An alternative measurement tool for the identification of hysteretic responses in biological joints

In structural engineering, sophisticated multi-dimensional analysis techniques, such as the Restoring Force Method (RFM), have been established for complex, nonlinear hysteretic systems. The purpose of the present study was to apply the RFM to quantify nonlinear spine hysteresis responses under applied moments. First, synthetic hysteretic spine responses (n=50) were generated based on representative results from pure moment flexion-extension loading of a human cadaveric lumbar spine segment. Then, the RFM was applied to each hysteresis response to describe the flexion-extension rotation as a function of applied moment and simulated axial displacement using a set of 16 unique coefficients. Range of motion, neutral zone, elastic zone, and stiffness were also measured. The RFM coefficient corresponding to the 1st-order linear dependence of rotation on applied moment was dominant, and paralleled changes in elastic zone. The remaining RFM coefficients were not captured from the traditional biomechanical analysis. Therefore, the RFM may potentially supplement the traditional analysis to develop a more comprehensive, quantitative description of spine hysteresis. The results suggest the potential for more thorough and specific characterization of spine kinematics, and may lead to future applications of such techniques in characterizing biological structures.