Unstable Lumbar Spine

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386 Medical Progress August 2006

Unstable Lumbar Spine:Diagnosis and AssessmentMyung-Sang Moon, MD, PhD, FACS

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Instability is now considered one of themost important causative factors in lowback disorders. In recent years,emphasis has been increasingly placed

on the maintenance of segmental stability ofthe spine.1

Joint instability can result from variouscauses, and is classified by its tilt angleand/or translational displacement.1-5 Thisarticle provides a brief overview of thedefinition, pathogenesis, clinical featuresand diagnosis of unstable lumbar spine.

Definition

Segmental lumbar spine instability is a clini-cal concept. It differs from the mechanicaldefinition of stability and is difficult toassess.6-10 It refers to clinically excessive orinappropriate movements (wobbling) of amotion segment under load, either within orbeyond a normal range of movement, despitenormal ligamentous constraints. Instabilitymay also be defined as joint deformationwith stress.8,9

Newman defined instability as a loss ofintegrity of soft tissue intersegmental control,causing potential weakness and liability toyield under stress.8 The neutral zone of themotion segment is enlarged, within whichthe intervertebral discs and ligaments havelittle resistance to movement.1-5

The terms spinal flexibility, unstableback and weak back are sometimes used toexpress spinal mobility; the latter is a laymanterm and may not be synonymous withunstable back. Weak back may manifest aseasily fatigued back muscles, stiffness andweakness, accompanied by aching during or

after slight loading on the back.

Pathogenesis

Excessive axial rotation and translation ofthe lumbar spine may follow injury to theneural arch, including the facet joints (withor without facet joint asymmetry). Oncedegenerative changes occur in the interverte-bral discs, movement between adjacentvertebrae becomes uneven, excessive andirregular.

Figure 1. Spondylolisthesis at L3 due to congenital

absence of a pedicle.

Initial radiograms of the (A) anteroposterior; (B) neutral lateral; (C) forward flexion; (D)extension view;and (E) oblique view. (F) MRI. (G, H) Postoperation (pedicle screwfixation).

A B C D

E F G H


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Excessive range of movement isassociated with congenital (Figure 1)and/or acquired structural defectsand damage. (Table 1) Intervertebraldisc injury increases the size of theneutral zone. Loss of water in thenucleus, either as a result ofsustained loading or degenerativechanges, also decompresses the disc,slackens the annulus and reduces ro-tational stiffness, even when skeletalstability is normal. This may explainwhy repetitive shear and compres-sion loading causes a vertebra tocreep forward and rotate slightly. Onthe other hand, in the presence ofskeletal defect, the motion segmentswould also become unstablegradually despite normal ligamen-tous and muscular structures.

In severely unstable spine, thedisc and facet joints of the affectedsegment are degenerated. As aresult, the spinal canal and neuralforamen become narrowed due tohypertrophic bony spurs, andstenotic symptoms are resulted fromthe thickened ligamentum flavum.

The paraspinal muscles are posi-tioned to provide stability within theneutral zone, but only as far asangular rotations are concerned.

The back muscles are poorlyoriented to prevent small transla-tions. They can nevertheless affecttranslational stability indirectly bychanging the compressive forceacting on the spine: an abnormallylow compressive preload arisingfrom impaired muscle action wouldreduce impaction of the adjacentneural arches, thereby reducing thespines resistance to bending andaxial rotation. Inadequate localmuscle tone may similarly allowgreater translational movement, es-pecially if the disc is degenerated.

It is important to consider thecause of segmental instability in in-dividual cases, which can be neural(eg, acquired Charcot joint) or non-neural (eg, skeletal anomaly, isthmic

defect [Figures 2-4], pedicle defect[Figure 1]) in origin.

Classification

Table 2 and Figure 5 illustrate thevarious patterns of spinal instability.

In general, spinal instability isclassified by the directions and thedegree of displacement.11,12 There areseven types of angulatory and trans-lational instabilities, consisting of

basic (anterior, posterior, lateral,vertical and rotational) andcombined forms. Among these, an-gulatory, translational andcombined angulatory-translationalinstability in the sagittal and coronalplanes are the most common.8,13

True lateral translation has neverbeen reported in clinical settings,although lateral rotatory olisthesis isfrequently encountered in elderlypatients with degenerative lumbarscoliosis. Also, unlike vertical insta-bility, pure rotatory instability is notclinically observed.6,7,14,15

This simplified classification,however, may not suffice inproviding the necessary informationfor correctly diagnosing unstablelumbar and lumbosacral spines, and

to guide selection of surgical proce-dures. For this reason, I use aclassification that takes into accountalso the severity of instability andthe clinical symptoms and signs: The severity of angulation, trans-

lation and rotation; and The presence of central stenosis,

which can be further classified as(1) dynamic or static and (2)reducible or nonreducible.9,13

In some cases of dynamic central

Medical Progress August 2006 387

Table 1. Excessive range of movement and structural defects/damages

Excessive range of movement Causative structural defects/damages

Hyperflexion Posterior osseous-ligamentous injury/defect

Hyperextension Damage to the anterior ligaments

Neural arch damage/defect (including the apophysealjoint, articular surface and capsular ligament)

Excessive lateral bending Gross neural arch fracture/severe tear in theanterolateral annulus

Excessive axial rotation Neural arch damage/defect (including the apophyseal

joint, articular surface and capsular ligament) Gross neural arch fracture/severe tear in theanterolateral annulus

Figure 2. Polyarthriticdegenerative scoliosis in a

53-year-old woman.

Lateral rotatory slip of L2 and anterior slip of L3are seen.


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IN FOCUS

stenosis, symptoms can be relievedby flexion; whereas in others,symptoms can be relieved byextension with or without reductionof the slipped vertebral body. Thenonreducible type is considered anon-hypermobile instability, mani-festing the progression of thehypermobile segment to a near end-stage, when the degenerative andreparative processes have reached astatic equilibrium.

Other systems of classificationhave been proposed by Pope,Frymoyer and Krag, who havedivided segmental instability intoprimary and secondary types;4 andby Lee and Kopacz, who have classi-fied discogenic lumbar instabilityinto three major groups on the basisof the instability plane involved:sagittal plane instability, coronalplane instability and axial instabili-ty.12 An example of coronal planeinstability would be degenerativelumbar scoliosis. The conditionshould be differentiated from adultidiopathic scoliosis; in the former,there is advanced degenerativechange, lower lumbar curve, and

minimal structural vertebraldeformity. Radiologically it can befurther divided into two main types:oligoarticular and polyarticular.

Clinical Symptoms and Signs

Patients with an unstable lumbarspine complain mainly of low backpain, sciatica and/or claudication.Some may experience frequentepisodes of catching pain or acute

asymmetrical low back pain against abackground of chronic pain with orwithout leg involvement. This pain isautomatically accompanied by asym-metrical muscle contractions.

Pain is the most common earlysymptom of unstable lumbar spine,although it may also arise from anumber of structures within oradjacent to the spinal column. Thesestructures include the intervertebraldisc, zygapophyseal joints, vertebralbodies and surrounding ligamentsand muscles. In addition to muscu-loskeletal causes, pain can also resultfrom compression or damage to thenerve roots exiting from the spinalcanal, or to the spinal cord itself.

Table 2. Patterns of hypermobile instability

Abnormal motion (displacement) Plane of motion Degree of displacement

Translation Horizontal >2-3mm*

Anterior Posterior

Lateral (rotatory)

Angulation (angle of disc space or tilt) Sagittal >9**

Forward (flexion) Coronal L2-L3 14.3

Backward (extension) L3-L4 15.5

Lateral right L4-L5 18

Left

Rotation Axial Facet joint gapping

Right

Left

*Wiltse and Winter14; **Graf7; Dvorak.6

Figure 3. Postlaminectomyspondylolisthesis of L4.

Extension angular instability with anterior slip isseen. (A) Initial (spinal stenosis). (B) Immediatepostoperative radiograms. (C) Postoperative 6 yearsand 8 months.

Figure 4. Three types of lumbar

scoliosis with lateral rotatory

slips.

(A) Idiopathic scoliosis with hyperlordosis andL3 lateral rotatory slip. (B) Degenerative scoliosiswith L3 lateral rotatory slip and loss of lordosis.Vacuum sign is seen at L3-L4 disc in A-P view.(C) Post-laminectomy scoliosis with advanceddisc de-generation at L3-4 and L4-5, and anteriorslip of L4.

A B C

A B C


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Apart from back pain, patientswith degenerative lumbar scoliosisalso present with spinal deformitywith body tilt and rotatory slipand/or stenotic symptoms.

Diagnosis

While there are many modern diag-nostic modalities available, plainroentgenograms remain the key fordiagnosis. Simple and stress x-raysshould be used as the first step indiagnosing patients whose symp-

toms suggest unstable back.The diagnosis of clinical instabil-

ity of a spinal motion segment canbe established when pain isaccompanied by demonstrablehypermobility. Low back pain isusually divided into four groupsaccording to their probable origins.(Table 3) For a definite diagnosisof unstable back, the followingfindings must be present on plainradiograms: (1) angulatory and/or

translational displacement of avertebral body against an apposingvertebral body; (2) Hadleys lazy Ssign;16 (3) traction spur; and (4) theKnuttsons vacuum sign in the disc.17

(Figure 4) The latter sign, however,may have a higher detection ratewith CT scan (Lin, personal com-munication, 2006).

The exact cause of the unstableback and pain should be identifiedbefore commencing treatment.However, this may not be straight-forward. Angulatory instability canbe difficult to assess. Currently,there is no reliable diagnostic test toidentify rotational instability at itsearly phases, although manifestationof pain on axial rotation is highlysuggestive. Dynamic CT scan with

the patient twisting the trunk is alsouseful in the diagnosis (showingsigns of facet joint gapping). It ismandatory to take x-rays of the un-stressed and stressed lumbar spine inbending and twisting positions.7

The diagnosis is also difficult toestablish when the pain is caused bynon-hypermobile abnormal motionand/or abnormal biomechanicalresponse to a physiological loadingcondition.

The diagnosis of stenosis in anunstable spine depends mainly onclinical symptoms, with further prooffrom myelogram, CT myelogram andMRI. A CT scan using the twist-testtechnique can demonstrate gappingin a posterior joint with recurrentspinal nerve entrapment.7 MRI of thelumbar spine can show discal involu-tion as well as subchondral marrowchanges adjacent to a degenerativedisc. However, MRI changes are not

definitive.

References1. Panjabi MM, Goel RK, Takata K. Physiologic

strains in the lumbar spinal ligaments: An in vitro

biomechanical study. Spine 1982;7:192.

2. Pearcy M, Sheperd J. Is there instability in

spondylolisthesis spine? 1985;10:175.

3. Pope M, Panjab M. Biomechanical definitions

of spinal instability spine. 1985;10:255-256.

4. Pope M, Frymoyer JW, Krag MH. Diagnosing

instability. Clin Orthop 1992;279:60-67.

5. Strauss PJ, Novotmy JE, Wilder DG, Grosler LJ,

Pope MH. Multidirectional stability of the Graf

system. Spine 1994;19:965-972.

6. Dvorak J, Panjabi M, Chang D. Functional radi-

ographic diagnosis of the lumbar spine Flexion,

extension and lateral bending. Spine 1991;165:

562-571.

7. Graf H. Instabilite vertebrale. Treatment a

1aide dun system soule. Rachis, 1992.

8. Moon MS. Treatment of unstable lumbar spine

with Graf band system. Presented at 19th World

Congress, SICOT, Aug. 30, 1993.

9. Moon MS, Moon YW, Moon JL, Kim SS, Shim

YS. Treatment of flexion instability of lumbar spine

with Graf band. J Musculoskelet Res 1999;3:49-63.

10. Kirkaldy-Willis WH, Farfan HF. Instability of the

lumbar spine. Clin Orthop 1982;165:110-123.


Translation

Flexion

Extension

Normal(neutral lateral)

Angulation andtranslation

Angulation

Figure 5. Patterns of spinalinstability. Table 3. Classification of low

back pain

Group I Radiculopathy and spinal

stenosis

Group II Anterior column origin ordiscogenic pain associated withdegenerative disc disease orspondylolisthesis

Group III Posterior column pain includingthe facet joints

Group IV Back pain of soft tissue origin*

*Generally a non-surgical condition.

About the AuthorDr Moon is Professor Emeritus at the Catholic

University of Korea, Director of the Moon-

Kims Institute of Orthopedic Research, Seoul,

and Spine Center, Sun General Hospital,

Daejeon, Korea. Dr Moon is currently President

of the Asia Pacific Orthopaedic Association.

E-mail: [email protected]

A complete list of references can be obtainedupon request to the editor.


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IN FOCUS

Unstable Lumbar Spine:ManagementMyung-Sang Moon, MD, PhD, FACS

T

his article discusses some of themanagement issues regardingunstable lumbar spine, with a brief

review on its surgical treatmentoptions. It needs to be stressed that, however,the treatment for painful unstable backremains poorly defined, and disagreementexists as to when surgery is indicated in lowback pain that appears to be originatingfrom spinal structures.

Management Principles

A suggested treatment algorithm for clinicalinstability is outlined in Figure 1. Some

general management principles are as follow: Even when unstable low back is diag-

nosed, stabilization should not be started

until the origin can be confirmed.1

In patients with persistent disabling lowback pain, deteriorating stability and/orno signs of spontaneous stabilization,bracing and movement restriction shouldbe done to stabilize the segment.

When conservative treatment fails, sur-gery is indicated.

Sufficient time must be given for the trialof conservative treatment to adequatelydetermine the patients clinical responseand the next treatment.2,3

Figure 1. Treatment chart for clinical instability.

Diagnosis ofclinical instability

Courseof

disease

Bracing and observe

Treatment notrequired

(Watchfulwaiting)

Stabilizationsurgery

Is there associatedpain at diagnosis?

Pain persisted?

Static equilibrium

No

No

Yes

Yes


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IN FOCUS


Unstable Back Without StenoticSymptomsIn unstable lumbar spine withoutstenotic symptoms, conservativetreatment aims at reducing the stresson the unstable segment to halt dete-rioration and minimize pain. Rota-tion appears to be the most harmfulmotion, since it creates both com-pression and shear, and should beavoided. Patients should be advisedto avoid certain activities, and train-ing programmes can be provided toimprove posture and strengthen backmuscle. (Table 1) In obese patients,especially men, the increased weightaround the abdomen worsens lordo-sis, and weight reduction should beadvised.

With proper conservative care,time alone will reduce hypermobilityand improve long-term stability.

Unstable Back With SymptomaticStenosisIn these patients, the stenotic symp-toms should be relieved by all means,conservatively or surgically. Thisshould be done prior to the treatmentof instability, regardless of the cause.

Tables 2 to 5 list the availablemotion-preservation, -restrictionand -elimination (fusion) surgicaloptions and nerve decompression

procedures for the management ofunstable back with symptomaticstenosis. The following should beconsidered when planning fortreatment: Instrumented stabilization gener-

ally relieves pain completelyexcept in a few cases.

While spinal stabilization surgerycan relieve musculoskeletal painin trauma-related cases, it maynot be useful for pre-existing neu-ropathic pain.

For dynamic stenosis, flexion-dis-traction or extension-distractionfusion without decompressivelaminectomy can theoreticallyrelieve stenotic symptoms. How-ever, flexion-distraction fusion isnot preferred because it misalignsthe sagittal lumbar curvature (ie,making the back flat).

In static stenosis, decompressivelaminectomy with or withoutfacetectomy should be done,followed by stabilization surgery.

Extensive decompressive laminec-tomy should always be followedby stabilization surgery, becausethe former further destabilizes theunstable decompressed segment.This holds true even in patientswith non-hypermobile instability.

In the case of posterior column

defect, posterior stabilization sur-gery is indicated, whereas anteriorstabilization surgery is indicatedfor anterior column defect.

Facet rhizotomy is contraindi-cated because it denervates themultifidus and increases hyper-mobility and instability.

Stabilization Surgery

Stabilization surgery for sympto-matic unstable spine aims at spinalrestoration by reinforcing the defi-cient ligamentous and bony struc-tures, in order to normalize thespine-spinal nerve relationship. Thisis done by stabilizing the spinal unit,restoring normal alignment and cor-recting deformity, and/or decom-pressing the nerves. Figure 2 showsthe various treatments for differenttypes of instability.

Table 1. Posture and exercise suggestions for patients without stenotic

symptoms

Avoid activities such as shovelling, lifting and gardening.

Avoid sports such as handball, squash, tennis and cycling.

Avoid standing on one leg, as it produces asymmetrical stress on the pelvis and spine.

Isometric, abdominal and low back exercises that work primarily on the deep muscles of theback/the multifidusstabilize the back and improve balance.These exercises are best done onexercise mats.

Physiotherapy with a back muscle training programme and lifting technique training arebeneficial.

Table 2. Motion-preserving

stabilization surgeries

1. Direct osteosynthesis of lytic isthmus

with screwing and bone graft

2. Scott wiring for direct repair

3. Combined stabilization surgery

Table 3. Motion-restriction

surgeries

Type of instability Procedure

Flexion instability Ligamentoplasty1.Grafs procedure2.Mochidas

procedure

Extention instability Interspinous softcushion spacer

1.Silicone device2.Metal device


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Stabilization surgery of the spinefollows the basic mechanics of thespine. The spine has two mobilecolumns, the anterior and posteriorcolumns. In the anterior column,motion is transferred through the

disc in relation to its elasticity, whilein the posterior column motion istransferred through the facet joints.Load sharing between these twocolumns maintains spinal integrity.The architecture of the spine is sodesigned as to resist anteriorlyagainst compression and torqueforces, and posteriorly againsttension forces. The muscles andligaments exert posteriorly compres-sion forces. The tension band

principle therefore suggests that instabilization surgery, a posterior in-strumentation should act as acompressive device.

In the following discussion, wewill consider the common proce-dures for sagittal and coronal spinalinstability (degenerative scoliosis).

Stabilization Surgery for SagittalInstabilityMotion-restriction (Non-fusion)SurgeryFor forward flexion sagittal instabil-ity, two ligamentoplasty proceduresare available: Graf ligament stabi-lization procedure and the posterior

ligamentoplasty described byMochida et al. Graf ligament stabilization is a

re-enforcement, band fixationprocedure for inefficient poste-rior stabilizer. The Graf artificialligament serves as a tension bandto suppress firstly excess flexion,and secondly rotation, by appos-ing or locking the facet joints inlordosis. The procedure is indi-cated only in pure forward flex-

ion instability, and should not beused in the presence of extensioninstability secondary to anteriorstabilizer inefficiency or failure.With the posterior stabilizationprovided by the pre-stressed, flex-ible Graf ligaments, facet jointgapping can be eliminated, whichis the major source of pain. It alsorestores normal lumbar lordosis,which repositions the stabilizedjoint so that exposure to rotativemechanical aggression is mini-mized. Graf ligament fixationshould not be used in cases withanterior, posterior and rotatorycorporal translation with poste-

rior angulation.2,3 In cases of lat-eral canal stenosis, completeunroofing of the lateral canal ismandatory, because bandingcauses extension and compres-sion to the applied segment,which in turn causes narrowingof the neural foramen.

In the posterior ligamentoplastydescribed by Mochida et al, artifi-cial ligaments are used to stabilizethe posterior element through the

Table 4. Motion-elimination

surgeries

1. Posterior stabilization surgery

Posterior fusion ( posterior

instrumentation) Posterolateral fusion ( posterior

instrumentation)

Posterior interbody fusion

Transforaminal interbody fusion

2. Anterior stabilization surgery

Anterior interbody fusion anterior

instrumentation

3. Combined anterior and posteriorfusion anterior and/or posteriorinstrumentation

Table 5. Nerve decompression

procedures

Laminotomy

Foraminotomy

Combined extensive laminectomy and

foraminotomy

Facetectomy

In situ or post-reduction fusion

Translation

Normal(neutral lateral)

Angulation andtranslation

Angulation

Anteriorstabilization

Posteriorstabilization





or

Extensioninstability

Extension instability

Flexion instability

Flexioninstability

Translationalinstability(discogenic)

Figure 2. Stabilization surgery for different types of instability.


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pedicles. The problem with thisprocedure is that the ligamentfixation area is too close to thespinal flexion axis, and provisionof proper ligament tension is dif-ficult. Some authors thereforesuggested that the procedure isnot beneficial in re-enforcing theinefficient posterior stabilizer.Also, compared with the Grafband, material creep may be aproblem with this procedure,

undermining its usefulness in pro-viding long-term posterior stabil-ity without failure.2-4

For extension sagittal instability,interspinous soft cushions are nowavailable for stabilization surgery.5,6

These devices prevent furtherextension of the instrumentedsegment from its neutral position.This helps to maintain a widerforaminal space and prevent the de-velopment of symptoms secondary

to dynamic extension and stenosisof the segment.

Motion Elimination (Fusion)SurgeryBased on the tension band principlementioned above, some authors haverecently argued that a secure fusionrequires combined anterior and pos-terior instrumental stabilization.However, this is still debated.

Posterior procedures include

posterior fusion, posterolateralfusion and posterior lumbarinterbody fusion. The latter two arethe more popular procedures, andcan be done with or withoutposterior instrumentation. Forspinal instability with preservedanterior load sharing, pedicle screwfixation alone provides sufficientstability, and interbody cages shouldnot be used, because they furtherincrease segmental motion in the

adjacent segment.7 When theanterior column is deficient,however, the use of interbody cagessignificantly increase constructstiffness and decrease hardwarestrain. For axial rotatory instability,derotation facet fusion is indicated.8

The procedure alone should decom-press the nerve roots. However, thecurrent trend is to supplement itwith transverse process fusion andinstrumented stabilization, after sta-

bilizing the unstable segment withderotation facet fusion.

Anterior procedure involvesanterior lumbar interbody fusionwith or without instrumentation.(Figures 3 and 4) Both in situ andpost-reduction fusions are wellaccepted for oligoarticular spinaldisorders with instability. Anteriorlumbar interbody fusion can be usedin cases of sagittal translationalinstability without neurological

Figure 3. Isthmic spondy-lolisthesis at L4 without

neurological involvement in a

54-year-old man.

(A) Preoperation. (B) After anterior interbody fusion.

A B

Figure 4. Isthmic spondylolisthesis at L5 in a 13-year-old girl with severeback muscle spasm and markedly limited straight leg raising.

(A) Preoperation. (B) Immediate after posterior instrumentation. (C) After anterior interbody fusion at L5-S1.(D) Postoperation 1 year. (E) Postoperation 6 years. Solid anterior fusion at L5-S1 is seen.

A B C D E


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symptoms. In such cases, intertrans-verse fusion is also indicated, whichcan be supplemented by posteriorinstrumentation.

Stabilization Surgery for CoronalSpinal InstabilityTwo types of fusion procedures,poly-articular and oligoarticularfusion, are available for coronalspinal instability (degenerative lum-bar scoliosis). Depending on the clin-

ical types, surgical management maydiffer: In cases with neurological com-

promise, decompression surgeryshould precede the combined cor-rective and fusion operation.

In case with symptomatic pro-gressive degenerative scoliosiswithout stenotic symptoms,fusion supplemented by internalfixation after complete correctionof coronal deformity and sagittalalignment is the most appropri-ate.

In fusion surgery for the scolioticspine, deformity correctionshould be included, because inmost cases undercorrection ofcoronal deformity would compli-cate junctional instability.

For painful, unstable degenera-tive lumbar scoliosis withoutrotation and stenotic symptoms(localized to 1-2 joints), anteriorlumbar interbody fusion is rec-

ommended. For stable, nonprogressive, poly-

articular degenerative lumbarscoliosis with stenotic symptoms,decompression surgery alonewould suffice.

For unstable degenerative lumbarscoliosis with stenotic symptoms,instrumental stabilization of theentire scoliotic segment aftercomplete decompression anddeformity correction is preferred.

Nerve Decompression Surgery forStenosisPosterior DecompressionPosterior decompression involvesposterior unroofing of the centraland/or lateral canal. It is the proce-dure of choice for unstable degener-ative lumbar spine with stenoticsymptoms, regardless of the associat-ing deformity. However, since thisprocedure further destabilizes thespine, it should be combined with

stabilization surgery.

Anterior DecompressiveCorpectomyThis procedure is in general not indi-cated in the treatment of unstablelumbar spine with stenosis. Even instatic stenosis, anterior lumbar inter-body fusion alone would suffice, as itreduces and realigns the slippedvertebra, thereby stabilizing thefused segment and relieving stenoticsymptoms.9

Posterior Instrumented ReductionPosterior instrumented reduction forlateral and vertical displacement, ordisc migration, restores the centralcanal size and spinal alignment,thereby decompresses the entrappednerves. However, decompressionmay not always be achieved withthis procedure.

Fusion in the Flexion-distraction or

Extension-distraction PositionA proper position for fusion isimportant in relieving stenosissymptoms. Fusion in the flexion-distraction or extension-distractionposition effectively relieves dynamicstenosis symptoms and providesstability at the same time.

In cases of retrolisthetic instabili-ty at L5, which is frequentlyassociated with lateral spinal canalstenosis affecting the S1 nerve root,


IN FOCUS

fusion in flexion (with distractionrods, pedicle fixation devices andfacet fusion) is the treatment ofchoice.

In general, during spinal fusion,an internal fixation system shouldbe used as an adjunct to stabilize thefusion segment and to maintain thefusion position.

Prognostic Factors

The prognosis of unstable back willdepend on the patients age and sex,the degree of disc degeneration, bonyand facet configuration and defect,traction and claw spurs, lumbosacralangle, and height of L4 in regards tothe intercrestal line.

Prognosis is generally good ifsigns of symptom relief and radio-logical improvement can beobserved during the course of stabi-lization. Clinical symptoms shouldgradually subside towards the endstage of instability when the staticequilibrium is reached. Radiologi-cally, gradual decrease of motionshould be demonstrated with thestress test, with no further collapseof disc height. Formation of anterioror lateral bony buttress should beseen in the upper margin of thelower body.

About the AuthorDr. Moon is Professor Emeritus at the Catholic

University of Korea, Director of the Moon-

Kims Institute of Orthopedic Research, Seoul,

and Spine Center, Sun General Hospital,

Daejeon, Korea. Dr Moon is currently

President of the Asia Pacific Orthopaedic

Association.

E-mail: [email protected]

A list of references can be obtained upon

request to the editor.

Answers to questions on page 385: 1. T 2. F 3. F 4. T 5. T

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Unstable Lumbar Spine