Variation in axial force and distribution at
the vertebra-graft interface resulting in
increased multilevel anterior cervical
fusions with semi-constrained plates
John Finkenberg MD, Laurie Sanders
BS,MS, Scot Miller DO
San Diego, California
2010
Study Design


Biomechanical study demonstrating a
variation in axial pressure when
using constrained or semiconstrained plates
Prospective, multi-center, patient
outcome and radiographic study
evaluating fusion, SF-36, ODI and
VAS.
METHOD

Four anterior cervical plates:
°
°
°
°

Cyprus (fixed) constrained screws
Cyprus (fixed) semi-constrained screws
VueLock (fixed) semi-constrained screws
C-Tek Slotted (dynamic) constrained screws
Bone blocks polyurethane foam
° 15 pcf / .24 gm/cc density pre-formed


PCF-15 intervertebral bone graft
DynaMight 8841 apparatus Ingstron force
application
° 25 N – 150 N (loading posterior half of graft)

PressureX pressure sensitive paper
° Ultralow 28-85 psi

Data collection Topaq system software
COMPUTER EVALUATION
Topaq®
Pressurex®
Pseudocolor Analysis
Paper Exposure
Anterior
graft
Posterior
graft
Topaq®
Pressure Statistics
Topaq®
Pressure Histogram
50-N
Fixed/
Constrained Screws
Anterior Cervical Plating System
Fixed/
Semi-Constrained Screws
Anterior Cervical Plating System
Dynamic/
Semi-Constrained Screws
Anterior Cervical Plating System
100-N
150-N
CONCLUSION



Fixed Anterior Cervical Plates with Constrained Screws
shift the intervertebral axial forces anteriorly toward the
plate.
Anterior Cervical Plates with Semi-Constrained screws
shifted the axial forces more posteriorly but the majority of
the forces were still in the anterior half of the graft.
Dynamic cervical plates noted increased axial force over
the posterior portion of the graft where the load was
placed.
Prospective Multicenter Study






186 Patients (72 men, 114 women)
78 one level, 87 two level and 21
three level
56 active smokers
102 workers compensation patients
131 allograft and 55 autograft
Two year follow-up
Modified Oswestry (ODI) Score
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
40.2
19.1
ODI Score
p<0.001
Pre-Op
Post-Op
Visual Analog (VAS) Pain Scales
0
-0.5
Neck
Arm
Shoulder
-1
-1.5
-2
-2.5
-3
-3.5
-4
-3.3
-3.8
Mean Improvement from Pre-op
p<0.001
-3
SF-36 Change from Pre-Op
(+ = Improvement, - =Worsening)
50
41.9
40
27.8
30
20
19.8
17.1
17.1
17.6
9.8
10
0
-3.1
-10
PF*
RP*
BP*
GH
VT*
Change from PreOp
* = p<0.001
SF*
RE*
MH*
Conclusion


96% fusion rate with no differences
noted for graft type, levels fused,
smoking history or workers
compensation coverage.
Increased axial forces over a larger
surface area promotes bone fusion at
the vertebra-graft interface.
Disclosures



Biomet (Consultant)
K2M, Satori World Medical (Stocks)
Biomet (Royalties)