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Current neck injury criteria are based on structural failure of the spinal (vertebral) column without consideration of injury to the spinal cord. Since one of the primary functions of the vertebral column is to protect the cord, it stands to reason that a more refined measure of neck injury threshold would be the onset of spinal cord injury (SCI). This study investigated the relationship between axial strains in the cervical vertebral column and the spinal cord using an in vitro primate model (n=10) under continuous tensile loading. Mean failure loads occurred at 1951.5±396N with failure strains in the vertebral column of 16±5% at the level of failure. Average tensile strains in the spinal cord at failure were 11±5% resulting in a mean coupling ratio of 0.54±0.17 between C1 and C7. The level of peak strain measured in the spinal cord did not always occur at the location of vertebral column failure. Spinal cord strains were less than spine strains and coupling ratios were not significantly different along the length of the spine. The largest coupling ratio was measured in the atlanto-occipital joint whereas the smallest coupling ratio occurred at the adjacent C1-C2 joint. Language: en

To prevent spinal cord injury, optimize treatments for it, and better understand spinal cord pathologies such as spondylotic myelopathy, the interaction between the spinal column and the spinal cord during injury and pathology must be understood. The spinal cord is a complex and very soft tissue that changes properties rapidly after death and is difficult to model. Our objective was to develop a physical surrogate spinal cord with material properties closely corresponding to the in vivo human spinal cord that would be suitable for studying spinal cord injury under a variety of injurious conditions. Appropriate target material properties were identified from published studies and several candidate surrogate materials were screened, under uniaxial tension, in a materials testing machine. QM Skin 30, a silicone elastomer, was identified as the most appropriate material. Spinal cords manufactured from QM Skin 30 were tested under uniaxial tension and transverse compression. Rectangular specimens of QM Skin 30 were also tested under uniform compression. QM Skin 30 produced surrogate cords with a Young's modulus in tension and compression approximately matching values reported for in vivo animal spinal cords (0.25 and 0.20 MPa, respectively). The tensile and compressive Young's modulus and the behavior of the surrogate cord simulated the nonlinear behavior of the in vivo spinal cord.

A biomechanical study using ex vivo bovine spinal cord and dura, and a synthetic surrogate spinal cord with bovine dura.To investigate the effect of cerebrospinal fluid (CSF) on spinal cord deformation characteristics and to evaluate the biofidelity of a new surrogate spinal cord using an ex vivo bovine model of the burst fracture process.Spinal cord injury is associated with significant personal, economic and social costs. The role of CSF during the injury event and its effect on the spinal cord deformation and neurologic injury is not well understood. Such knowledge could inform preventative strategies and clinical interventions and aid the development and validation of experimental and computational models.The transverse impact of a propelled bone fragment analogue with bovine and surrogate cord models was recorded with high speed video and the images analyzed to determine deformation trajectories. Each cord specimen was tested in 3 states: with dura and CSF, with dura only, and without dura. The effect of these states on deformation magnitude, duration, and energy loss parameters was assessed. RESULTS.: The estimated spinal cord deformation was significantly reduced, although not eliminated, in the presence of CSF when compared to the bare state. The duration of deformation was generally increased in the presence of CSF, though this difference was not statistically significant. This may indicate a reduction in the cord-fragment interaction force for a given impulse. The dura was found to have no significant effect on deformation parameters for the bovine spinal cord. The deformation of the surrogate cord gave similar trends for the different states in comparison to the bovine cord, but was significantly less than the bovine spinal cord for all conditions.The results indicate that the protective mechanism of CSF may not eliminate cord deformationunder the high energy transverse impact characteristic of a burst fracture. However, CSF may contribute to a lessening of cord deformation and applied force.

This chapter deals with the musculature actuation and biomechanics of the spine. Muscle contraction is initiated by impulse from motor neurons. A neuron can branch into many axons, each ending on a muscle fiber. Regulation of muscle force is controlled by the size and number of motor units recruited and by the frequency of the applied nerve impulse. This chapter illustrates that muscle forces occur in two forms: active and passive force. The active and passive muscle forces work together to produce the total force in the muscle. A single muscle fiber generates its greatest active force at resting length when the passive force component is negligible. Moreover, the loads on the spine are also affected by the weight of the body segments being supported above the spinal level being considered. The techniques used to address the question of spine loading have included purely theoretical mathematical models combines mathematical models and experimental data and purely experimental approaches.