Low back pain is responsible for approximately 90 billion dollars annual costs in the United States. Previous studies of disc structural integrity and mechanical function have identified key events in progressive disc degeneration including early loss of nucleus pulposus (NP) glycosaminoglycan content (which decreases NP pressure) progressing to annulus fibrosus (AF) radial and circumferential tears. While AF tears are thought to occur in response to alterations in the AF loading environment stemming from decreased NP pressure, the physical mechanisms for initiation and progression of AF tears are not understood. Very little is known about how the internal disc mechanics are affected by the state of degeneration or by physiological factors (e.g., diurnal hydration, loading rate). Moreover, local disc mechanics at the site of tears are completely unknown. We hypothesize that internal AF stresses and strains are elevated in response to reduced NP pressure and other degenerative changes affecting AF material properties, that local stress-strain concentrations occur adjacent to AF tears, and that dynamic loading further elevates the AF stress and strain. The objectives of this proposal are to quantify internal AF stress and strain and the effect of degenerative state (reduced NP pressure, AF tears), hydration, and dynamic loading on internal disc mechanics using an integrated experimental and modeling approach. Integration of experimental methods and models, which inform each other to address hypotheses for mechanical mechanisms of progressive disc degeneration, is a distinctive approach, and is our focus in the following 3 Specific Aims.
Aim 1 : Quantify the strain adjacent to AF tears under physiological loading of an intact bone-disc- bone unit. High-field microMRI, a custom built MR-compatible loading system, and state-of-the-art image registration will be applied to evaluate the role of degenerative state on AF stress-strain behavior and to specifically quantify strain fields around AF tears already present in the human cadaveric disc. Location, magnitude, and distribution of strains will be identified for each loading condition (compression, torsion, bending) at equilibrium.
Aim 2 : Develop a new disc FE model and validate it by comparing predicted and measured internal disc strains. The model will incorporate a hyperelastic biphasic constitutive material formulation that includes recently measured NP and AF tissue properties for fiber-reinforced anisotropy, nonlinearity, and osmotic swelling pressure.
Aim 3 : Calculate stresses and strains associated with degeneration, loading rate, hydration, and AF tears using the model from Aim 2. Incorporate degeneration by geometry and material properties and validate the effects of degeneration as done in Aim 2 for the non-degenerate disc. This work is significant in that it evaluates physical mechanisms in disc degeneration, a critical step in understanding and treating low back pain.
Lumbar disc degeneration and low back pain are both costly and devastating to the quality of life. Very little is known about how the internal disc mechanics are altered with degeneration and local mechanics at the site of tears are completely unknown. The objectives of this proposal are to quantify internal AF stress and strain and the effect of degenerative state, hydration, and dynamic loading using an integrated experimental and modeling approach. This work is significant in that it evaluates physical mechanisms in disc degeneration, a critical step in understanding and treating low back pain.
|Peloquin, John M; Yoder, Jonathon H; Jacobs, Nathan T et al. (2014) Human L3L4 intervertebral disc mean 3D shape, modes of variation, and their relationship to degeneration. J Biomech 47:2452-9|
|Cortes, Daniel H; Jacobs, Nathan T; DeLucca, John F et al. (2014) Elastic, permeability and swelling properties of human intervertebral disc tissues: A benchmark for tissue engineering. J Biomech 47:2088-94|
|Cortes, Daniel H; Elliott, Dawn M (2014) Accurate Prediction of Stress in Fibers with Distributed Orientations Using Generalized High-Order Structure Tensors. Mech Mater 75:73-83|
|Yoder, Jonathon H; Peloquin, John M; Song, Gang et al. (2014) Internal three-dimensional strains in human intervertebral discs under axial compression quantified noninvasively by magnetic resonance imaging and image registration. J Biomech Eng 136:|
|Showalter, Brent L; Malhotra, Neil R; Vresilovic, Edward J et al. (2014) Nucleotomy reduces the effects of cyclic compressive loading with unloaded recovery on human intervertebral discs. J Biomech 47:2633-40|
|Jacobs, Nathan T; Cortes, Daniel H; Peloquin, John M et al. (2014) Validation and application of an intervertebral disc finite element model utilizing independently constructed tissue-level constitutive formulations that are nonlinear, anisotropic, and time-dependent. J Biomech 47:2540-6|
|Jacobs, Nathan T; Cortes, Daniel H; Vresilovic, Edward J et al. (2013) Biaxial tension of fibrous tissue: using finite element methods to address experimental challenges arising from boundary conditions and anisotropy. J Biomech Eng 135:021004|
|Martin, John T; Gorth, Deborah J; Beattie, Elizabeth E et al. (2013) Needle puncture injury causes acute and long-term mechanical deficiency in a mouse model of intervertebral disc degeneration. J Orthop Res 31:1276-82|
|Moon, Sung M; Yoder, Jonathon H; Wright, Alexander C et al. (2013) Evaluation of intervertebral disc cartilaginous endplate structure using magnetic resonance imaging. Eur Spine J 22:1820-8|
|Showalter, Brent L; Beckstein, Jesse C; Martin, John T et al. (2012) Comparison of animal discs used in disc research to human lumbar disc: torsion mechanics and collagen content. Spine (Phila Pa 1976) 37:E900-7|
Showing the most recent 10 out of 26 publications