Vertebrectomy Model for the Mechanical Assessment of Fusionless Scoliosis Growth Rods

Abstract

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.