A New Device for Multi-Axial Tissue Testing: Application to Combined Bending and Shear Loading of the Spine

摘要

A multi-axial test device was designed to obtain the material properties of the lumbar spine in combined loading modes. The custom-designed tester consists of a rigid platen driven by three DC-powered geared motors. Two motors, each connected to parallel linear actuators control the angular displacement (for flexion and extension) and vertical motion (for tension and compression), while a third DC motor connected to a threaded rod was employed to control the horizontal displacement (for anterior and posterior shear) of the rigid platen. The testing machine is driven in displacement-control mode by a feedback system based on data from three rotary potentiometers. Six entire lumbar spine segments (T12-S1) were potted in aluminum cups with DynaCast and tested within failure limits to compression, tension, anterior shear, posterior shear, flexion, extension, anterior shear-flexion, posterior shear-extension and finally in combined anterior shear-flexion loading. The specimens were hydrated throughout the tests with 0.1% saline solution and positioned in their natural lordosis curvature. All data was processed as per SAE J211 convention. This unique multi-axis tester can be used for testing spines and other tissue in combined loading modes that are not common to commercially available material testing systems.