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Fig.2.7a–eA71-year-oldmanwithcomplaintsofaxialbackpainandbilaterallowerlimbclaudication.(a)Thepatient
hasdegenerativescoliosisfrom L3 toL5,withaCobbangleof 25 degrees.(b)L3–4 and L4–5 spondylolisthesis and
spinalstenosiswerenoted.(c)TheL5-S1waswellhydrated,andtherewasnoobliquetake-off.(d,e)Shortfusionfrom
L3toL5wasperformedwithgoodcorrectionofthesegmentalinstability.
Fig. 2.8a–d A 58-year-old man with axial back pain and lumbar hypolordosis. There is (a) an oblique L5-S1 with
degenerativechangesand(b)apositivesagittalimbalance. (c) The patientwastreatedwithanL3pediclesubtraction
osteotomyandposteriorspinalfusionfromT10tothesacrumwithS1andiliacinstrumentation.(d)Goodrestorationof
sagittalbalanceisobservedpostoperatively.
UpperInstrumentedVertebraforLongFusions
In general, forlong fusions, the authors’preference is to end at T10or above, because
instrumentation and fusions ending at T12 to L1 have been shown to have a higher
revisionrate,likelyrelatedtothehypermobilethoracolumbarregionasittransitionsfrom
an immobile thoracic spine to a mobile lumbar spine. There are also changes in facet
orientation from coronal to sagittal and changes in sagittal alignment from kyphosis to
lordosis.ExtendingtheUIVtoT10(levelwithtrueribs)orfurtherproximallycanprovide
relativeprotectiontotheadjacentsegmentwiththeincreasedstabilityprovidedbytherib
cage.Theribcagelengthensthetransversedimensionsofthespineandgivesthethoracic
spinegreaterresistancetobendingstressesinmultipleplanes.T11orT12doesnothave
costosternal articulations; hence, these levels lack the biomechanical advantage of the
upperlevels.
Inaddition,otherfactorsthatcouldaffectlong-termsurvivalofthatsegmentneedtobe
takenintoconsideration. Thesefactorsincludehealthyadjacentspinalsegments withno
degeneration or instability in any plane, and a UIV adjacent to spinal segments with
normalsagittal,coronal,andaxialalignmentandnear-neutralrotation.TheUIVshouldlie
withinthe“stablezone”definedbythecentersacralverticalline,beforesurgery,orcould
beplacedintothatzoneaftersurgery.
Currently,thereisnoconsensusstudyavailabletorecommendT10instrumentationin
all patients to improve long-term results. Disadvantages of the UIVabove T10 include
increasedriskofperioperativecomplications, andwithlongerinstrumentationacrossthe
thoracolumbarspinethere isalsoagreater riskofpseudarthrosis.Thus, therationalefor
stoppingat T10maynot beapplicablein allcases.Important decisionsonthe extentof
instrumentationandfusionshoulddependonthepositionoftheUIVinrelationshiptothe
globalspine.AnextensiontoT5orevenhigherwoulddependontheabilityofthelumbar
surgery to correct the sagittal imbalance. With control of more spinal segments, better
sagittalbalancemaybeachievedmoreeasily.
Ultimately,thesurgicalprocedureshouldbetailoredtoeachpatient’sneedsandbased
on the goal of achieving a well-balanced, stable, painless, and durable spine with the
fewestnumberoffusedsegmentswhilereducingtheriskofcomplicationsassociatedwith
large-scaleoperations.
LowerInstrumentedVertebraforLongFusions
For the lower instrumented vertebra (LIV), most long fusions will extend to the
sacropelvisorstopatL5.Inadolescentidiopathicscoliosis,itmaybepossibletostopat
L3orL4inalumbarcurve,butbecauseofstructuralchangesandafixedtiltfoundatthe
caudalspinalsegmentslikeL4-L5inadultdeformity,stoppingatamorecranialsegment
is generally not advised. Stopping at L5 enables retention of the lumbosacral motion,
avoidance of sacroiliac (SI) joint stress, decreased operative time and instrumentation
complications,andalowerpseudarthrosisrate.Pelvicfixationcanalsobeavoided.Onthe
otherhand,thisprocedureplacesalotofstressattheL5-S1disk,beingtheonlyresidual
mobilesegment,andthepatientneedstobewarnedoffuturebreakdownandtheneedfor
surgery to fuse this segment. In general, for many patients, the L5-S1 disk is already
degenerated,andinsuchcasesitisprobablybettertofusetothesacrum.Preservationof
theL5-S1diskenablessomepelvicmotion,whichmaybeimportantforsomefunctional
demandsofpatients,suchasridingabicycle.
Fusion tothe sacrumisrequired fordiskdegeneration atL5-S1, spondylolisthesis or
spinalstenosisatthe samesegment,aswellas obliquetake-offatL5-S1orinfractional
curvesgreaterthan15degrees.
22
Balancingisdifficultwithoutfusiondowntothesacrum
in cases of oblique take-off at L5-S1. In addition, the foramen is smaller on one side,
leadingtounilateralL5radiculopathy.Itisnotuncommontoseepatientswithforaminal,
central, or lateral recess stenosis at L5-S1. If stenosis is present at L5-S1 and more
extensivedecompressionisrequired,fusingdowntothesacrumisinevitable.Theobvious
disadvantages of fusion to the sacropelvis include increased operative time and more
extensive surgical dissectionto reach thesacrum. Anterior columnsupport may alsobe
required to reduce the rate of pseudarthrosis. Lost motion at L5-S1 may also alter the
patient’sgait.
Osteotomiesmayberequirediflessthan30%deformitycorrectioncanbeobtainedon
bendingradiographs.Thisisnotuncommonbecauseadultdeformitiesareusuallystiff.To
avoid overloading the instrumentation at the metal–bone interface, releases and
rebalancing would be required. There are two types of sagittal imbalance in adult
deformity.First,thespineisgloballybalancedbutasegmentalportionofspine isflator
kyphotic.Second,thereisglobalandsegmentalimbalance.Coronalimbalancecanalsobe
classifiedintotwotypeswiththeshouldersandpelvistiltedinoppositedirectionsorwith
tilting in the same direction. Posterior column osteotomies are the best choice for
segmental imbalanceof the spine. Aprerequisite would be mobiledisk spaces toallow
extensioncorrection.Ifthedisksarealreadydegeneratedandstiff,anteriorreleaseisalso
required.Ifthebonestockisinadequate,anteriorstructuralgraftscanbeusedtoimprove
fusion rates. For global imbalance, both Smith-Petersen and pedicle subtraction
osteotomiescanbeused.Typically,aSmith-Petersenosteotomyisindicatediftheweight-
bearing line falls within 3 cm of the sacrum, and a pedicle subtraction osteotomy is
reserved for cases with poor bone stock, and it can provide 30 degrees of lordotic
correction.Inpatientswith combinedcoronalandsagittalimbalance, pediclesubtraction
osteotomiesareaviableoptioniftheshouldersandpelvisaretiltedinthesamedirection,
butavertebralcolumnresectionisthebetteroptioniftheshouldersandpelvisaretiltedin
oppositedirections.
Anterior procedures are required only in rigid deformities that are not passively
correctable with posterior instrumentation. They are usually used only in combination
withposteriorinstrumentation, asinterbodyfusionsalone maynotbeable tocorrectthe
overall sagittal alignment.
23
Anterior spinal fusion can further correct lumbar
hypokyphosis and imbalance, provide indirect decompression by foraminal distraction,
prevent posterior instrumentation failure by load sharing, and decrease the rate of
pseudarthrosis, which is especially common in smokers, diabetics, and osteoporotic
patients.
14
Complications
Adult deformity surgery is challenging, and there are many associated complications.
Reported complicationrates reach 80% for adultdeformity,with up to 58%of patients
requiringreoperation.
15,16
Thesedegenerativeconditionsusuallyoccurintheelderlywith
multiple comorbidities such as pulmonary and cardiac disease, osteoporosis, and
nutritionaldeficiency.Theseconditionsshould beproperlyoptimized priortosurgeryto
decrease perioperative risks. Any of the above comorbidities may affect the timing of
surgeryaswellasthescaleofsurgicalcorrection.
Deformitycorrectioncanindirectlydecompresstheneuralstructuresbyrodderotation,
cantileverreductionmaneuvers, andparticularlybyincreasing vertebraldiskheightwith
anteriorinterbodyfusion.Overdistractionontheconcavesidemayleadtolossoflumbar
lordosis.Toreducerigidcurves,posteriorcolumnosteotomiesatmultiplelevelsarelikely
required to mobilize the spinal segments. Fusions should avoid stopping at a level of
rotatorysubluxationtopreventaggravatingthesubluxation.
With limited instrumentation and fusion, degeneration may be accelerated in the
remainingcurveas aresult of adjacentsegment disease. Stoppingthe fusionwithinthe
deformity may provoke these adjacent segment problems. Stopping the fusion at the
thoracolumbarjunction alsoleadsto adjacentsegment diseasecranial tothe segmentof
fusion.FusiontoT10orabovemayavoidthis.However,someconsideradjacentsegment
degenerationunpreventableinfusionsurgeryasitcouldbeduetothenaturalage-related
progression of a degenerative process coupled with the postsurgical effect of spinal
stiffeningcreatedbyfusionorinstrumentationprocedures.
24,25
Proximaladjacent segmentdegeneration isdetected byprogressivenarrowing ofdisk
height, progressive decrease in lordosis or increase in kyphosis, osteophyte formation,
sclerosisofanadjacentendplate,ortranslationinthecoronalorsagittalplanes.Proximal
junctional problems such as adjacent segment degeneration, compression fracture, or
screw failure in the UIV occurs more frequently with fusions ending at T11 to L2 as
comparedwiththoseatT10orabove.
26
FortheLIV,dependingonfusion toL5 ortothesacrum,differentcomplicationsmay
occur,includingL5-S1diskdegeneration,lossofcurveandbalancecorrection,iliacscrew
implantproblems,andpseudarthrosis.Ifthefusionis stoppedatL5wherethere isfixed
sagittal imbalance and disk degeneration at L5-S1, the rate of disk degeneration will
further increase, leading to loss of sagittal profile correction and L5-S1
spondylolisthesis.
22
Inosteoporoticbone,fusiontoL5has ahighriskoffixationfailure,
astheL5pediclesaremostlycancellousandtherearetrajectoryproblemsinobtaininga
medialangleforplacingthepediclescrews.FailureofL5screwswithlooseningleadsto
kyphosis or hypolordosis of the L4-L5segment.L4-L5 kyphosis may be tolerated in a
shortfusion,butwithlongerfusionsthedegreeofsagittalimbalancebecomesanissue.
FusionstothesacrumshouldbereservedforL5-S1spondylolisthesis,stenosis,oblique
take-off,moderate orsevereL5-S1 degeneration,and priorlaminectomy.Problemswith
long fusions to the sacrum include higher complication rates due to a large-scale
operation, risk of sacroiliac joint degeneration, altered gait mechanics and increased
pseudarthrosis.Instrumentationcomplicationsfortheselongfusionsincludebreakageand
back-outorlooseningofscrews.Toavoidthis,S1screwsshouldbebicorticalthroughthe
promontoryanteriorly.S1screwsshouldalsobedirectedmediallytoavoidpenetratingthe
L5nerveroot.BonegraftinganteriortoL5-S1andiliacscrewsmayfurtherprotecttheS1
fixation.ToimprovetheL5-S1fixation,distalhooks,iliacscrews,andinterbodycagesfor
anteriorcolumn supportare alsooptions. Hooksare analternative fixationespecially in
osteoporoticbonebutmaycausestenoticproblemsatL5-S1.
Iliacscrewsentailtheriskofpullout
27
andareusuallymoreprominent.Screwsshould
beburied ifpossible,but, inthinpatients, removalmaybe requiredandshould bedone
around 2 years after fixation. Technically, iliac screws are more difficult to insert with
previousposterioriliacboneharvesting.Thereisalsoahigherpseudarthrosisrateat L5-
S1, but this may be salvaged by revision surgerywithanterior reconstruction and iliac
fixationaswellasusingbonemorphogeneticproteintoimprovefusionrates.Thelowest
pseudarthrosisrateofL5-S1fusionsisassociatedwithcompletesacro-pelvicfixationand
surgeryinpatientsyoungerthan55yearsofage.
28
ChapterSummary
Inadultdeformity,thereisdifficultyinmatchingapatient’ssymptomsandconcernswith
the surgical plan. Clinicians must weigh potential gains and risks, and all surgical
decisionsshouldbeindividuallytailoredtothepatient.Comorbiditiesshouldbeaddressed
priortosurgerytoavoidperioperativecomplications.Usually,thesurgicaloptionsinclude
decompression alone, decompression with limited arthrodesis, and deformity correction
withlongfusion(Table2.1).Decompressionsurgeryisreservedforpatientswithlegpain
butminimalornobackpain,scoliosisCobbangleslessthan30degrees,lessthan2mmof
subluxation,nothoracichyperkyphosis,andacceptablecoronalandsagittalbalance,orif
theyhavea poorpremorbidstate.For shortfusions,patientsshould havescoliosisCobb
angleslessthan30degrees,segmentalinstability(morethan2mmoflateralsubluxation),
backandlegpain,nosignificantimbalanceissues,and,ifdestabilizing,decompressionis
requiredfor adequatereliefof spinalstenosis andnerveroot compression.Long fusions
are reserved for scoliosis Cobb angles greater than 45 degrees, more than 2 mm of
subluxation, and coronal and sagittal imbalance. To avoid complications related to
instrumentation, fusion should not end at a level with junctional kyphosis or
spondylolisthesis,posteriorcolumn deficiency,a rotated segment,a level atthe apex of
the deformity, or a degenerated level. Levels of rotatory subluxation must be included
within the fusion block. For balance, the most horizontal vertebra should be the UIV.
ExtensionofthefusiontoT10providestheincreasedstabilityofferedbytheribcage.The
LIVat L5isonly feasiblewith anormal L5-S1disk,and nospondylolisthesis orspinal
stenosisorobliquetake-offatL5-S1.Fusionstothesacrumshouldbeavoidedifpossible
toavoidiliacscrew implantproblems,pseudarthrosis,sacroiliacjointproblems,and gait
disturbances, but is usually mandatory for long-standing sagittal and or coronal
imbalances.
Pearls
Allsurgicaldecisionsfordegenerativescoliosisshouldbeindividuallytailoredtothepatient.
Decompressionsurgeryisreservedforpatientswithlegpain,minimalornobackpain,scoliosisCobbanglesless
than 30 degrees, less than 2 mm of subluxation, no thoracic hyperkyphosis, acceptable coronal and sagittal
balance,orthosewithpoorpremorbidstate.
ShortfusionsareforscoliosisCobbangleslessthan30degrees,segmentalinstability,backandlegpain,andno
significantimbalanceissues.
LongfusionsareforscoliosisCobbanglesgreaterthan45degrees,morethan2mmofsubluxation,andcoronal
andsagittalimbalance.
ExtensionofthefusiontoT10providesincreasedstabilityofferedbytheribcage.
ThemosthorizontalvertebrashouldbetheUIV.
Pitfalls
Fusion should notendat a levelwithjunctional kyphosis or spondylolisthesis,posteriorcolumn deficiency,a
rotatedsegment,attheapexofthedeformity,oradegeneratedlevel.
AvoidtheLIVendingatL5withanabnormalL5-S1disk,spondylolisthesis,spinalstenosis,orobliquetake-off
atL5-S1.
Fusionstothesacrumshouldbeavoided if possible due to the increased riskofiliacscrewimplantproblems,
pseudarthrosis,sacroiliacjointproblems,andgaitdisturbances.
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