Moment-Rotation Behavior of Intervertebral Joints in Flexion-Extension, Lateral Bending, and Axial Rotation at All Levels of the Human Spine: A Structured Review and Meta-Regression Analysis

Spinal intervertebral joints are complex structures allowing motion in multiple directions, and manyexperimental studies have reported moment-rotation response. However, experimental methods,reporting of results, and levels of the spine tested vary widely, and a comprehensive assessment ofmoment-rotation response across all levels of the spine is lacking. This review aims to characterizemoment-rotation response in a consistent manner for all levels of the human spine. A literature searchwas conducted in PubMed for moment versus rotation data from mechanical testing of intact humancadaveric intervertebral joint specimens in flexion-extension, lateral bending, and axial rotation. A total of 45 studies were included, providing data from testing of an estimated 1,648 intervertebral joints from518 human cadavers. We used mixed-effects regression analysis to create 75 regression models of moment-rotation response (25 intervertebral joints3 directions). We found that a cubic polynomialmodel provides a good representation of the moment-rotation behavior of most intervertebral joints,and that compressive loading increases rotational stiffness throughout the spine in all directions. Theresults allow for the direct evaluation of intervertebral ranges of motion across the whole of the spinefor given loading conditions. The random-effects outcomes, representing standard deviations of themodel coefficients across the dataset, can aid understanding of normal variations in moment-rotationresponses. Overall these results fill a large gap, providing the first realistic and comprehensive represen-tations of moment-rotation behavior at all levels of the spine, with broad implications for surgicalplanning, medical device design, computational modeling, and understanding of spine biomechanics.