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

Abstract

Spinal intervertebral joints are complex structures allowing motion in multiple directions, and many experimental studies have reported moment-rotation response. However, experimental methods, reporting of results, and levels of the spine tested vary widely, and a comprehensive assessment of moment-rotation response across all levels of the spine is lacking. This review aims to characterize moment-rotation response in a consistent manner for all levels of the human spine. A literature search was conducted in PubMed for moment versus rotation data from mechanical testing of intact human cadaveric 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 from 518 human cadavers. We used mixed-effects regression analysis to create 75 regression models of moment-rotation response (25 intervertebral joints × 3 directions). We found that a cubic polynomial model 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. The results allow for the direct evaluation of intervertebral ranges of motion across the whole of the spine for given loading conditions. The random-effects outcomes, representing standard deviations of the model coefficients across the dataset, can aid understanding of normal variations in moment-rotation responses. Overall these results fill a large gap, providing the first realistic and comprehensive representations of moment-rotation behavior at all levels of the spine, with broad implications for surgical planning, medical device design, computational modeling, and understanding of spine biomechanics.

Keywords: Cervical Spine; Follower load; Lumbar Spine; Mechanical Testing; Thoracic Spine.

Figure 1:

Example data (solid lines) from Mannen et al (2018) showing moment-rotation behavior of a single specimen at T8–9 in flexion (+) and extension (−) with 0, 200, and 400 N of compressive loading. Fitting Equation 4 to this data produces a prediction of moment as a function of rotation angle and compressive force (dashed lines), and fits the data very well (r² = 0.980).

Figure 2:

Example plot of regression results for FE at L4–5, showing non-linear behavior and effect of compressive load. The data are grouped based on compressive load applied (dots: F = 0 N; circles: 0 < F < 500 N; triangles: F > 500 N). Fixed effects regression equations are plotted for compressive loads of 0 N (solid line), 500 N (dashed line), and 1000 N (dotted line).

Figure 3:

Total ranges of motion (°) calculated from fixed-effect models for flexion-extension, lateral bending, and axial rotation, by level, with applied moments of ± 5 Nm and compressive loads of 0 and 500 N. The range of motion reported by White and Panjabi (1978) is shown for comparison.