1. John Finkenberg MD, Laurie Sanders BS,MS, Scot Miller DO
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

2. Study Design
Biomechanical study demonstrating a variation in axial pressure when using constrained or semi-constrained plates
Prospective, multi-center, patient outcome and radiographic study evaluating fusion, SF-36, ODI and VAS.

3. METHOD Four anterior cervical plates: Bone blocks polyurethane foam
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 psi
Data collection Topaq system software

4. COMPUTER EVALUATION Pseudocolor Analysis Paper Exposure
Topaq®
Pseudocolor Analysis
Pressurex®
Paper Exposure
Anterior
graft
Posterior
graft
Topaq®
Pressure Histogram
Topaq®
Pressure Statistics

5. 50-N 100-N 150-N Fixed/ Constrained Screws Fixed/
Anterior Cervical Plating System
Fixed/
Semi-Constrained Screws
Anterior Cervical Plating System
Dynamic/
Semi-Constrained Screws
Anterior Cervical Plating System

6. 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.

7. 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

8. Modified Oswestry (ODI) Score
p<0.001

9. Visual Analog (VAS) Pain Scales

10. SF-36 Change from Pre-Op (+ = Improvement, - =Worsening)

11. 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.

12. Disclosures Biomet (Consultant) K2M, Satori World Medical (Stocks)
Biomet (Royalties)