spinal cord, in
addition to the cerebral cortex and mixed peripheral nerves. The posterior columns are
responsible for proprioception as opposed to pain and temperature. Although
proprioceptivelossisnotasdebilitatingasamotordeficit,itcanhaveasignificantimpact
onactivitiesofdailyliving.AsSSEPsaresensitive tofocal posteriorcolumn andglobal
spinalcordissues,theyactasagoodsurrogateforotherneuralpathways.However,there
aresituationswhen amotordeficit mightnotbe demonstratedonSSEPmonitoring.For
example, anterior vascular territorycompromise without concomitant posterior vascular
changesmightnotbeaddressedbySSEPmonitoring.
Somatosensoryevokedpotentialscontinuetobethemostfrequentlyusedintraoperative
monitoringmethodtoassesstheintegrityofthedorsalcolumnbutcannotbereliedonto
monitor motor function directly. Reports of postoperative paraparesis in the absence of
intraoperative SSEP signal change underscores this important limitation.
16
SSEP
dependability falls off when applied to patients with preexisting neurologic conditions.
IndividualnerverootinjuryisnoteffectivelymonitoredbySSEPs.Missednerverootor
isolatedmotorpathwaycomplicationsarenotfailuresofthemodalitybutratherareissues
outside of SSEP monitoring capability, highlighting the need for alternative or adjunct
monitoringapproaches.WarningcriteriaforSSEPsatoutinstitutionincludegreaterthana
60%decrease inamplitudeor a10% increaseinlatency ofthe signalascompared with
baselinevalues.
MotorEvokedPotentials
Motorevokedpotentialsmonitorcorticospinaltractactivityviastimulationatthelevelof
the motor cortexor spinal cord and are selectivefor motor pathways. MEPmonitoring
relies on intervening thalamic synapses to prevent antidromic firing of spinal sensory
tracts.ThestimulationsitefortranscranialMEP(tcMEP)isthecerebralcortex.MEPend-
point data are ascertained from the spinal cord (D-wave) or from the end muscle
compoundmotoractionpotential(CMAP).Stimuliarepresentedassinglehighvoltageor
multiple small stimuli. Sources of stimulation include magnetic and electrical. For
magnetictcMEP,acoiloverthecortexprovidesthestimulation.Electricalstimulusofthe
motorcortexisprovidedbysubdermalelectrodes.Althoughoccasionallyassociatedwith
scalpedemaandunreliablerecordings,corkscrewelectrodesarepreferablegiventheirlow
impedance and secure positioning in the scalp. Peripheral data are commonly
electromyographicviaCMAP.TheCMAPisbestmonitoredatsitesrichin corticospinal
tract innervationsuchas the distal limb muscles.Common recording sites are abductor
pollicisbrevisoradductorhallucisbreviswithviablealternativesoflongforearmflexors
andextensorsintheupperextremityandtibialisanteriorinthelowerextremity.Although
there does not appear to be any monitoring advantage to increasing the number of
monitoredmuscles,increasedmusclegrouptestingmightprovideabenefitinidentifying
positioning-relatedinjury.
Electromyography
The clinical applications of electromyography (EMG) and its specificity for the motor
systemledtotheintroductionofspontaneousEMG(sEMG)recordings.sEMGmyotomes
are preselected to coordinate with operative levels, and muscle relaxants must not be
utilized due to dampened or even absent activity. Continuous electrical activity to a
myotomeisrecordedandobservedandmaybeindicativeofrootirritation.Whenanerve
rootisnotedtobeexcessivelymanipulatedorimpinged,triggeringaburstofactivity,with
moreseverenervemanipulationandstretchofanerveroottrainactivityisalsonoted.One
wouldgenerallynotesilenceifthenerverootiscleanlysevered.Distalrecordingsitesare
typically pairedwith an intramuscularneedle or wireelectrodes inserted afterinduction
butbeforesurgery.
Triggered EMG (tEMG) has also been used as it is postulated that a high stimulus
intensitytEMGwilldemonstrateanintactcortexofapedicleholethroughwhichascrew
ispassed. Inapplication, bonehas highimpedancerequiring highthreshold tostimulate
theadjacentnerve.WhentEMGrequireshighstimulation,itdemonstratestheintegrityof
thepediclecortexandlackofperforation.Directstimulationofamisplacedpediclehole
withabreach,canactivatetheadjacentnerverootandevokeaCMAPintheappropriate
myotomes at lower stimulus intensities than would be expected with an imperforate
pedicle cortex.Clinical correlation isof course required,buttEMG attempts toprovide
dataonapathwayfrompediclescrewortracttothedistalsiteandcanbeusedinthoracic
spineoperationsifthe rectusabdominisorintercostalsmusculatureare monitoredasthe
distalrecordingsite.
MultimodalityIntraoperativeMonitoring
Somatosensory evoked potentials are the most common neuromonitoring modality
employed,butarenotalwaysasufficientproxyforallcordfunction.Failingtorecognize
thelimitationsofSSEPscanleadtodevastatingconsequences.Itmustbeemphasizedthat
no single modality sufficiently monitors all spinal cord pathways. If the goal of
intraoperativeneuromonitoringistodetecttheonsetofdeficitsforbothsensoryandmotor
pathways, then no single modality meets the goal; however, a combination of testing
methods might. Multimodality intraoperative monitoring uses all electrophysiological
techniquesandcanprovideintraoperativeinformationabouttheneuralstructuresatrisk.It
permitsassessmentofbothascendinganddescendingpathwaysconcurrently,providinga
certain degree of redundancy because many types of intraoperative injuries will
compromisebothmotorandsensorypathways.
IntraoperativeNeurologicComplications
Significant ASD surgery requires continuous neuromonitoring, especially during
placementofinstrumentationanddeformitycorrection.Immediateactionisrequiredwhen
damage to the spinal cord or a peripheral nerve is suspected at any time during the
procedure in response to changes of > 50% amplitude and > 10% latency in the
SSEP/MEP signals. An algorithm may aid the primary surgeon in determining the
causative factor and initiating appropriate treatment. Reassessment of neuromonitoring
signalstrengthisperformedaftereachstep.Thespecifictimingofeachofthestepslisted
belowisnotuniversal;rather,timingshouldbedeterminedonacase-by-casebasis.Each
subsequentstepisinitiated ifthepatientfailstodemonstrate improvementinneurologic
functionaftertheprevioussequentialcorrectivemaneuvershavebeenperformed.Hereis
ageneralchecklistoffactorstoconsiderwhenSCMchangesoccur:
Ten-ItemChecklistinResponsetoLosingSCMDataorMeeting
WarningCriteria(SSEPsorNeurogenicMEPs)
1.CheckwithpersonneltomakecertainSCMdataissueisreal(experiencematters).
2.Beawarethatanincreaseinbloodpressure(MAP≥80–90mmHg/systolicbloodpressure>120mmHg)may
require a quick dose of epinephrine/norepinephrine or a dopamine drip; provide blood products if needed
(hemoglobin>9).
3.Releaseanytractiononpatient’sspinalcolumn(halo,halo-femoral,etc.).
4.Palpatethedura,checkingforimpingement(ifspinalcanalisopen),suchaspriorosteotomies/laminectomies.
5.Reverseanycorrectivemaneuver;alsoconsidershorteningofspinalcolumn.
6.Confirmtheabsenceofspinalsubluxation.Considerusingtemporarybilateralrodsduringclosure.
7.Considerimplantmalposition(screw/hook/wire)iftemporallyrelated,whichmightindicateduralimpingement.
8.Orderawake-uptestifthemonitoringdatahavenotimprovedorreachedbaseline.Also,thisisagoodtimeto
takeadeepbreathandreflectonpossibleadditionalissues.
9.ConfirmthatelevatedMAPisbeingmaintained.
10.Considerapicalspinalcorddecompressiontorelievetightneuraltissue.
IncreaseSpinalCordPerfusion
Immediately following identification of neuromonitoring signal changes, the
hemodynamic and oxygenation status of the patient should be optimized to improve
perfusion to the spinal cord. The MAP is elevated to > 80 mm Hg or 20% above
baseline.
17
Hemoglobinandbloodglucoselevelsareevaluatedandcorrectedifrequired.
Bodytemperatureshouldbemaintainedat> 36.5°Ctooptimizeneuromonitoring.These
measureshavebeenshowntoincreasespinalcordperfusion.
18
StagnaraWake-UpTest
Changes in neuromonitoring signal suggestive of persistent neurologic deficit may be
cause for considering a confirmatory test. Prior to the induction of anesthesia, patients
shouldbecounseledthattheywillbeaskedtoperformseveralcommandsuponawaking
from anesthesia. Frequent assessment of the patient’s neuromonitoring status is
recommended as instrumentation is placed and corrective maneuvers performed. This
enables the surgeon to most reliably pinpoint the possible inciting factor, such as a
malpositioned implant or tension on the cord caused by corrective maneuvers. Thus,
potentially problematic instrumentation can be removed or correction relaxed while
waitingforthepatienttoawakenfromanesthesiaforthewake-uptest.However,onemust
also understand that atime lag can occur between the application of acorrective force
(e.g.,distraction)andthediminution/lossofSCMsignals.Thus,prudentresponsestoany
SCM change that meets the warning criteria must be made based on the many factors
involved,includingtheMAP,anyrecentcorrectionmaneuvers,andthetypeofdata.
ReleaseofCorrection
Thesurgeonshouldconsiderreleasingthetensiononthespinewhenallparameters(e.g.,
MAP,temperature,hemoglobinlevel)havebeenreasonablyaddressedandthereisstillan
absenceof expectedmotorfunction withthewake-up test.Afterrelease ofcorrection,a
second wake-up test can be considered when SSEP/MEP signals indicate persistent
abnormality.If animprovementin thewake-up testorin neuromonitoringis discovered
afterthe releaseof surgicalcorrection,the surgeonhasthe optionof fusingthe spinein
situorattemptingamoremodestcorrection.Whennoimprovementinneurologicfunction
is elicited after the release of tension, all screws and hooks should be reassessed. The
stabilityof the spinealso shouldbe evaluated.When removalof instrumentationwould
compromisethestabilityofthespinalcolumn,suchasaftervertebralbodyresection,the
surgeonmaybeforcedtomaintain theexistinginstrumentationandfusethespine under
the least amount of tension. If osteotomies have been performed, the canal should be
examined for fragmentsofbone, Gelfoam, or bone wax, which may becontributingto
cordcompression.
Pediclescrew positionshould becritically examinedin lightof amonitoring change.
The position of each screw can be reassessed using one measure or a combination of
several. High stimulation thresholds of each fixation point, as indicated by triggered
electromyography, theoretically indicate intracortical screw position secondary to
increased resistance to current flow through cortical bone. Any pedicle screw with a
markedlylowerelectromyographythreshold(<60%)inrelationtotherestoftheconstruct
shouldbereassessed,asthismayindicateapossiblepediclewallbreach.
19
Screwposition
canalsobeevaluatedwiththeuseofintraoperativefluoroscopy.Apediclescrewtippast
themidlineofthevertebral bodynotedonposteroanteriorradiographsissuggestiveofa
medial pedicle breach. In the presence of any or all of these signs, the screw may be
removed to reassess the tract with direct palpation. A small laminotomy may also be
performed to evaluate the integrity of the medial pedicle cortex with or without screw
removal. Early removal of instrumentation may increase the possibility of neurologic
improvement, provided the spine will not be significantly destabilized with removal of
instrumentation.
Theabilitytoobtainadequatepostoperativeimagingstudiesisonepotentialadvantage
ofremovalofinstrumentation.Thequalityofcomputedtomography(CT)andMRIscans
issuperiorwhennoinstrumentationispresenttocreateartifact.Eventitaniumconstructs
canproduceartifacton CTor MRIscans.AnMRIscanmay bedoneinthepresenceof
titaniuminstrumentation; otherwise,a CTscan canbe ordered. Ifthe instrumentationis
retained and standard CT or MRI scanning is inconclusive, a CT myelogram can be
performed. If an abnormality (e.g., screw malposition, hematoma) is identified, urgent
returntotheoperatingroomisindicatedfordecompressionorremovalofinstrumentation.
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