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AbstractThe study aimed to investigate the dynamic characteristics of the cervical spine and determine the effect of the material properties of the cervical spinal components on it. A finite element model of the head-cervical spine was developed based on CT scan data, and the first six orders of modes (e.g. flexion-extension, lateral bending, and vertical, etc.) were verified by experimental and simulation studies. The material sensitivity study was conducted by varying elasticity modulus of cervical hard tissues (cortical bone, cancellous bone, endplates, and posterior elements) and soft tissues (intervertebral disc and ligaments). The results showed that increasing the elastic modulus of ligaments by 4 times increased the natural frequency by 77%, while increasing that of cancellous bone by 4 times only increased the natural frequency by 6%. In the axial mode, the cervical spine had not only axial deformation but also anterior-posterior deformation, with the largest deformation located at the intervertebral disc C6-C7. Decreasing the elastic modulus of a component in soft tissues by 80% increased modal displacement by up to 62%. The material properties of the intervertebral discs and ligaments had opposite effects on the modal displacement and deformation of the cervical spine. Low cervical discs were more susceptible to injury in a vertical vibration environment. Cervical spine dynamics were more sensitive to soft tissue material properties than to hard tissue material properties. Disc degeneration could reduce the range of vibratory motion of the cervical spine, thereby reducing the ability of the cervical spine to cushion head impacts. [ABSTRACT FROM AUTHOR]

Few studies investigate the impact of anterior-posterior excitation frequency on the time-domain vibrational response and injury risk of the lumbar spine in seated individuals. Firstly, this study utilised a previously developed finite element model of an upright seated human body on a rigid chair without a backrest to investigate the modes that affect the anterior-posterior vibrations of the seated body. Subsequently, transient dynamic analysis was employed to calculate the lumbar spine's time-domain responses (displacement, stress, and pressure) and risk factors under anteroposterior sinusoidal excitation at varying frequencies (1-8 Hz). Modal analysis suggested the frequencies significantly affecting the lumbar spine's vibration were notably at 4.7 Hz and 5.5 Hz. The transient analysis results and risk factor assessment indicated that the lumbar responses were most pronounced at 5 Hz. In addition, risk factor assessment showed that long-term exposure to 8 Hz vibration was associated with a greater risk of lumbar injury.