Influence of Axial Load and a 45-Degree Flexion Head Position on Cervical Spinal Stiffness in Healthy Young Adults

Abstract

Background: Neck pain is a major cause of disability worldwide. Poor neck posture such as using a smartphone or work-related additional cervical axial load, such headgear of aviators, can cause neck pain. This study aimed at investigating the role of head posture or additional axial load on spinal stiffness, a proxy measure to assess cervical motor control.Methods: The posterior-to-anterior cervical spinal stiffness of 49 young healthy male military employees [mean (SD) age 20 ± 1 years] was measured in two head positions: neutral and 45-degree flexed head position and two loading conditions: with and without additional 3 kg axial load. Each test condition comprised three trials. Measurements were taken at three cervical locations, i.e., spinous processes C2 and C7 and mid-cervical (MC).Results: Cervical spinal stiffness measurements showed good reliability in all test conditions. There was a significant three-way interaction between location × head position × load [F(2, 576) = 9.305, p < 0.001]. Significant two-way interactions were found between measurement locations × loading [F(2, 576) = 15.688, p < 0.001] and measurement locations × head position [F(2, 576) = 9.263, p < 0.001]. There was no significant interaction between loading × head position [F(1, 576) = 0.692, p = 0.406]. Post hoc analysis showed reduction of stiffness in all three measurement locations in flexion position. There was a decrease in stiffness in C2 with loading, increase in stiffness in C7 and no change in MC.Discussion: A flexed head posture leading to decreased stiffness of the cervical spine might contribute to neck pain, especially if the posture is prolonged and static, such as is the case with smartphone users. Regarding the additional load, stiffness decreased high cervical and increased low cervical. There was no change mid cervical. The lower spinal stiffness at the high cervical spine might be caused by capsular ligament laxity due to the buckling effect. At the lower cervical spine, the buckling effect seems to be less dominant, because the proximity to the ribs and sternum provide additional stiffness.

Biomechanical analysis of cervical spine (C2–C7) at different flexed postures

“…8 It resembles a significant increase in the load on the C7, which further affects the shear forces and IVD pressure, leading to the laxity of the CL of the facet joint. 37,38 Also, higher flexion angles cause NMSD with postural stress and muscular imbalances, resulting in anatomical structure deformation and nerve compression. 39,40 The limitations of the study are the FEA model, generated through CT images, pertains to one patient.…”

Effect of trunk exercise upon lumbar IVD height and vertebral compliance when performed supine with 1 g at the CoM compared to upright in 1 g

“…The triggered impulse propagation properties reflect vertebral compliance [51] captured via dedicated software (PulStarFRAS, Sense Technology Inc., USA). Resultant vertebral compliance (C1 to L5) is reported to possess good-test-rest reliability even with trained novice examiners [50], with excellent reliability across the spine [52]. Assessment at each spinous process was performed twice and averaged [53].…”

“…However, the muscle volume pressure exerted on the vertebral column associated with our trunk muscle exercise is presumably low and broadly distributed [57]. Indeed, IVD compression has been shown to depend upon loading characteristics including direction, frequency magnitude and duration [21] with axial loading and exercise shown to provide compression forces that significantly differ between segments and vertebra [52].…”