Interspinous Fixation in the Stable Motion Segment

111Department of Neurosurgery, University of Michigan Medical SchoolDepartment of Neurosurgery, University of Michigan Medical School

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Interspinous Fixation in Interspinous Fixation in the Stable Motion Segmentthe Stable Motion Segment

Frank La Marca M.D.Associate Professor of Neurosurgery, Orthopedics and Biomedical Engineering,

Director of the Spine Program,

DepartmentDepartment of Neurosurgery

University of Michigan, Ann Arbor MI, USA


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Degenerative Disease OverviewDegenerative Disease OverviewBasic BiomechanicsBasic Biomechanics

• The The motion segmentmotion segment is the functional is the functional unit of the spine and consists of:unit of the spine and consists of:– Adjacent vertebrae Adjacent vertebrae – Ligaments (passive restraints)Ligaments (passive restraints)– Muscle (motion activators)Muscle (motion activators)– A 3 “joint” complex of two facet A 3 “joint” complex of two facet

joints and the disc (which is a joints and the disc (which is a unique type of “joint”)unique type of “joint”)

• DegenerationDegeneration can begin in one or more can begin in one or more of these “joints”, but ultimately all of these “joints”, but ultimately all three will be affectedthree will be affected


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Spinal StenosisSpinal Stenosis• Narrowing of the spinal canal Narrowing of the spinal canal

and/or lateral foramen through and/or lateral foramen through which the nerves travelwhich the nerves travel

• Three types:Three types:– Central stenosisCentral stenosis: in central : in central

spinal canal where spinal cord spinal canal where spinal cord or cauda equina are locatedor cauda equina are located

– Lateral recess stenosisLateral recess stenosis: in the : in the corners where nerve roots corners where nerve roots travel before exiting canaltravel before exiting canal

– Foraminal stenosisForaminal stenosis: in lateral : in lateral foramen where nerve roots foramen where nerve roots exitexit


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Lateral Recess Stenosis-TreatmentLateral Recess Stenosis-Treatment


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Lumbar Spinal StenosisLumbar Spinal Stenosis

• Neurogenic Claudication:Neurogenic Claudication: Thigh pain increases with Thigh pain increases with walking /standingwalking /standing– Relief with flexing forward Relief with flexing forward


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Spinous Process Fixation and Spinous Process Fixation and Distraction DevicesDistraction Devices

Theoretic advantagesTheoretic advantagesEase of placement, flat learning curve, rapidly Ease of placement, flat learning curve, rapidly

deployed.deployed.Minimize risk to neurovascular structuresMinimize risk to neurovascular structuresEasily revised (no bridges burned)Easily revised (no bridges burned)

Potential disadvantagesPotential disadvantagesLimits decompressionLimits decompressionSuboptimal fixation rigidity?Suboptimal fixation rigidity?Loosening under repetitive cycling?Loosening under repetitive cycling?Potential for overuse?Potential for overuse?


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Spinous Process DevicesSpinous Process Devices• Historical perspectivesHistorical perspectives

– Wiring techniquesWiring techniques– Rigid FixationRigid Fixation

• Daab, Wilson platesDaab, Wilson plates• Renewed interestRenewed interest

– Interspinous spacers Interspinous spacers • X-stopX-stop

• Contemporary SP fixationContemporary SP fixation– Spire (Medtronic) Spire (Medtronic)

• Wang et al. J Neurosurg Spine 4:132-136, 2006Wang et al. J Neurosurg Spine 4:132-136, 2006• Wang et al. J Neurosurg Spine 4:160-164, 2006Wang et al. J Neurosurg Spine 4:160-164, 2006

– Aspen (Lanx), NuvasiveAspen (Lanx), Nuvasive


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Aspen Device Indications - EUAspen Device Indications - EU• The Aspen Spinous Process System is a spinous process fixation device intended to The Aspen Spinous Process System is a spinous process fixation device intended to

provide stabilization in the thoracic, lumbar and sacral spine (T1—S1). It can be provide stabilization in the thoracic, lumbar and sacral spine (T1—S1). It can be used as an adjunct to interbody and/or posterior fusion or as a standalone fixation used as an adjunct to interbody and/or posterior fusion or as a standalone fixation device. The Aspen Spinous Process System is indicated in the treatment of the device. The Aspen Spinous Process System is indicated in the treatment of the following conditions:following conditions:• Degenerative disc diseaseDegenerative disc disease• Spinal stenosisSpinal stenosis• SpondylolisthesisSpondylolisthesis• Trauma (e.g. fractures, dislocation)Trauma (e.g. fractures, dislocation)• Spinal deformities (scoliosis, kyphosis, lordosis)Spinal deformities (scoliosis, kyphosis, lordosis)• Spinal tumorsSpinal tumors• Pseudoarthrosis or failed previous fusion surgeryPseudoarthrosis or failed previous fusion surgery• Spinal instabilitySpinal instability

• The Aspen Spinous Process System can be used in single- or multi-level constructs. The Aspen Spinous Process System can be used in single- or multi-level constructs. It can be used alone or in combination with other spinal devices (e.g. pedicle screws, It can be used alone or in combination with other spinal devices (e.g. pedicle screws, facet screws, anterior plates or interbody cages). The ASPEN Spinous Process facet screws, anterior plates or interbody cages). The ASPEN Spinous Process System can be used with or without bone graftingSystem can be used with or without bone grafting..


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Aspen Device Indications - EUAspen Device Indications - EU• The Aspen Spinous Process System is a spinous process fixation device intended to The Aspen Spinous Process System is a spinous process fixation device intended to

provide stabilization in the thoracic, lumbar and sacral spine (T1—S1). It can be provide stabilization in the thoracic, lumbar and sacral spine (T1—S1). It can be

used used as an adjunct to interbody and/or posterior fusion as an adjunct to interbody and/or posterior fusion or as a standalone fixation device. or as a standalone fixation device. The Aspen Spinous Process The Aspen Spinous Process System is indicated in the treatment of the following conditions:System is indicated in the treatment of the following conditions:• Degenerative disc diseaseDegenerative disc disease• Spinal stenosisSpinal stenosis• SpondylolisthesisSpondylolisthesis• Trauma (e.g. fractures, dislocation)Trauma (e.g. fractures, dislocation)• Spinal deformities (scoliosis, kyphosis, lordosis)Spinal deformities (scoliosis, kyphosis, lordosis)• Spinal tumorsSpinal tumors• Pseudoarthrosis or failed previous fusion surgeryPseudoarthrosis or failed previous fusion surgery• Spinal instabilitySpinal instability

• The Aspen Spinous Process System can be used in single- or multi-level constructs. The Aspen Spinous Process System can be used in single- or multi-level constructs. It can be used alone or in combination with other spinal devices (e.g. pedicle screws, It can be used alone or in combination with other spinal devices (e.g. pedicle screws, facet screws, anterior plates or interbody cages). The ASPEN Spinous Process facet screws, anterior plates or interbody cages). The ASPEN Spinous Process System can be used with or without bone graftingSystem can be used with or without bone grafting..


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• Open fenestrated bone graft Open fenestrated bone graft enclosure (central barrel)enclosure (central barrel)

• Facilitates placement of bone Facilitates placement of bone graftgraft

• Mitigates migration of posterior Mitigates migration of posterior bone graft materialbone graft material

• Ability to place bone graft inside Ability to place bone graft inside the barrel, anterior and the barrel, anterior and posterior to the barrelposterior to the barrel

• Central barrel supports Central barrel supports interbody and/or posterior interbody and/or posterior fusions by sharing compressive fusions by sharing compressive loadsloads

Integrated Bone Graft EnclosureIntegrated Bone Graft Enclosure


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Histopathological Preparation and Evaluation Histopathological Preparation and Evaluation of Sheep Lumbar Arthrodesisof Sheep Lumbar Arthrodesis66

Fusion permits long term maintainance of stability parameters as compared to ISA without fusion


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Radiographic fusionRadiographic fusion


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Aspen’s Clinical Applications in the U.S.Aspen’s Clinical Applications in the U.S.

POSTERIOR FUSION-No interbody-Alternative to decompression alone-Fills gap between decompression alone and pedicle screws

ASPEN + INTERBODY-TLIF, PLIF, ALIF, LLIF-Alternative to pedicle screws

OTHER

Tumor, trau

ma, etc.


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An Alternative to An Alternative to Pedicle Screws or Anterior PlatesPedicle Screws or Anterior Plates

• Minimally Invasive Fusion DeviceMinimally Invasive Fusion Device• Provides Efficient Placement for Secure FixationProvides Efficient Placement for Secure Fixation• Innovative Design Accommodates Wide Range of Innovative Design Accommodates Wide Range of

Anatomical VariationAnatomical Variation• Integrated Bone Graft EnclosureIntegrated Bone Graft Enclosure


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Case ExamplesCase Examples


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Combined with Screws for Additional RigidityCombined with Screws for Additional Rigidity

Facet Screws

Facet ScrewsUnilateral Pedicle

Screws

Unilateral Pedicle Screws

Supplemental fixation to augment lateral bending (ideal to support TLIF)


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Foramen Height


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Foramen Height


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Scientific DataScientific Data


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BiomechanicsBiomechanics


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Study RationaleStudy Rationale

To determine if the ISA in the setting of To determine if the ISA in the setting of ALIF and ALIF and TLIFTLIF provides adequate limitation in ROM as provides adequate limitation in ROM as compared to more conventional fixation compared to more conventional fixation techniquestechniques

To determine if the use of an ISA has any bearing To determine if the use of an ISA has any bearing on foraminal heighton foraminal height

To determine if the ISA leads to any significant To determine if the ISA leads to any significant changes in focal or regional sagittal balancechanges in focal or regional sagittal balance


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Study RationaleStudy Rationale

To determine if the ISA in the setting of To determine if the ISA in the setting of ALIF and ALIF and TLIFTLIF provides adequate limitation in ROM as provides adequate limitation in ROM as compared to more conventional fixation compared to more conventional fixation techniquestechniques

To determine if the use of an ISA has To determine if the use of an ISA has any bearing on foraminal heightany bearing on foraminal height

To determine if the ISA leads to any To determine if the ISA leads to any significant changes in focal or regional significant changes in focal or regional sagittal balancesagittal balance


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MethodsMethods 7 human specimen (L3-S1)7 human specimen (L3-S1) Instrumented at L4-L5Instrumented at L4-L5 3-D motion analysis using Optotrak IR system3-D motion analysis using Optotrak IR systemLoading apparatuses:Loading apparatuses:

Pure moment testing using MTSPure moment testing using MTSCompression flexion apparatusCompression flexion apparatus

Studied Studied Nondestructive flexibility (angular range of motion in Nondestructive flexibility (angular range of motion in

response to controlled load)response to controlled load)Foraminal height changeForaminal height changeChanges in sagittal balanceChanges in sagittal balance


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MethodsMethods

Pure moments (7.5 Nm Pure moments (7.5 Nm maximum) to induce:maximum) to induce:Flexion, extensionFlexion, extensionLeft and right lateral Left and right lateral

bendingbendingLeft and right axial Left and right axial

rotationrotation


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There was a greater and more consistent increase in foraminal height in conditions in which the ISA was used

The differences seen between groups were not statistically significant

There was a large degree of variability in height restoration achieved when ISA not used

Upright Foramen Height Change

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

ISA O

nly

ALIF+IS

A

ALIF+IS

A+Plate

ALIF+Plat

e

ALIF O

nly

ALIF+Bila

t PS

Hei

ght

Cha

nge

(mm

)

Foraminal Height


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Mean Upright Foramen Height Change

0

0.5

1

1.5

2

2.5

Bilat P

S (N=5)

ISA O

nly

TLIF+ IS

A

TLIF+IS

A+Unilat

PS

TLIF+ U

nilat

PS

TLIF+ B

ilat P

SHei

ght

Cha

nge

(mm

)

p>0.33

p>0.48


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FatigueFatigue

• Fatigue Protocol:Fatigue Protocol:– PS at L2-L3, ISA at L4-L5 (half of specimens)PS at L2-L3, ISA at L4-L5 (half of specimens)– ISA at L2-L3, PS at L4-L5 (half of specimens)ISA at L2-L3, PS at L4-L5 (half of specimens)– 500 cycles fatigue at 7.5 Nm pure moment applied in 500 cycles fatigue at 7.5 Nm pure moment applied in

flexion, extension, left lateral bending, right lateral flexion, extension, left lateral bending, right lateral bending, left axial rotation, right axial rotation bending, left axial rotation, right axial rotation (3000 cycles total)(3000 cycles total)

– Angular motion recorded at each cycleAngular motion recorded at each cycle– Peak load increased in 1.5 Nm increments and Peak load increased in 1.5 Nm increments and

cycling repeated until visible failure at one or both cycling repeated until visible failure at one or both levelslevels


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Foraminal HeightForaminal Height

The ISA limited changes in foraminal height with flexion/extension to a greater degree than other constructs


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Mean Angular Increase after Fatigue (N=6)

0

2

4

6

8

10

12

Flexion-Extension Axial Rotation Lateral Bending

Ang

le (

Deg

rees

)

Interspinous Anchor

Pedicle Screws-Rods

(no statistically significant differences; p>0.16)


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Sagittal BalanceSagittal Balance

ISA caused an increase in flexion at the index levelUnder load, there was compensatory extension at the adjacent levels


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Single Surgeon Single Surgeon Aspen Clinical ExperienceAspen Clinical Experience

-Preliminary Results--Preliminary Results-Courtesy of Dean Karaholios MDCourtesy of Dean Karaholios MD

• Overall experience >100 casesOverall experience >100 cases• 40 levels in 2008 (approximately 21 cases)40 levels in 2008 (approximately 21 cases)• 35 levels in 2009 (approximately 19 cases)35 levels in 2009 (approximately 19 cases)• 10 levels in 2010 through March10 levels in 2010 through March


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IndicationsIndications

• Backup ALIFBackup ALIF• Backup TLIFBackup TLIF• Decompression and FusionDecompression and Fusion

• Herniated discHerniated disc• Hemi laminectomyHemi laminectomy

• Decompression in ScoliosisDecompression in Scoliosis• Tumor ResectionTumor Resection• No stand-alone (without arthrodesis)No stand-alone (without arthrodesis)


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Clinical ResultsClinical Results

• N=50N=50• 38 patients improved (76%)38 patients improved (76%)• 8 patients without significant improvement (16%)8 patients without significant improvement (16%)• 4 patients with worse symptoms (8%)4 patients with worse symptoms (8%)• 1 reoperation for hematoma evacuation1 reoperation for hematoma evacuation• 2 reoperations for revision of construct2 reoperations for revision of construct• No new neurological deficitsNo new neurological deficits


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ConclusionsConclusionsForaminal height is increased and Foraminal height is increased and

maintained with ISAmaintained with ISA

ISA does not create a change in regional ISA does not create a change in regional sagittal balance under loadsagittal balance under load

Fatigue testing appears to show that ISA Fatigue testing appears to show that ISA constructs withstand repetitive cycling constructs withstand repetitive cycling better than constructs without ISAbetter than constructs without ISA


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ConclusionsConclusionsWith respect to immediate fixation rigidity, the With respect to immediate fixation rigidity, the

Aspen ISA appears to be a viable fixation solution Aspen ISA appears to be a viable fixation solution when used in conjunction with ALIF and/or TLIFwhen used in conjunction with ALIF and/or TLIF

Appears to better assure long standing Appears to better assure long standing maintenance of foraminal height along with fusionmaintenance of foraminal height along with fusion


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Thank YouThank You

Interspinous Vertebral Fixation with Fusion or with Distraction Alone:Reasons Why One is Better then the Other

Dicembre 7, Ore 13:20

Interspinous Fixation in the Stable Motion Segment

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