Biomechanical Aspects of Spinal Cord Injury

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Biomechanical Aspects of Spinal Cord Injury

• Thomas R. Oxland PhD PEng
• Professor Director
• Division of Orthopaedic Engineering Research
• Departments of Orthopaedics Mechanical
  Engineering
• The University of British Columbia
• Vancouver Coastal Health Research Institute

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UBC The University of British Columbia

• 40,000 students
• 4,000 faculty

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UBC Department of Orthopaedics

• 65 faculty members
• 5 teaching hospitals
• basic clinical research

• seven Divisions
• Athletic Injuries
• Lower Limb Reconstruction
• Upper Limb Reconstruction
• Pediatrics
• Spine
• Trauma
• Orthopaedic Engineering Research

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Orthopaedic Engineering Research (DOER)

• the application of engineering principles to
  clinically relevant problems in the field of
  Orthopaedics

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DOER at UBC

• Clive Duncan
• Bassam Masri
• Don Garbuz
• Marcel Dvorak
• Brian Kwon
• Charles Fisher
• Pierre Guy
• Peter OBrien
• Robert McCormack
• Bill Regan

• Thomas Oxland
• David Wilson
• Heather McKay
• Karim Khan
• Peter Cripton
• Steve Robinovitch
• Rizhi Wang
• Goran Fernlund
• Gail Thornton

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Research Themes

• Mechanisms of Spine and Spinal Cord Injury
  Oxland, Cripton, Kwon, Dvorak,Tetzlaff
• Etiology of Osteoarthritis Wilson, MacKay,
  Cibere
• Hip Fracture Prevention McKay, Khan,
  Robinovitch, Guy
• Surgical Solutions in presence of Bone Loss
• osteoporotic spine Oxland, Cripton, Dvorak,
  Fisher
• revision hip Oxland, Duncan, Masri, Fernlund

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SCI Epidemiology

• 11,000 new injuries/year in North America
  (40/million)
• 200,000 chronic injuries
• Average age 32
• 9.73 billion/year
• hospitalization, rehabilitation, medication,
  equipment, loss productivity

-Spinal Cord Injury Information Network -
www.spinalcord.uab.edu
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ICORD new home for Spinal Research Centre in
Vancouver

• Vancouver General Hospital
• 51 principal investigators
• 120,000 square feet
• Spinal clinics
• Rehabilitation research
• Molecular Biology
• Bioengineering
• Neuropysiology

February 2008
October 2008
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Theme 3- Develop novel animal models of SCI
where damage can be induced within an enclosed
vertebral column, thereby more accurately
mimicking human SCI. Can only be achieved
through the combined efforts of spine surgeons,
biomechanical engineers and neuroscientists
working side-by-side.
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Theme 3 - Overview
Spinal cord injury represents a mechanical insult
that triggers a biological response which results
in a wide range of clinical sequelae.
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Type of Vertebral Injury
40 Fracture Dislocation
Burst Fracture 30
SCIWORET 10
5 Dislocation
SCIWORA 5
10 Minor Fracture
Sekhon Fehlings Spine 2001
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Spinal Injury
BURST FRACTURE
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Clinical Observation

• the mechanism of column damage correlates with
  the neurological deficit
• Marar 1974, Tator 1983

. but current treatments do not incorporate
injury mechanism!
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Methods Cord/Column

• Surrogate Cord
• Silicone gel
• In vivo-like in tension
• Barium Sulfate added
• Oval shaped

Saari MASc 2006
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Methods Specimen Preparation

• Human cervical spines occiput to T2 (n 6)
• Surrogate head attached to occiput

Saari MASc 2006
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Methods Imaging

• High Speed X-ray
• Industrial X-ray source
• 75kV, 5mA
• 9 image intensifier
• Internal high speed camera
• 1000 frames per second
• 256 x 240 pixels

Image Intensifier
X-ray Source
Saari MASc 2006
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Saari MASc 2006
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Effect of Constraint
Flexion-compression injury model
Zhu 2008
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Compression to the Specimen
Zhu 2008
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Flexion-Compression (constrained)
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Flexion-Compression (unconstrained)
Zhu 2008
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Spinal Canal Occlusion
T1
T2
T3
T4
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Canal Occlusion
Zhu 2008
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Column-Canal Relationships
constrained
unconstrained
Zhu 2008
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Dynamic Spinal Canal Occlusion

• Transient occlusion gtgt Post-impact
• Effect of Constraint i.e. Boundary Conditions

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Methods - Injury Simulation

• Axial head-to-ground impact
• Drop Tower
• Drop height 0.6m
• Speed at impact 3m/s
• Carriage mass 15kg

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Pro-Neck-TorTM
Standard Helmet
Dr. Peter Cripton
http//injury.mech.ubc.ca http//www.proneckto
r.com
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Proof of Concept Study Results

• Axial Force Escape-Angle Interaction

56 reduction
15º, Med Stiffness, Extension Escape, Vimpact
3.2 m/s
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C4
C5
C6
Greaves 2008
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Von Mises StrainCompression
dorsal
ventral
dorsal
ventral
Greaves 2008
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Von Mises StrainDistraction
dorsal
ventral
dorsal
ventral
Greaves 2008
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Von Mises StrainDislocation
dorsal
ventral
ventral
dorsal
Greaves 2008
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Different Cord Strain Patterns
Greaves Annals BME 2008
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Contusion
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Dislocation
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Dislocation FEM of rat c-spine
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Spinal Canal Occlusion Transducer
Segmental Voltage segmental resistance
constant current (resistance ? area)
Raynak 1998
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Theme 3 - Overview
Spinal cord injury represents a mechanical insult
that triggers a biological response which results
in a wide range of clinical sequelae.
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Spinal Injury
BURST FRACTURE
Do these well-known spinal column injury patterns
create different spinal cord injuries?
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Injury Models
1970
1990
1980
1911
2004
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Contusion Paradigm
central cavitation with peripheral rim of spare
white matter
Figure from McDonald Belegu. J Neurotrauma 2006
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Type of Vertebral Injury
40 Fracture Dislocation
Burst Fracture 30
SCIWORET 10
5 Dislocation
SCIWORA 5
10 Minor Fracture
Sekhon Fehlings Spine 2001
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Experimental Animal Model
Distraction
Compression/Contusion
Shear/Dislocation
Choo PhD 2006
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UBC SCI Test System
Actuator 12mm
LVDT (0.001mm)
accelerometer (50 500G)
Load Cell (22 225N)
Choo PhD 2006
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Contusion
force (N)
velocity (m/s)
displacement (mm)
Cord surface
Choo PhD 2006
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Dislocation
velocity (m/s)
force (N)
displacement (mm)
Choo PhD 2006
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Distraction
40
30
20
force (N)
velocity (m/s)
displacement (mm)
10
0
Choo PhD 2006
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Hemorrhage
Choo PhD 2006
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Anatomy
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Study 1 Primary Injury
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Membrane Integrity
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Membrane Integrity
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Membrane Damage
Neuronal Cell Bodies
Axons
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Primary Injury

• 275-325g Sprague-Dawley rats
• Infused 0.375mg 10kD fluorescein dextran into
  cisterna magna
• Incubated for 1 hour 30 min surgery
• Injury 100cm/s _at_ C4/5
• 5 min sacrifice primary damage

Mechanism N Severity
Contusion 9 1.1mm
Dislocation 9 2.5mm
Distraction 9 4.1mm
Shams 8 -
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Estimating Severity
2.5mm
4.1mm
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Membrane DamageNeuronal Cell Bodies
Lesion
Rostral
Injury
Choo J. Neurosurg. 2007
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Membrane DamageAxons
Lesion
Rostral
Injury
Choo J. Neurosurg. 2007
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Rostro-Caudal Distribution
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Study 2 Early Secondary Injury
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Early Secondary Injury

• 275-325g Sprague-Dawley rats
• Infused 0.375mg 10kD fluorescein dextran into
  cisterna magna
• Incubated for 1 hour 30 min surgery
• Injury _at_ 100cm/s
• 0.75mg 10kD cascade-blue dextran _at_ 2hrs
• detect persistent membrane permeability
• 3hrs sacrifice early secondary

Mechanism N Severity
Contusion 10 1.1mm
Dislocation 10 2.5mm
Distraction 10 4.1mm
Shams 7 -
Dextran Controls 3 -
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Membrane Integrity at 3hrs
Pre-injury Dextran
Post-injury Dextran
Merged Image
Choo Exp. Neurol. 2008
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Secondary Axonal Injury
(ßAPP)
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Secondary Axonal Injury
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Secondary Axonal Injury
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Microglial Activation
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Microglial Activation
Choo Exp. Neurol. 2008
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Neurofilament
Choo Exp. Neurol. 2008
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Overall Patterns of Tissue Damage
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Tissue Damage Mechanics?
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Limitations

• Early time-points for analysis
• Comparable severities?
• Behaviorial differences?
• No therapies tested

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Injury Velocity
1 Wilcox, Boerger et al, J Biomech 2002 35(3)
381-384 2 Elert, The Physics Fact Book 2003
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Engineering Perspective
Bilston LE, Thibault, LE Ann Biomed Eng 1996
24(1) 67-74
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Results Hemorrhage
Control
Slow
Fast
Sparrey MASc 2004
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Results - Hemorrhage
Sparrey Spine in press
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Residual Compression

• Maintained compression following initial
  contusion injury
• Alleviate with decompression
• Burst fractures (30)
• Fracture dislocations (40)
• Residual cord compression
• lt Transient contusion

Compression
Decompressed
(Sekhon Fehlins 2001 Basso et al. 1996)
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Methodology Experimental

• Stabilize in test frame
• Lower actuator LD probe
• Inject CSF
• Activate heating coils
• LD baseline measurement
• Spinal cord injury
• Contusion
• Contusion 90 compression
• Contusion 40 compression

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Results Contusion Injury Parameters

• Contusion

• 40 RC

• 90 RC

Group Peak Displacement (mm) Peak Force (N) Peak Velocity (mm/s)
Contusion -1.01 (0.004) -1.59 (0.26) -708.3 (6.3)
40 Residual -1.01 (0.005) -1.60 (0.22) -708.3 (7.7)
90 Residual -1.03 (0.002) -1.41 (0.19) -711.9 (8.13)
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Results Load Relaxation Time

• Median time - 75, 50, 40, 30, 20, 10 and 5
  of peak force

• 90 RC slower than 40 RC or contusion
• lt 5 of peak contusion force within 11.8 sec

Sjovold MASc 2006
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Results Laser Doppler

• Analyzed 2, 30, 58, 62 and 90 minutes

Sjovold MASc 2006
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Results Gray Matter
Sjovold MASc 2006
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Summary

• SCI is a high-speed event that we are
  characterizing from a biomechanical perspective
• Cadaver models
• Mathematical models
• Small animal models
• Ultimate goal is a clinically relevant
  sub-classification of SCI

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Next Steps..

• Further characterize primary injury secondary
  changes
• Assess behavioural differences between
  mechanisms
• Determine the effectiveness of imaging (MRI) in
  differentiating between injury mechanisms
• Evaluate the efficacy of novel therapeutic
  strategies for spinal cord injury (e.g.
  neuroprotective, remyelination)

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Collaborators

• Anthony Choo
• Carolyn Sparrey
• Carolyn Greaves
• Simon Sjovold
• Liz Clarke (AUS)
• Amy Saari (PC)
• Shannon Reed (PC)
• Tim Bhatnagar
• Colin Russell

• Wolfram Tetzlaff
• Peter Cripton
• Marcel Dvorak
• Brian Kwon
• Charles Fisher
• Mohamed Gadala
• Piotr Kozlowski
• Lynne Bilston (AUS)

• Qingan Zhu
• Jie Liu
• Clarrie Lam
• Chad Larson
• Darrell Goertzen
• Andrew Yung

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ICORD new home for Spinal Research Centre in
Vancouver

• Vancouver General Hospital
• 51 principal investigators
• 120,000 square feet
• Spinal clinics
• Rehabilitation research
• Molecular Biology
• Bioengineering
• Neuropysiology

February 2008
October 2008
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Acknowledgements
Canadian Institutes of Health Research

• Canada Research Chairs Program

Rick Hansen Man in Motion Fund

• George W. Bagby Research Fund
• BC Leading Edge Endowment Fund

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Professor Manohar Panjabi

• Yale University
• 1970-2006

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Professor Clive Duncan

• Chairman of Orthopaedics at UBC from 1996-2006

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Thank you!
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THANK YOU!!