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Stability and Load Sharing Characteristics of a Posterior Dynamic Stabilization Device

Daniel J. Cook, MS,1 Matthew S. Yeager, BS,1 Shankar S. Thampi, BS,2 Donald M. Whiting, MD,1,2 Boyle C. Cheng, PhD1,2

1Allegheny Health Network, Department of Neurosurgery, Pittsburgh, PA 2Drexel University College of Medicine, Pittsburgh, PA

Abstract

Background

Lumbar interbody fusion is a common treatment for a variety of spinal pathologies. It has been hypothesized that insufficient mechanical loading of the interbody graft can prevent proper fusion of the joint. The purpose of this study was to evaluate the mechanical stability and anterior column loading sharing characteristics of a posterior dynamic system compared to titanium rods in an anterior lumbar interbody fusion (ALIF) model.

Methods

Range of motion, interpedicular kinematics and interbody graft loading were measured in human cadaveric lumbar segments tested under a pure moment flexibility testing protocol.

Results

Both systems provided significant fixation compared to the intact condition and to an interbody spacer alone in flexion extension and lateral bending. No significant differences in fixation were detected between the devices. A significant decrease in graft loading was detected in flexion for the titanium rod treatment compared to spacer alone. No significant differences in graft loading were detected between the spacer alone and posterior dynamic system or between the posterior dynamic system and the titanium rod.

Conclusions

The results of this study indicate that the posterior dynamic system provides similar fixation compared to that of a titanium rod, however, studies designed to evaluate the efficacy of fixation in a cadaver model may not be sufficiently powered to establish differences in load sharing using the techniques described here.

keywords: 
Lumbar Spine Biomechanics, posterior dynamic stabilization, Load Sharing
Volume 9 Article 9
doi: 
10.14444/2009