Time Varying Modulators of Spine Injury Mechanics and Material Properties of Collagen and the Intervertebral Disc

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The prevalence of sedentary and light activity occupations has increased 100% over the past five decades. These prolonged common physical exposures have been linked to the reporting of low back pain. To give context for the impact of low back pain, it is one of the top three occupational lost time problems, affects approximately 80% of the population, and has the longest number of years lived with a disability. Exposure to sedentary tasks impacts the mechanical response of the lumbar spine, attributed to spine flexion straining posterior tissues in sitting and extension compressing the intervertebral disc and facet joints in standing. These postures directly impact pain sensitivity and lumbar spine stiffness. During chronic physical exposures, the intervertebral disc of the spine can become disrupted with the cartilaginous endplate identified as the structure where the cascade of mechanical failure is initiated in the majority of disc herniations. A solid understanding of the injury mechanisms associated with mechanical loading is crucial for injury prevention. The biological repair mechanisms in the intervertebral disc are slower than the injury process, in part due to the lack of blood supply to this structure. Accordingly, examination of the microstructural initiation of damage is critical to minimize risk of tissue injury and future progression to low back pain. The overall direction of my research program investigates time-varying lumbar spine changes in response to prolonged mechanical loading to understand how these changes impact injury initiation, progression, and nociception. The causes of injury initiation and progression of the intervertebral disc structure of the spine due to chronic exposure will be investigated. Studies examining the demands on the low back of individuals when performing sedentary tasks, representing sitting and standing office computer or light assembly work, will be combined with investigations at the tissue level. An assessment of time-dependent stiffness and loading variability responses of spinal tissues will determine the resulting damage potential. The proposed studies will directly assess, at a tissue level, if sedentary prolonged exposures create a microstructural damage pathway for lumbar spine injury that could explain the link between sedentary tasks and low back pain. The outcomes from this research will provide time-dependent material properties that are linked to the initiation of spine damage at a microstructural level. Ultimately, the linking of chronic exposure with potential injury initiation would be a powerful and novel fundamental contribution in developing methods to assess daily loading and set sedentary exposure standards to prevent injuries. This work will provide knowledge of the underlying healthy tissue response in the low back, laying a foundation to develop usage guidelines for occupational workstations involving sit and stand components.