Pure Moment Testing for Spinal Biomechanics Applications: Fixed Versus 3D Floating Ring Cable-Driven Test Designs

For spine biomechanical tests, the cable-driven system in particular has been widely used to apply pure bending moments. The advantages to pure moment testing lie in its consistency as an accepted standard protocol across previous literature and its ability to ensure uniform loading across all levels of the spinal column. Of the methods used for pure moment testing, cable-driven set-ups are popular due to their low requirements and simple design. Crawford et al [1] were the first to employ this method, but prior work by our group indicated a discrepancy between applied and intended moment for this system in flexion-extension only [2]. We hypothesize that this discrepancy can be observed in other bending modes and minimized with a second-generation floating ring design to eliminate off-axis loads.