Variation in axial force and distribution at the vertebra-graft interface resulting in increased multilevel anterior cervical fusions with semi-constrained plates

1
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
• 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

4
COMPUTER EVALUATION
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 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
plt0.001
9
Visual Analog (VAS) Pain Scales
plt0.001
10
SF-36 Change from Pre-Op( Improvement, -
Worsening)
plt0.001
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)