Variation in axial force and Variation in axial force and distribution at the vertebra-graft distribution at the vertebra-graft interface resulting in increased interface resulting in increased
multilevel anterior cervical fusions multilevel anterior cervical fusions with semi-constrained plateswith semi-constrained plates
John Finkenberg MD, Laurie Sanders John Finkenberg MD, Laurie Sanders BS,MS, Scot Miller DO BS,MS, Scot Miller DO San Diego, CaliforniaSan Diego, California
2010 2010
Study DesignStudy Design
Biomechanical study demonstrating Biomechanical study demonstrating a variation in axial pressure when a variation in axial pressure when using constrained or semi-using constrained or semi-constrained platesconstrained plates
Prospective, multi-center, patient Prospective, multi-center, patient outcome and radiographic study outcome and radiographic study evaluating fusion, SF-36, ODI and evaluating fusion, SF-36, ODI and VAS.VAS.
METHODMETHOD Four anterior cervical plates:Four anterior cervical plates:
° Cyprus (fixed) constrained screwsCyprus (fixed) constrained screws° Cyprus (fixed) semi-constrained screwsCyprus (fixed) semi-constrained screws° VueLock (fixed) semi-constrained screwsVueLock (fixed) semi-constrained screws° C-Tek Slotted (dynamic) constrained screwsC-Tek Slotted (dynamic) constrained screws
Bone blocks polyurethane foam Bone blocks polyurethane foam ° 15 pcf / .24 gm/cc density pre-formed15 pcf / .24 gm/cc density pre-formed
PCF-15 intervertebral bone graftPCF-15 intervertebral bone graft DynaMight 8841 apparatus Ingstron force DynaMight 8841 apparatus Ingstron force
applicationapplication° 25 N – 150 N (loading posterior half of graft) 25 N – 150 N (loading posterior half of graft)
PressureX pressure sensitive paper PressureX pressure sensitive paper ° Ultralow 28-85 psiUltralow 28-85 psi
Data collection Topaq system software Data collection Topaq system software
COMPUTER EVALUATIONCOMPUTER EVALUATION
Topaq®
Pressure Statistics
Pressurex®
Paper Exposure
Topaq®
Pseudocolor Analysis
Topaq®
Pressure Histogram
Anterior graft
Posterior graft
50-N 100-N 150-N
Fixed/Constrained Screws
Anterior Cervical Plating System
Fixed/Semi-Constrained Screws
Anterior Cervical Plating System
Dynamic/Semi-Constrained Screws
Anterior Cervical Plating System
CONCLUSIONCONCLUSION
Fixed Anterior Cervical Plates with Constrained Screws Fixed Anterior Cervical Plates with Constrained Screws shift the intervertebral axial forces anteriorly toward the shift the intervertebral axial forces anteriorly toward the plate.plate.
Anterior Cervical Plates with Semi-Constrained screws Anterior Cervical Plates with Semi-Constrained screws shifted the axial forces more posteriorly but the majority of shifted the axial forces more posteriorly but the majority of the forces were still in the anterior half of the graft.the forces were still in the anterior half of the graft.
Dynamic cervical plates noted increased axial force over Dynamic cervical plates noted increased axial force over the posterior portion of the graft where the load was the posterior portion of the graft where the load was placed.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
40.2
19.1
0.05.0
10.015.020.025.030.035.040.045.0
ODI Score
Pre-Op
Post-Op
p<0.001
Visual Analog (VAS) Pain Scales
-3.8-3.3
-3
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
Neck Arm Shoulder
Mean Improvement from Pre-op
p<0.001
SF-36 Change from Pre-Op(+ = Improvement, - =Worsening)
17.1
41.9
27.8
-3.1
19.817.1 17.6
9.8
-10
0
10
20
30
40
50
PF* RP* BP* GH VT* SF* RE* MH*
Change from PreOp* = p<0.001
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.
DisclosuresDisclosures
Biomet (Consultant)Biomet (Consultant) K2M, Satori World Medical (Stocks)K2M, Satori World Medical (Stocks) Biomet (Royalties)Biomet (Royalties)