Time-Varying Material Properties of the Intervertebral Disc and the Influence on Spine Joint Mechanics

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Low back pain affects approximately 80% of the population at some point in their life. The low back is the most frequently injured body area, has the highest average compensation costs, and results in more global disability than any other condition. Evidence suggests that the primary cause of low back pain is through mechanical exposure associated with everyday activities and industrial tasks. While tasks involving heavy lifting are often linked with low back pain, innocuous sedentary tasks such as prolonged standing or sitting have also been associated with low back pain. However, there is little understanding of how these sedentary, and seemingly benign tasks can result in injuries to the low back.****The overall direction of my research program is to investigate how time varying exposure to low level loading initiates and exacerbates altered joint mechanical performance lending insight to these low back injury pathways. The causes of injury initiation and progression in the structures of the healthy spine (e.g. the intervertebral disc) due to chronic exposure will be investigated. Mechanical injuries to the intervertebral disc are thought to be responsible for up to 50% of chronic low back pain cases. Studies examining the demands on the low back of healthy, injury free individuals when performing sedentary tasks representing sitting and standing office computer or light assembly work will be combined with investigations at the tissue level to assess time-dependent responses of spinal tissues and the resulting injury potential. A solid understanding of the joint performance and links to injury mechanisms associated with mechanical loading is critical for injury prevention, as 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. The ability of the spinal tissues to repair themselves can easily be outpaced by injury deterioration once the first stage of an injury to the intervertebral disc has occurred. ****The outcomes from this research will provide time-dependent tissue material properties that are currently unavailable and are a limiting factor in the understanding and modeling of the intervertebral disc and low back injuries. Ultimately, the linking of cumulative or chronic exposure with potential pain generation would be a powerful and novel fundamental contribution in developing methods to assess daily loading and set threshold limits or exposure standards to prevent injuries for sedentary tasks. 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 to stand components. **