Transcript Osteoporotic Spine Fixation: A Biomechanical Investigation

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
UBC – The University of British
Columbia
• 40,000 students
• 4,000 faculty
UBC Department of
Orthopaedics
• 65 faculty members
• 5 teaching hospitals
• basic & clinical
research
• seven Divisions
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Athletic Injuries
Lower Limb Reconstruction
Upper Limb Reconstruction
Pediatrics
Spine
Trauma
Orthopaedic Engineering
Research
Orthopaedic Engineering
Research (DOER)
• the application of engineering
principles to clinically relevant
problems in the field of Orthopaedics
DOER at UBC
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Thomas Oxland
David Wilson
Heather McKay
Karim Khan
Peter Cripton
Steve Robinovitch
Rizhi Wang
Goran Fernlund
Gail Thornton
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Clive Duncan
Bassam Masri
Don Garbuz
Marcel Dvorak
Brian Kwon
Charles Fisher
Pierre Guy
Peter O’Brien
Robert McCormack
Bill Regan
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]
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
ICORD – new home for Spinal
Research Centre in Vancouver
•Vancouver General Hospital
•51 principal investigators
•120,000 square feet
•Spinal clinics
February 2008
•Rehabilitation research
•Molecular Biology
•Bioengineering
•Neuropysiology
October 2008
Theme 3Develop 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.
Theme 3 - Overview
Spinal cord injury represents a
mechanical insult that triggers a
biological response which results in a
wide range of clinical sequelae.
Type of Vertebral Injury
40% Fracture Dislocation
Burst Fracture 30%
SCIWORET 10%
SCIWORA 5%
5% Dislocation
10% Minor Fracture
Sekhon & Fehlings Spine 2001
Spinal Injury
FRACTURE
DISLOCATION
BURST FRACTURE
FLEXIONDISTRACTION
Clinical Observation
• the mechanism of column damage
correlates with the neurological deficit
– Marar 1974, Tator 1983
…. but current treatments do not incorporate injury mechanism!
Methods – Cord/Column
• Surrogate Cord
– Silicone gel
– In vivo-like in
tension
• Barium Sulfate added
• Oval shaped
Saari MASc 2006
Methods – Specimen
Preparation
• Human cervical spines
occiput to T2 (n = 6)
• Surrogate head
attached to occiput
Saari MASc 2006
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
Saari MASc 2006
Effect of
Constraint
Flexion-compression
injury model
Zhu 2008
Compression to the Specimen
Displacement
Displacement (mm )
0
0.5
0.7
0.9
1.1
1.3
1.5
-5
-10
-15
-20
35 msec
-25
Time (sec)
Zhu 2008
Flexion-Compression (constrained)
Flexion-Compression (unconstrained)
Zhu 2008
Canal Occlusion
Spinal canal area (mm^2)
200
unconstrained
190
constrained
180
170
160
150
140
130
0
10
20
30
40
50
60
compression (mm)
Zhu 2008
Column-Canal Relationships
constrained
unconstrained
Zhu 2008
Pro-Neck-TorTM
Standard Helmet
Dr. Peter Cripton
http://injury.mech.ubc.ca
http://www.pronecktor.com
Proof of Concept Study – Results:
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Axial Force Escape-Angle Interaction
56%
reduction
15º, Med Stiffness, Extension Escape, Vimpact ~3.2 m/s
C4
C5
C6
Greaves 2008
Von Mises Strain
Compression
0.00 0.04 0.07 0.11 0.15 0.18 0.22 0.26 0.29 0.33
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.37
dorsal
ventral
dorsal
ventral
Greaves 2008
Von Mises Strain
Distraction
0.00 0.01 0.03 0.04 0.05 0.07 0.08 0.10 0.11 0.12
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.37
dorsal
0.02 0.03 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
ventral
dorsal
ventral
Greaves 2008
Von Mises Strain
0.00 0.03 0.07 0.10 0.13 0.17 0.20 0.23 0.27 0.30
Dislocation
0.00 0.04 0.08 0.11 0.14 0.18 0.21 0.25 0.28 0.32
dorsal
ventral
ventral
dorsal
Greaves 2008
Different Cord
Strain Patterns
Greaves Annals BME 2008
Contusion
Theme 3 - Overview
Spinal cord injury represents a
mechanical insult that triggers a
biological response which results in a
wide range of clinical sequelae.
Spinal Injury
FRACTURE
DISLOCATION
FLEXIONDISTRACTION
BURST FRACTURE
Do these well-known spinal column injury patterns
create different spinal cord injuries?
Injury Models
Transection
Weight drop
-Allen
1911
g-cm
-Albin
1970
d, OSU
-Noyes
1980
m
F, IH
-Scheff
1990
2004
d
h
clip
-Tator
NYU
-Gruner
Lateral
Distraction
Dislocation
-Maiman
-Fiford
Contusion Paradigm
… central cavitation with peripheral rim of spare white matter …
Figure from McDonald & Belegu. J Neurotrauma 2006
Type of Vertebral Injury
40% Fracture Dislocation
Burst Fracture 30%
SCIWORET 10%
SCIWORA 5%
5% Dislocation
10% Minor Fracture
Sekhon & Fehlings Spine 2001
Experimental Animal Model
Compression/Contusion Shear/Dislocation
Distraction
Choo PhD 2006
UBC SCI Test System
Actuator
12mm
LVDT
(0.001mm)
accelerometer
(50 & 500G)
Load Cell
(22 & 225N)
Choo PhD 2006
Contusion
4
4
3
2
2
1
1
0
Cord surface
force (N)
displacement (mm)
velocity (m/s)
3
0
-1
-1
-2
5.005
5.01
5.015
time (s)
5.02
-2
Choo PhD 2006
Dislocation
3
30
2.5
20
1
15
0.5
10
displacement (mm)
velocity (m/s)
1.5
0
force (N)
25
2
5
-0.5
-5
-1
2.995
3
3.005
time (s)
3.01
3.015
-10
Choo PhD 2006
displacement (mm)
velocity (m/s)
20
10
force (N)
Distraction
40
30
0
Choo PhD 2006
Hemorrhage
Choo PhD 2006
Anatomy
&
Study 1: Primary Injury
Membrane Integrity
Membrane Integrity
Membrane Damage
Neuronal Cell Bodies
NeuN
Axons
Primary Injury
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275-325g Sprague-Dawley rats
Infused 0.375mg 10kD fluorescein dextran into cisterna magna
Incubated for 1 hour + 30 min surgery
Injury ~100cm/s @ 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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Membrane Damage
Neuronal Cell Bodies
Injury
Lesion
Rostral
Choo J. Neurosurg. 2007
Membrane Damage
Axons
Injury
Lesion
Rostral
Choo J. Neurosurg. 2007
Rostro-Caudal Distribution
Study 2: Early Secondary Injury
Early Secondary Injury
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275-325g Sprague-Dawley rats
Infused 0.375mg 10kD fluorescein dextran into cisterna magna
Incubated for 1 hour + 30 min surgery
Injury @ ~100cm/s
0.75mg 10kD cascade-blue dextran @ 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
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Dextran Controls
3
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Membrane Integrity at 3hrs
Pre-injury Dextran
Post-injury Dextran
Merged Image
Choo Exp. Neurol. 2008
Secondary Axonal Injury
(βAPP)
Secondary Axonal Injury
Secondary Axonal Injury
Microglial Activation
Activation
Activation
Microglial Activation
Choo Exp. Neurol. 2008
Overall Patterns of Tissue Damage
Tissue Damage ≈ Mechanics?
Limitations
• Early time-points for analysis
• Comparable severities?
• Behaviorial differences?
• No therapies tested
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 subclassification of SCI
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)
Collaborators
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Anthony Choo
Carolyn Sparrey
Carolyn Greaves
Simon Sjovold
Liz Clarke (AUS)
Amy Saari (PC)
Shannon Reed
(PC)
• Tim Bhatnagar
• Colin Russell
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Wolfram Tetzlaff
Peter Cripton
Marcel Dvorak
Brian Kwon
Charles Fisher
Mohamed Gadala
Piotr Kozlowski
Lynne Bilston
(AUS)
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Qingan Zhu
Jie Liu
Clarrie Lam
Chad Larson
Darrell
Goertzen
• Andrew Yung
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
Professor Manohar Panjabi
Yale University
1970-2006
Professor Clive Duncan
Chairman of Orthopaedics
at UBC from 1996-2006
Thank you!