Robotic Simulation of an Eccentric Lever Arm Protocol and a Novel Head Weight Protocol for Evaluation of the Subaxial Cervical Spine: An In Vitro Biomechancial Comparison

In vitro testing provides a critical tool for understanding the biomechanics of the subaxial cervical spine. Previous common testing protocols used to evaluate the subaxial cervical spine include pure moment, follower load, and eccentric lever arm (EL) loading methods [1,2,3]. Although these methods are widely accepted, there is always a goal to try to better simulate physiologic loading conditions. While the follower load attempts to simulate compression due to muscle activation, no previous protocol has taken into account the constant vertical force vector applied to C2 produced by the weight of the human head. Furthermore, we are unaware of previous direct protocol to protocol comparisons using the same testing platform and test specimens. Our multi-axis programmable robotic testing platform (Spine Robot) provides the means to explore such comparisons. The objectives of this study were: 1) to develop a novel head weight influenced loading protocol (HWL), 2) simulate and compare the EL protocol and the HWL protocol on a single programmable robotic testing frame with a consistent specimen sample group.