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LumbarLordosis
In additionto differentcurvepresentations in thecoronal plane, sagittalalignment may
alsobedifferentbetweendenovoandidiopathicscoliosis, especiallyintheearlystages.
Lumbar lordosismay remainnormalin idiopathicscoliosis because diskheight may be
maintained for along time. In de novo scoliosis,however, lumbarlordosismay not be
preserved because of early disk collapse. Bao et al
11
also demonstrated that de novo
scoliosis patients with severe disk degeneration have lumbar hypolordosis or kyphosis
(Fig. 7.2). Moreover, osteoporotic fracture is more frequently observed in de novo
scoliosis,particularlyinfemalepatients,greatlycontributingtolumbarkyphosis,whereas
in idiopathic scoliosis, the degenerative pathologies are not the primary cause, and
osteoporoticfracturemaybelesscommon.
ContributionofDiskDegenerationtoSpinalImbalance
andCurveSeverity
Spine imbalance in the sagittal orcoronalplane has an important impact on the health
status and treatment options in patients with de novo scoliosis. Sagittal imbalance is
closely correlated with poorhealth-relatedquality of life (HRQOL). Importantly, it has
been well documented that coronal imbalance is also one of the main causes of
unsatisfactory appearance, impaired function, and back pain.
12
Because the established
consensusintermsoftheoriginofdenovoscoliosisisthatitistriggeredbyasymmetrical
disk degeneration, our team conducted a study specifically focused on the correlation
betweendiskdegenerationandspinalimbalance.
11
We quantified disk degeneration using the Pfirrmann classification, which describes
fivegradesofdiskdegenerationonmagneticresonanceimaging.
13
Eachgradeofdiskwas
scoredwithaspecificnumbertoenabledoingcalculations;forexample,gradeIwasgiven
a score of5, whereas grade V wasgiven a score of 1. Thus,higher scores represented
healthierdiskconditions.
Theresultsofourstudyrevealedthatdiskdegenerationatthelowerendvertebra(EV)
wasstronglycorrelatedwithsagittalimbalance(Fig.7.2).Wefoundthatthegradeofthe
lowerEVdiskreachedameandegenerationscoreof2.32,beingthesecondmostseverely
degenerated disk after the apical disk. There may be three stages of disk degeneration,
correlated with stability and motion: dysfunction, instability, and stabilization. With
moderate disk degeneration, the disk might become unstable. Also, there might be a
tendency for instabilityto lie in moderately degenerated diskswithwell-preserved disk
height,whereasmobilitymaydecreaseandrestabilizeinthecollapseddisks.Thisfinding
supportedourassumption thatlowerEVdiskdegenerationwasmoreresponsibleforthe
sagittal imbalance because its stability was jeopardized. However, we failed to find
significant correlation between coronal imbalance and disk degeneration. Certainly,
degeneration of the posterior elements, including the facet joints and the paraspinal
muscle, is another accepted factor accounting for de novo scoliosis; therefore, it is
assumed that unstable posterior elements instead of disk degeneration may be the
importantcauseofcoronalimbalanceinlumbardegenerativescoliosis.Thedegenerative
facetjointswithosteoarthritismaybetheprimarycause,ormaybesecondarytotheloss
of disk height, leading to vertebral instability and increased segmental axial mobility,
whichmaycontributetocoronalimbalance.Asymmetricatrophyofparaspinalmusclesis
another possible factor influencing coronal balance. The degree of instability varies in
each individual, based on the slip in the sagittal plane, translational dislocations in the
coronalplane,andthree-dimensionalrotationalsubluxation.
CorrelationbetweentheCobbangleandapicaldiskdegenerationwasalsonoted.The
more degenerationthe apical diskpresented, the largeris the Cobbangle. Such a close
relationshipbetweendegenerationoftheapicaldiskandtheCobbanglecanbeexplained
bythepathologyofdegenerativescoliosis:asymmetricdegenerationintheapicaldiskwill
leadtoasymmetricdiskcollapse,inducingthespinetobendtheapicalfacetjoints,which
inturnexacerbates thedegenerationofthe concaveside.Inaddition, wealsofoundthat
regional lumbar disk degeneration grade is correlated with sagittal malalignment,
including an anteverted C7PL and lumbar kyphosis (Fig. 7.2). Decreases in lumbar
lordosis in patients with disk degeneration, as evidenced in our study, explain why de
novo scoliosis patients with severely degenerated disks had lumbar hypolordosis or
kyphosis.
CoronalBalanceofAdultDeformity
CoronalBalanceAssessment
The concept of balance of the spine has been extensively described by the Scoliosis
ResearchSociety(SRS).Theconceptimpliesthat,inboththecoronalandsagittalplanes,
theheadispositionedcorrectlyoverthesacrumandpelvis,inbothatranslationalandan
angular sense. Fromthefrontal view of the trunk, balance implieshorizontal shoulders
andthe trunkevenlydistributed aboutthe verticallinepassing throughthe centersacral
vertical line (CSVL). Spinal balance in the coronal plane can be determined as the
displacement of the most cephalad vertebra from the CSVL in both a distance (frontal
planeoffset)andanangle(offsetangle).Inpractice,thedefinedcephaladvertebrausually
is C7 or T1(Fig. 7.3). Compensation in the coronal plane is usually referredtoas the
translationof themidpointof C7in relationtoCSVL(measured inthesamemanneras
coronal balance [CB]). It primarily describes the position of the head over the pelvis.
Decompensation occurs when this alignment strays from the midline by more than a
thresholdvaluespecifiedbytheinvestigators,usuallyreportedas2cm.
The wordbalance implies a static alignment in the standing(or unsupported seated)
position, whereas compensation and decompensation refer to the result of dynamic
alignment. In detail, compensation signifies the active process of becoming balanced,
whereas decompensation indicates a failure to achieve balance, especially after an
interventionsuchassurgery.
RelationshipBetweenCoronalBalanceandQualityofLife
Inpatientswithadultscoliosis,theimpactofsagittalbalanceonclinicalhealthstatushas
beenextensivelydiscussed,whereastheimpactofcoronalbalanceonfunctionaloutcomes
is less clear. In contrast topatientswith idiopathic scoliosis, patients with degenerative
lumbarscoliosishaveanincreasedlikelihoodofimbalanceinthecoronalplane.Because
ofasymmetricaldegenerativechangesandvertebralwedgingintheapicalregion,coronal
imbalanceisfrequentlyobserved.AccordingtothestudybyDaubsetal,
14
13of85(15%)
adult scoliosis patients with preoperative coronal imbalance had worsening coronal
balance of more than 1 cm after surgery. This finding suggests that the incidence of
postoperativeimbalanceinthecoronalplaneisunderestimated.
Fig.7.3a–cExamplesoftheclassificationofthecoronalbalancepatterninadultscoliosis.(a)TypeAina64-year-old
woman without obvious truncal asymmetry. (b) Type B in a 63-year-old woman with the trunk shifting toward the
concaveside.(c)TypeCina61-year-oldwomanwiththetrunkshiftingtowardtheconvexside.
It has been found that coronal imbalance correlates with significant clinical
manifestations suchaspelvic obliquity, sitting or standingimbalance, as well as severe
cosmetic truncaldeformity.Moreover,coronal imbalance isone of themain underlying
causesoftheprogressionofdeformity,backpain,andfunctionalcompromise.Axialpain
usually derives from the convexity of the curve, and leads to further deterioration of
coronalimbalance.Radicularpainandneurogenicclaudicationmainlyoriginatefromthe
compressionontheconcavityofthecurve,orfromdynamicoverstretchingontheconvex
side.
1
Deterioration of these symptoms runs in parallel with the increase in coronal
imbalance to some extent. To address these problems, it is important to correct the
preoperativecoronalimbalance.
To help elucidate the factors that are most crucial for improved outcomes, several
studieshaveattemptedtocorrelateradiographicfindingswithclinicalsymptomsinadult
scoliosis.Glassmanetal
15
reportedthatsignificantcoronalimbalancewasassociatedwith
painanddysfunctioninunoperatedpatients, andcoronalimbalancewasnotascritical a
parameter as sagittal imbalance in prediction of symptoms. However, Daubs et al
14
showedthatsagittalbalanceisthestrongestpredictorofimprovedfunctionaloutcomesin
adult scoliosis patients. They found that restoring sagittal balance in patients with
combinedcoronalandsagittalimbalanceseemstobethekeytoimprovingthefunctional
outcomes. In terms of patients with coronal imbalance alone, improvement in coronal
balancewasasignificantpredictorofimprovedsurgicaloutcomes.
14
Insomestudies,coronalimbalancehasalsobeenreportedtoleadtodecreasedHRQOL
and increased risk of implant failure in adult scoliosis patients.
15–17
In the study by
Glassmanetal,
15
significantcoronalimbalanceofgreaterthan4cmwasassociatedwith
morepainanddysfunctionforunoperatedpatientsbutnotforoperatedpatients.Ploumis
etal
16
reportedthatpatientswithcoronalimbalanceofgreaterthan50mmshowedworse
physicalfunctionscores.Choetal
17
demonstratedthatpreoperativecoronalimbalanceled
to more implant failures, requiring removal of the implant. Therefore, improved
postoperativecoronalbalanceshouldbethegoalinordertoimprovetheHRQOLaswell
astoreducetheneedforrevisionsurgery.Atourcenter,postoperativecoronalimbalance
wasoneofthefactorsthatcontributedtoimplantfailure.
DecompensationintheCoronalPlane
Asmentionedabove,decompensationinthecoronalplaneimpliesdynamicmalalignment
of the spine, commonly measured as CB (translation of the center of C7 in relation to
CSVL) beyond a specified threshold value. In adolescent idiopathic scoliosis patients,
decompensationwasusuallydefinedascoronalimbalanceofmorethan2cm(measured
in the same manner as CB). In adult scoliosis patients, the threshold value of
decompensationinthecoronalplanevariedamongstudies.Glassmanetal
15
reportedthe
associationbetween coronalimbalanceof greaterthan4 cmanddeterioration inclinical
symptoms in nonoperated patients. Daubs et al
14
and Ploumis et al
16
defined coronal
imbalanceas C7PL> 4cmand >5cm lateraltoCSVL, respectively.Inarecentstudy,
withemphasis oncoronal imbalancein adultspinaldeformity patientstreated withlong
fusions,Ploumisetal
18
alsoemployedacriterionof4cm.
In a study by the SRS that classified adult scoliosis according to the King/Moe and
Lenkeclassifications, coronalimbalancewas consideredtobe oneofthe globalbalance
modifiers.
19
ImbalancewasconsideredtobepresentiftheC7PLwaslocated>3cmtothe
right or left of the CSVL. We recently surveyed a consecutive series of degenerative
lumbarscoliosispatients toevaluatecoronal balance,withthebalancethresholdsetat 3
cm. We found a high prevalence of preoperative coronal imbalance in adults with
degenerativelumbarscoliosis.Inthesepatients,imbalanceoccurredeitherontheconcave
side, namelyC7 deviating towardthe concave sideof the maincurve with referenceto
CSVL(Fig.7.3b),orontheconvexside,withC7deviatingtowardtheconvexside(Fig.
7.3c).
PostoperativeCoronalDecompensation
Postoperative coronaldecompensation is amajor complication inadult scoliosis.
14,18
In
addition to the Daubsetal
14
finding reported above (see section RelationshipBetween
Coronal Balance and Quality of Life), Ploumisetal,
18
in a cohort of 54 adult patients
treatedwith longfusions, foundpostoperative coronaldecompensationinsevenpatients
withpreoperativecoronalimbalanceandinfourwithout,atsixweekspostoperatively.At
aminimum2-yearfollow-up,fourmorepatientswithoutinitialimbalancewereobserved
with coronal decompensation. The authors reported that postoperative coronal
decompensation was found in an increased number of adult spine deformity patients.
18
But so far, the underlying factors that predict postoperative coronal decompensation
remainunclear.
In theory, decreased compensation of the segments above and below the fusion pre-
disposes the patient to postoperative coronal decompensation. Multiple deformity- and
surgery-related factors are probably associated with the occurrence of postoperative
coronaldecompensation.
Deformity-RelatedFactors
Wefound thatthepreoperative coronalimbalance patternplays animportantrole inthe
occurrence of postoperative coronal decompensation. A curve with imbalance to the
convexsidepredisposestofurther decompensation,particularlywhenosteotomiesofthe
posterior elements,such asSmith-Petersen osteotomy (SPO),or through threecolumns,
suchaspediclesubtractionosteotomy(PSO),areundertaken.
6,20
Forcaseswithimbalance
to the convex side, compression maneuvers on the convex side at the level(s) of the
osteotomy, which are performed to close the osteotomy gap, may lead to further
inclination of the trunk toward the convex side. As in congenital thoracolumbar
kyphoscoliosis, wealso noticed that patientswith preoperative conveximbalancehad a
higherrateofpostoperativecoronaldecompensationafterthree-columnosteotomies.
Atthesame time,decreased compensation aboveand belowtheinstrumentation also
play an important role in the development of postoperative coronal decompensation,
becausethecompensationpotentialoftheunfusedsegmentscomesmainlyfromthedisks
and paravertebral musculature. Hence, the more degenerative changes the adjacent
vertebraecephaladorcaudaltothefusionlevelsmanifest,theworsethepotentialability
for these unfused segments to compensate, resulting in an increasing likelihood of
postoperativecoronaldecompensation.
Surgery-RelatedFactors
Among the surgery-related factors that have impact on the occurrence of postoperative
coronal decompensation, the lower instrumented vertebra (LIV) selection is of upmost
importance.EndingLIVatavertebrathatcannotbecomehorizontalduringsurgerycarries
thepotentialriskofpostoperativedecompensation.IfthereisaresidualobliquityofLIV
inthecoronalplane,aninclinationofthetrunkisboundtooccur,becausethediskbelow
LIVprovideslimitedrangeofmotion.Asmentionedpreviously,wefoundthatthedisks
of thelower lumbar region showed significantdegenerative changes. The physiological
function of these disks is correspondingly compromised. Apparently, fusion distally
stoppingatavertebrathatcannotbecomehorizontalplacesthecoronalbalancepatternat
riskofdecompensationaftersurgery.
In addition, proper determination of the upper instrumented vertebra (UIV) can
diminish the incidence of coronal decompensation. A location of UIV below the end
vertebra of the main curve can result in inclination of the fusion with reference to the
CSVL.Iffusionextendsintothethoracicregion,however,amuchmorecephaladlocation
oftheUIVthantheendvertebraalsocarriestheriskofdecompensation,becauseitlowers
the number of thoracic vertebrae with compensation potential. Moreover, inclination of
UIVtotheconvexsideofthemaincurveprobablyimpedesbalanceinthecoronalplane
throughtheadverseimpactontheauto-compensationmechanism.
An inappropriate osteotomy algorithm may contribute to postoperative coronal
decompensationaswell.Three-columnosteotomiesusuallybeginattheapexandfromthe
convex side.
20
This is effective in the correction of cases with preoperative coronal
imbalancetotheconcaveside.Foracasewithpreexistentimbalancetotheconvexside,
however, such a maneuver might aggravate the imbalance because of the compression
forcesattheosteotomizedsitefromtheconvexside.
In practice, surgeons perform sagittal balance restoration more than in the coronal
plane, and the balance pattern and the compensation potential in the coronal plane are
sometimes ignored. Such an attitude toward coronal plane balance is evidently an
underlying risk factor for postoperative coronal decompensation. Multiple studies have
demonstrated that coronal imbalance accompanied by sagittal imbalance is a more
commonclinicalscenario.
14,16,19
Therefore,adequateattention needstobepaidnotonly
to the sagittal plane but also to the coronal plane. In patients complaining of sagittal
imbalance, Bridwell
20
classified the coexistent coronal imbalance with into type Aand
typeB.Intype A,thepatient’sshouldersand pelvisaretiltedinoppositedirections;the
shoulderiselevatedatthesidewherethepelvisislower.Conversely,withtypeB,boththe
shouldersandthepelvistiltinthesamedirection.AnasymmetricalPSOisoftenusefulin
correcting type A biplanardeformities.
21
The moreradical techniques such as vertebral
columnresection(VCR)aresometimesusefulfortheraretypeBdeformities.
20
PreventionofPostoperativeCoronalDecompensation
ANovelClassificationofCoronalBalancePattern
A discrepancy exists between sagittal imbalance, which is well accounted for in the
traditionaltreatmentalgorithm,andimbalancein thecoronalplane, whichthealgorithm
ignores.Furthermore,postoperativecoronaldecompensationisanimportantcomplication
thataffectssurgicaloutcomeandincreasestherevisionrate.Toaddressthisproblem,we
have established a novel classification regarding coronal balance patterns for adult
scoliosis.
ThisclassificationisbasedonCB,whichismeasuredasthedistanceofthemidpointof
C7 relative to the CSVL on standing posteroanterior X-ray films (Fig. 7.3). Vertebral
alignment in the coronal planeis considered to be balanced if CB is less than 3 cmat
eitherside;otherwise,itisconsideredtobeimbalanced.Patientswithabalancedcoronal
patternarecategorizedastypeA(Fig.7.3a).Patientswithanimbalancedcoronalpattern
(CBmorethan3cm)arecategorizedastypeBiftheimbalanceisontheconcavesideof
themaincurve(Fig.7.3b)andtypeCiftheimbalanceisontheconvexsideofthemain
curve(Fig.7.3c).
OsteotomyOptionsBasedonThisClassification
ForacoronalpatternoftypeAortypeB,thethree-columnosteotomy,ifnecessary,should
beperformedrightattheapexfromtheconvexside,soastorestorelumbarlordosisand
to reestablish coronal balance when the compression forces are applied to close the
osteotomygap.ThisosteotomyoptionisveryeffectiveincorrectingpatientswithatypeB
coronalpattern.ButintypeCpatientswithpreoperativecoronalimbalanceontheconvex
side, thisosteotomy optionmight be inappropriatedue to thecompression forcesatthe
apex. Although it is rare, intraoperative dislocation after three-column osteotomy can
occur as a severe complication, due to compulsively rectifying the imbalanced trunk,
whichisaccompaniedbyarelativelyrigidlumbosacralhemicurve.
Torestoreabalancedspinewiththetrunkcentrallyoverthepelvis,anovelosteotomy
strategy has been suggested for cases with type C (Fig. 7.4). First, a three-column
osteotomyneedstobeperformedatamoredistallevel,usuallyattheL4vertebraorthe
L4/5diskfromtheconcavesideofthemaincurvetorestorethebalanceofthetrunkover
the pelvis. Second, the apical region is then corrected. In cases with kyphosis, an
additional three-column osteotomy can be done at the apex. The optimal strategy of
osteotomyfortypeCbeginsfromtheconcaveside,andconvertsthepreviousimbalance
patternintoatypeApattern.
Inaddition,anasymmetricalPSOmightbeanalternateoptionforpatientswithatype
Cpattern.Toyoneetal
21
described thetechniqueofasymmetricalPSOthroughwhich a
coronalcorrectionwaswellachieveduponclosureoftheosteotomywedgeontheconvex
side.
RevisionSurgeryforInstrumentationFailureDueto
PostoperativeCoronalImbalance
Long spinal instrumentation is often indicated in adult spinal deformity, which
immobilizesalong spanofspinal segments,leadingto increasedmotionofthe adjacent
segmentsandthepotentialfor degenerativepathology.Becausethelumbosacraljunction
presentshighmechanicaldemand,ahighrateofcomplicationshasbeenwelldocumented
forlong fusionstothesacrum.One oftheimplant-related complicationsis rodfracture,
which is associated with the use of iliac screws or small-diameter rods, operating at
inappropriate fusion levels, resulting in postoperative coronal imbalance, and failing to
addresssagittalimbalance.
Postoperative coronal imbalance often requires additional revision surgery. In our
practice, theincidence of rod breakage is15% in adult spinaldeformitypatients (9/59)
witha minimumof2-year follow-up,particularlyin patientswithpostoperativeresidual
kyphosis. We speculate that rodfracturemaypartly result from overloaded mechanical
forces imposed on instrumentation in cases with postoperative coronal imbalance (Fig.
7.5).
The use of iliac screws might increase the risk of implant failure because of the
increasedstiffnessofthelumbosacralconstructs.Theexcessivestressofrodcontouringis
necessarytoconnectiliacscrewsandS1pediclescrews,butitcanleadtorodfracture.
22
In particular, we foundthat, in patients with postoperativecoronal decompensation, the
locationof therod fractureisoften closeto thelevel oftheiliaccrestor theosteotomy
level(Fig.7.6).
Postoperativecoronalimbalancethatiscomplicatedbyasymptomaticrodfractureisa
definitive indicationfor revision surgery. Severalmodalities have been employedtofix
the fractured rod. Traditionally, the entire incision is reopened and the fractured rod is
replaced with a new one. Alternatively, revision with a combination of in-line rod
connectors andcross-links can restorethe stiffness ofthe original constructwithout the
needtoreplacetheentireconstruct.Toreinforcethelocalconstructionofthefracturedrod
anddecreasetheriskofcomplications,weusesatelliterods(Fig.7.6).Thislocal direct-
repairstrategyrequiresthereopeningofonlytheareasurroundingthefracturedrodrather
than the entire opening along the instrumentation. More importantly, satellite rods can
enabletherestorationofcoronalbalancethroughlocalcompressionattheconvexsideor
distractionat theconcave side.Recently, we startedusing thesatellite rodsin theindex
surgery at the osteotomy level or when the instrumentation bridges the lumbosacral
junction.
ChapterSummary
Adult scoliosis may stem from the progression of scoliosis in children or adolescents
(idiopathic type), or may newly develop in adulthood through degenerative changes
(degenerativetype).Surgicalinterventions aremainlyindicated forpatientscomplaining
ofpainanddisability.Inourexperience,severalfactorsdifferentiatebetweendegenerative
and idiopathic scoliosis. In degenerative scoliosis, disk degeneration contributes to the
occurrence of spinal imbalance. Disk degeneration at the lower end vertebra strongly
correlates with sagittal imbalance, whereas that at the apex correlates with curve
magnitude.Indegenerativelumbarscoliosis,imbalanceinthecoronalplaneisfrequently
observed and usually associated with deterioration of symptoms such as back pain and
radiculopathy. A recent survey found a high rate of preoperative coronal imbalance in
degenerative lumbar scoliosis, on either the concave or the convex side. Corrective
surgerymightresultincoronaldecompensationinadultscoliosispatients,leadingtotrunk
shiftingandpossiblyimplantfailure.Deformity-andsurgery-relatedfactorsmightleadto
thiscomplication.
Fig.7.4a,b(a)A65-year-oldwomanwithdegenerativescoliosisandatypeCcoronalbalancepattern.Lumbarkyphosis
andseveresagittalimbalancewasnoted.Asperthesurgicalalgorithm, a long fusion from T6 to S1 was startedwith
osteotomyatL4/5 tobalancethespinein thecoronalplanefollowedby apediclesubtractionosteotomy(PSO)atL1.
(b)At2-yearfollow-up,thespinalbalancewaswellmaintained.
Fig. 7.5a–h (a,b) A 56-year-old woman with degenerative lumbar kyphoscoliosis complicated by lumbar stenosis.
Posterior spinal fusion from T5 to pelvis was done together with L4-L5 decompression. (c,d) Postoperativecoronal
imbalancewasnoted.(e)Bothrodswerefracturedat8months’follow-up.(f)Revisionsurgerywithadominoconnector
wasperformedtorestorecoronalbalance,whichwaswellmaintainedat(g,h)2years,follow-up.
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