376 - Biomechanical Evaluation of the Multi-directional Flexibility Properti...

#376 Biomechanical Evaluation of the Multi-directional Flexibility Properties of an Interbody Cage with Three Integrated Cancellous Lag Screws in Two-level Cervical Spine Fusion Constructs

Basic Sciences-Research

Poster Presented by: A. Castellvi

Author(s):

B.G. Santoni (1)
A. Nayak (1)
C.R. James (1)
A. Kannan (2)
A. Cabezas (1)
M. Adu-Lartey (3)
A.E. Castellvi (3)

(1) Foundation for Orthopaedic Research and Education, Orthopaedic Biomechanics Research, Tampa, FL, USA
(2) University of South Florida, Medicine, Tampa, FL, USA
(3) Florida Orthopaedic Institute, Center for Spinal Surgery and Disorders, Tampa, FL, USA

Abstract

Study Purpose: Despite an increase in clinical use of no-profile integrated interbody cages for ACDF, little biomechanical data exists describing their stabilizing effect relative to traditional anterior plating. The purpose of this study was to quantify the stabilizing effect of the an integrated interbody fusion device with three cancellous lag screws at the C4-C5 and C5-C6 levels and compare the relative reduction in ROM at these levels to standard anterior rigid plate and screws used in ACDF.

Materials and Methods: Seven (n=7) cervical spines (C3-C7) were dissected from fresh-frozen, human cadaveric specimens and subjected to pure-moment loading (± 1.5 N-m) in flexion-extension, lateral bending and axial rotation. No compressive follower load was used. The specimens were tested in the following order:

(1) Intact;

(2) following discectomy, decompression and insertion of the integrated interbody device (IIB) at the C4-C5 and C5-C6 levels;

(3) following removal of the integrated screws and placement of an anterior locking plate (ALP) at C4-C5 and C5-C6; and

(4) in a cage only (CO) configuration with screws and anterior plate removed. Intervertebral ROM was obtained opto-electronically and compared across groups.

Results: Combined ROM reductions over the C4-C5 and C5-C6 levels were compared in all three motion planes.

Flexion-extension, lateral bending and axial rotation ROM were significantly reduced over both levels by IIB and ALP instrumentation (p< 0.001) relative to the intact condition. Combined flexion-extension motion over the two contiguous instrumented levels was reduced by the rigid anterior plate (6.8 ± 3.7°) relative to the integrated interbody spacer (10.2 ± 4.6°) (p=0.041). There were no significant differences in ROM reductions over the two levels between the IIB and ALP groups in lateral bending or axial rotation (p>0.826). Over both levels, significant increases in flexion-extension (p=0.001), lateral bending (p=0.023) and axial rotation (p=0.001) ROM afforded by the CO condition relative to IIB instrumentation were noted.

Conclusion: In two-level cervical spine fusion constructs, fixation with an integrated interbody with three points of screw fixation affords similar reductions in lateral bending and axial rotation ROM relative to rigid anterior plating. While we identified a small, but statistically significant, reduction in sagittal plane range of motion conferred by the ALP relative to the integrated interbody spacers, the clinical significance of this finding over two contiguous levels may not be appreciable. Our kinematic findings may support clinical use of no-profile integrated interbody devices over two-contiguous levels in ACDF.

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