Transcript Comparison of Pedicle Screw Spinal Fixation for Fractures

Bridge vs. Tension Band Construct for
Spinal Fractures Fixation:
A Biomechanical Analysis
C. Richards, J. Ouellet, M. Fouse, N. Noiseux, P. Jarzem,
R. Reindl, D. Giannitsios, T. Steffan
ORTHOPAEDIC RESEARCH LABORATORY
Division of Orthopaedic Surgery, McGill University
Problem

Traditional pedicle screw
instrumentation:

Parallel to endplate

Kyphotic collapse is a
known complication

Risk of posterior pullout if
not supported anteriorly
Hypothesis
For spinal fracture fixation

bridge-type fixation = divergent screws
vs.
tension-band = parallel screws



Significantly stiffer

Better resistance to failure in kyphosis

Better resistance to screw pull-out
Hypothesis
>
Hypothesis
>
Purpose
Bridge vs. Tension Band Constructs


Construct stiffness
Ultimate failure load
800
Ultimate
Failure Load
700
600
Load (N)

500
400
Stiffness
300
200
100
0
0
20
40
Displacem ent (m m )
60
Materials and Methods
1.
Finite Element
Analysis of ASTM
Polyethylene
Constructs
Methods and Materials
1.
2.
Finite Element
Analysis of ASTM
Polyethylene
Constructs
Mechanical testing of
ASTM Polyethylene
Construct
Methods and Materials
1.
2.
3.
Finite Element
Analysis of ASTM
Polyethylene
Constructs
Mechanical testing of
ASTM Polyethylene
Construct
Mechanical testing of
Cadaveric Constructs
ASTM Corpectomy Model



UHMWPE blocks
Worst case scenario
for vertebral body
fracture
Followed precisely for
T-B Constructs

Pedicle screws inserted
parallel to horizontal
plane
ASTM Corpectomy Model

Altered for Bridge
Constructs

Change in pedicle screw
orientation w.r.t.
horizontal plane


16.5º superiorly
26.4º inferiorly
Finite Element Analysis

Linear FEA


3-D models of
ASTM constructs
Mechanical
properties of
polyethylene and
titanium
Finite Element Analysis


Models loaded at
100N, 300N, &
600N
Displacement
data generated
for each load
Polyethylene Construct

6 constructs built




3 TB
3 Bridge
Constructs loaded
using MTS
Load and displacement
data generated
Cadaveric Constructs

6 male cadavers
dissected


3 Matched pairs based
on Vertebral body size
and BMD
instrumented @ T11-L1


3 – TB Construct
3 – Bridge Construct
#2 Osteotome
Cadaveric Constructs

Potted in PMMA


Anterosuperior endplate
of superior vertebra free
Anteroinferior endplate
of inferior vertebra free
Cadaveric Constructs


Loaded using MTS
Load and
displacement data
generated
Results – Stiffness (N/mm)
40
34.1
35
Stiffness (N/mm)
p=0.015
p=0.012
30
25
21.6
20
17.3
20.6
15.2
18.4
15
10
5
0
FEA
Polyethylene
Cadavers
Results – Ultimate Failure Load
700
p=0.076
Ultimate Failure Load (N)
600
500
419
400
300
200
100
0
622
Results

All specimens were
evaluated for accuracy
and safety of schanz
screw insertion


Maximum angles as
determined by the
anatomic study were
achieved
No breech of pedicle wall
Results

Pattern of Failure

Tension Band Construct


All 3 constructs failed
into kyphosis
Screw pullout at the
pedicle-body junction
Results
Pattern of Failure


Bridge Construct

2/3 constructs failed
1.
2.
Screw pullout at the
pedicle-body junction
Screw pullout through
superior endplate
Discussion

Increased stiffness

Better protection of
anterior column


Allows better potential
for healing
Decrease risk of
kyphotic failure
Conclusions



Bridge Construct is significantly stiffer than the
Tension Band Construct
Ultimate failure load was 50% greater for the Bridge
Construct
Further Cadaveric testing is required and is ongoing
>
Thank You
C. Richards, J. Ouellet, M. Fouse, N. Noiseux, P. Jarzem,
R. Reindl, D. Giannitsios, T. Steffan
ORTHOPAEDIC RESEARCH LABORATORY
Division of Orthopaedic Surgery, McGill University