Chronic low back pain affects an estimated 15–65% of the U.S. population. Disc degeneration is often accredited as the origin of low back pain. With degeneration comes the breakdown of proteoglycans, loss of water content, and a decrease in the height of the intervertebral disc (IVD). These changes likely affect the disc’s viscoelastic response, making modeling and subsequent prediction of degeneration mechanics difficult. Unfortunately, much of the previous mechanical testing of IVD tissues has involved excision of the tissue and disruption of annular fibers. To gain insight into the in situ viscoelastic material properties, we have developed a new methodology of hybrid confined / in situ compression. This technique also allows for the quantification of the residual stress and strain that the IVD experiences in vivo and improved viscoelastic modeling parameters. Residual measurements, to the knowledge of the authors, have yet to be reported in previous studies. Therefore, the purpose of this study was to define the viscoelastic properties of the intact intervertebral disc as well as the residual stress/strain specific to degeneration grade and location.

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