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)