Browsing by Author "Meadows, Kyle D."
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Item Can axial loading restore in vivo disc geometry, opening pressure, and T2 relaxation time?(JOR Spine, 2024-04-25) Newman, Harrah R.; Moore, Axel C.; Meadows, Kyle D.; Hilliard, Rachel L.; Boyes, Madeline S.; Vresilovic, Edward J.; Schaer, Thomas P.; Elliott, Dawn M.Background Cadaveric intervertebral discs are often studied for a variety of research questions, and outcomes are interpreted in the in vivo context. Unfortunately, the cadaveric disc does not inherently represent the LIVE condition, such that the disc structure (geometry), composition (T2 relaxation time), and mechanical function (opening pressure, OP) measured in the cadaver do not necessarily represent the in vivo disc. Methods We conducted serial evaluations in the Yucatan minipig of disc geometry, T2 relaxation time, and OP to quantify the changes that occur with progressive dissection and used axial loading to restore the in vivo condition. Results We found no difference in any parameter from LIVE to TORSO; thus, within 2 h of sacrifice, the TORSO disc can represent the LIVE condition. With serial dissection and sample preparation the disc height increased (SEGMENT height 18% higher than TORSO), OP decreased (POTTED was 67% lower than TORSO), and T2 time was unchanged. With axial loading, an imposed stress of 0.20–0.33 MPa returned the disc to in vivo, LIVE disc geometry and OP, although T2 time was decreased. There was a linear correlation between applied stress and OP, and this was conserved across multiple studies and species. Conclusion To restore the LIVE disc state in human studies or other animal models, we recommend measuring the OP/stress relationship and using this relationship to select the applied stress necessary to recover the in vivo condition.Item MRI based non-invasive detection and monitoring of tissue mechanics and degenerative changes in the intervertebral disc and the meniscus(University of Delaware, 2023) Meadows, Kyle D.Degeneration and injury of fibrocartilages are often implicated in painful musculoskeletal conditions, which cause the most years lived with disability worldwide. Low back pain (LBP) and osteoarthritis (OA) rank 1st and 2nd among musculoskeletal conditions, based on global burden of disease data. Additionally, spine and knee surgeries are among the most common orthopedic procedures every year. Disc and meniscus injuries are linked to higher rates of LBP and OA, respectively, but questions remain regarding the direct cause of this correlation and quantitative measures are limited. Fibrocartilage degeneration is currently evaluated via structural assessment of magnetic resonance images (MRI), but many people with degenerative tissues do not have pain. It is hypothesized that pain may be more closely linked to tissue function as opposed to structural degeneration. Invasive assessment of disc function has shown better specificity for identification of pain causing discs, and LBP is often exacerbated or abated by different postural positions. Similarly, work in the knee has suggested that mechanics may be better at detecting painful joints than tissue structure. Ex vivo testing of cadaveric tissues informs us that degenerate or injured tissues have altered mechanics, likely leading to altered joint kinematics in vivo, but these explant studies do not match the in vivo boundary conditions. In vivo measurement of tissue function is still in development. Development of in vivo assessment of tissue function may provide better context as to why these injuries lead to pain and what therapies and repairs should be targeting to remedy the situation. ☐ The objective of this thesis was to develop and apply methods for non-invasive measurement of function and degeneration of the intervertebral disc and meniscus that could be used to inform and direct clinical decisions related to aging and injury. First, I identified appropriate sequence parameters to acquire MR data and applied curve fitting methods to accurately calculate disc T2 in the presence of image signal noise (Aim 1). I then developed methods and analyses to evaluate the mechanical function of the discs via non-invasive MRI in a young, asymptomatic cohort to establish baseline in vivo disc mechanics (Aim 2). Next, knee joint kinematics were assessed in intact joints, following root tear, and following suture repair at an acute time point under physiological loading using novel MRI methods (Aim 3). Finally, similar methods were applied to a porcine model of meniscus injury to appraise joint health and progression of degeneration following tear or repair in the short-term due to mechanical and biological interactions including endogenous remodeling and healing (Aim 4). In summary, this dissertation developed and utilized tools to evaluate in vivo mechanical function in the spine and knee in relation to structural degenerative changes. These tools may be used in the future to assess the progression of degeneration over time and to test the effectiveness of different repair and treatment strategies for disc and meniscus injury.Item MRI-based measurement of in vivo disc mechanics in a young population due to flexion, extension, and diurnal loading(JOR Spine, 2023-01-09) Meadows, Kyle D.; Peloquin, John M.; Newman, Harrah R.; Cauchy, Peter J. K.; Vresilovic, Edward J.; Elliott, Dawn M.Background: Intervertebral disc degeneration is often implicated in low back pain; however, discs with structural degeneration often do not cause pain. It may be that disc mechanics can provide better diagnosis and identification of the pain source. In cadaveric testing, the degenerated disc has altered mechanics, but in vivo, disc mechanics remain unknown. To measure in vivo disc mechanics, noninvasive methods must be developed to apply and measure physiological deformations. Aim: Thus, this study aimed to develop methods to measure disc mechanical function via noninvasive MRI during flexion and extension and after diurnal loading in a young population. This data will serve as baseline disc mechanics to later compare across ages and in patients. Materials & Methods: To accomplish this, subjects were imaged in the morning in a reference supine position, in flexion, in extension, and at the end of the day in a supine position. Disc deformations and vertebral motions were used to quantify disc axial strain, changes in wedge angle, and anterior–posterior (A-P) shear displacement. T2 weighted MRI was also used to evaluate disc degeneration via Pfirrmann grading and T2 time. All measures were then tested for effect of sex and disc level. Results: We found that flexion and extension caused level-dependent strains in the anterior and posterior of the disc, changes in wedge angle, and A-P shear displacements. Flexion had higher magnitude changes overall. Diurnal loading did not cause level-dependent strains but did cause small level-dependent changes in wedge angle and A-P shear displacements. Discussion: Correlations between disc degeneration and mechanics were largest in flexion, likely due to the smaller contribution of the facet joints in this condition. Conclusion: In summary, this study established methods to measure in vivo disc mechanical function via noninvasive MRI and established a baseline in a young population that may be compared to older subjects and clinical disorders in the future.