Upper Cervical Spine Loading Simulating a Dynamic Low-Speed Collision Significantly Increases the Risk of Pain Compared to Quasi-Static Loading With Equivalent Neck Kinematics

Vertebral Level-dependent Kinematics of Female and Male Necks Under G+x Loading

INTRODUCTION

Size-matched volunteer studies report gender-dependent variations in spine morphology, and head mass and inertia properties. The objective of this study was to determine the influence of these properties on upper and lower cervical spine temporal kinematics during G+x loading.

METHODS

Parametrized three-dimensional head-neck finite element models were used, and impacts were applied at 1.8 and 2.6 m/s at the distal end. Details are given in the article. Contributions of population-based variations in morphological and mass-related variables on temporal kinematics were evaluated using sensitivity analysis. Influence of variations on time to maximum nonphysiological curve formation, and flexion of upper and extension of the lower spines were analyzed for male-like and female-like spines.

RESULTS

Upper and lower spines responded with initial flexion and extension, resulting in a nonphysiological curve. Time to maximum nonphysiological curve and range of motions (ROMs) of the cervical column ranged from 45 to 66 ms, and 30 to 42 deg. Vertebral depth and location of the head center of gravity (cg) along anteroposterior axis were most influential variables for the upper spine flexion. Location of head cg along anteroposterior axis had the greatest influence on the time of the curve. Both anteroposterior and vertical locations of head cg, disc height, vertebral depth, head mass, and size were influential for the lower spine extension kinematics.

CONCLUSIONS

Models with lesser vertebral depth, that is, female-like spines, experienced greater range of motions and pronounced nonphysiological curves. This results in greater distraction/stretch of the posterior upper spine complex, a phenomenon attributed to suboccipital headaches. Forward location of head cg along anteroposterior axis had the greatest influence on upper and lower spine motions and time of formation of the curve. Any increased anteroposterior location of cg attributable to head supported mass may induce greater risk of injuries/neck pain in women during G+x loading.

Rear-Impact Neck Whiplash: Role of Head Inertial Properties and Spine Morphological Variations on Segmental Rotations

Whiplash injuries continue to be a concern in low-speed rear impact. This study was designed to investigate the role of variations in spine morphology and head inertia properties on cervical spine segmental rotation in rear-impact whiplash loading. Vertebral morphology is rarely considered as an input parameter in spine finite element (FE) models. A methodology toward considering morphological variations as input parameters and identifying the influential variations is presented in this paper. A cervical spine FE model, with its morphology parametrized using mesh morphing, was used to study the influence of disk height, anteroposterior vertebral depth, and segmental size, as well as variations in head mass, moment of inertia, and center of mass locations. The influence of these variations on the characteristic S-curve formation in whiplash response was evaluated using the peak C2–C3 flexion marking the maximum S-curve formation and time taken for the formation of maximum S-curve. The peak C2–C3 flexion in the S-curve formation was most influenced by disk height and vertebral depth, followed by anteroposterior head center of mass location. The time to maximum S-curve was most influenced by the anteroposterior location of head center of mass. The influence of gender-dependent variations, such as the vertebral depth, suggests that they contribute to the greater segmental rotations observed in females resulting in different S-curve formation from men. These results suggest that both spine morphology and head inertia properties should be considered to describe rear-impact responses.

The Interface of Mechanics and Nociception in Joint Pathophysiology: Insights From the Facet and Temporomandibular Joints

Chronic joint pain is a widespread problem that frequently occurs with aging and trauma. Pain occurs most often in synovial joints, the body's load bearing joints. The mechanical and molecular mechanisms contributing to synovial joint pain are reviewed using two examples, the cervical spinal facet joints and the temporomandibular joint (TMJ). Although much work has focused on the macroscale mechanics of joints in health and disease, the combined influence of tissue mechanics, molecular processes, and nociception in joint pain has only recently become a focus. Trauma and repeated loading can induce structural and biochemical changes in joints, altering their microenvironment and modifying the biomechanics of their constitutive tissues, which themselves are innervated. Peripheral pain sensors can become activated in response to changes in the joint microenvironment and relay pain signals to the spinal cord and brain where pain is processed and perceived. In some cases, pain circuitry is permanently changed, which may be a potential mechanism for sustained joint pain. However, it is most likely that alterations in both the joint microenvironment and the central nervous system (CNS) contribute to chronic pain. As such, the challenge of treating joint pain and degeneration is temporally and spatially complicated. This review summarizes anatomy, physiology, and pathophysiology of these joints and the sensory pain relays. Pain pathways are postulated to be sensitized by many factors, including degeneration and biochemical priming, with effects on thresholds for mechanical injury and/or dysfunction. Initiators of joint pain are discussed in the context of clinical challenges including the diagnosis and treatment of pain.