Effect of microgravity on mechanical loadings in lumbar spine at various postures: a numerical study.

The aim of this study was to quantitatively analyze the mechanical change of spinal segments (disc, muscle, and ligament) at various postures under microgravity using a full-body musculoskeletal modeling approach. Specifically, in the lumbar spine, the vertebra were modeled as rigid bodies, the intervertebral discs were modeled as 6-degree-of-freedom joints with linear force-deformation relationships, the disc swelling pressure was deformation dependent, the ligaments were modeled as piecewise linear elastic materials, the muscle strength was dependent on its functional cross-sectional area. The neutral posture and the "fetal tuck" posture in microgravity (short as "Neutral 0G" and "Fetal Tuck 0G", in our simulation, the G constant was set to 0 for simulating microgravity), and for comparison, the relaxed standing posture in 1G and 0G gravity (short as "Neutral 1G" and "Standing 0G") were simulated.

Effect of lumbar muscle atrophy on the mechanical loading change on lumbar intervertebral discs.

The objective of this study was to quantitatively analyze the effect of lumbar spinal muscle atrophy on the compressive (perpendicular to the upper surface of the disc) and shear (parallel to the upper surface of the disc in the anterior-posterior direction) forces change on lumbar intervertebral discs using a full body musculoskeletal modeling approach. Muscles atrophy was modeled with reduction of the functional cross-sectional area (FCSA) of the muscles. Compressive and shear forces under two levels of lumbar muscle atrophy (20% and 40%) at eight daily postures (lying on back, seating slouched, seating straight, standing, standing flexed (36°), standing lift a 20 kg weight close to chest, standing lift a 20 kg weight flexed (38°), and standing lift a 20 kg weight with arm stretched) were analyzed.

Effect of fixed charge density on water content of IVD during bed rest: A numerical analysis.

The fixed charge density (FCD) in the intervertebral disc (IVD) matrix is essential for its capacity of absorbing water, particularly during overnight bed rest. However, the FCD decreases with IVD degeneration, reducing the disc propensity to swell and the related convective transport of molecules across the IVDs. The objective of this study was to investigate the effects of the FCD on water intake in the IVD during bed rest.