Published: May 2012
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Fusionless scoliosis growth rod systems pose many challenges to benchtop biomechanical testing. This study was conducted in order to develop a vertebrectomy model capable of evaluating shear/corrective reduction forces, anterior/posterior load sharing, and long term fatigue properties of these systems. Portions of ASTM F1717 and ISO 12189 were used to develop a custom dynamic construct. Results from the corrective/shear reduction force test demonstrate an expected reduced shear/corrective force at the completion of fatigue testing. Additionally, a bimodal force– displacement curve was demonstrated during confined static compression testing, indicating an anterior/posterior load sharing function of the system. Fatigue testing of the dynamic construct demonstrated the potential to develop a fatigue curve and endurance limit of a growth rod system. Moreover, fatigue testing replicated common in vivo failures. The complexities of scoliosis treatment make the definition of a standardized construct difficult. However, application of the current model can serve as a tool to understand the basic mechanical interactions in these complex systems.
growth rods, biomechanical testing, scoliosis
Shorez, J. P.
Senior Research Engineer, Medtronic, Memphis, TN