The effect of axial compression and distraction on cervical facet mechanics during anterior shear, flexion, axial rotation, and lateral bending motions

Abstract

The subaxial cervical facets are important load-bearing structures, yet little is known about their mechanical response during physiological or traumatic intervertebral motion. Facet loading likely increases when intervertebral motions are superimposed with axial compression forces, increasing the risk of facet fracture. The aim of this study was to measure the mechanical response of the facets when intervertebral axial compression or distraction is superimposed on constrained, non-destructive shear, bending and rotation motions. Twelve C6/C7 motion segments (70±13 yr, nine male) were subjected to constrained quasi-static anterior shear (1 mm), axial rotation (4°), flexion (10°), and lateral bending (5°) motions. Each motion was superimposed with three axial conditions: 1) 50 N compression; 2) 300 N compression (simulating neck muscle contraction); and, 3) 2.5 mm distraction. Angular deflections, and principal and shear surface strains, of the bilateral C6 inferior facets were calculated from motion-capture data and rosette strain gauges, respectively. Linear mixed-effects models (α=0.05) assessed the effect of axial condition. Minimum principal and maximum shear strains were largest in the compressed condition for all motions except for maximum principal strains during axial rotation. For right axial rotation, maximum principal strains were larger for the contralateral facets, and minimum principal strains were larger for the left facets, regardless of axial condition. Sagittal deflections were largest in the compressed conditions during anterior shear and lateral bending motions, when adjusted for facet side.

Experimental analysis of the lower cervical spine in flexion with a focus on facet tracking

“…Facet sagittal rotations were consistent with the measured vertebral rotations, which was expected as computations consider vertebrae as rigid bodies. While the low posterior arch deflection appears to confirm this assumption, it contrasts with Quarrington et al [2019] reporting facet sagittal deflections of 0.25 ± 0.18° under 10° flexion with 50 N compression. However, on the one hand, they used marker carriers which could have amplified deflection measurements, and on the other hand this study used pins going through the spinous processes, which may have rigidified the vertebrae, explaining the low posterior arch deflection.…”

“…As such, it appears important to analyze lone FSUs without dynamic or muscular effects in order to assess the structural influence on facet kinematics. Furthermore, as dislocations are often associated with facet fractures [Foster et al, 2012], Quarrington et al [2018Quarrington et al [ , 2019 studied facet deflections and strains under low speed loading.…”

Ergonomic Comparison of Four Dental Workplace Concepts Using Inertial Motion Capture for Dentists and Dental Assistants

“…This working posture, especially the neck flexion, causes a 1.6-fold increase in cervical disc compression and a four-fold increase in anteroposterior shear at a posture of 45° compared to the neutral position [ 36 ]. Thus, these increases in cervical disc compression and shear forces during flexion, lateral flexion, and rotational movements must also be taken into account [ 37 , 38 ]. In the present analysis, the ERPs show that in the neck area, in all DWCs, between 55–59% of the working time was spent in the maximum possible RULA score.…”

Spine biomechanical testing methodologies: The controversy of consensus vs scientific evidence

“…Magnitude of applied moments ranges from 1.0 Nm 249,250 to 5.0 Nm 251 . Axial preloads typically range from 0 N (no axial load) to 125 N 156,181,257 and have been as high as 300 N 258 . ROM testing with a follower load of 100 N and applied moments in flex/extension of 2.0 Nm demonstrated highest fidelity and reproducibility relative to in vivo measurements 180,181 …”