Effect of degeneration on the six degree of freedom mechanical properties of human lumbar spine segments

Abstract

While the effects of disc degeneration on compression and rotation motions have been studied, there is no data for shear loading. Clinical research has shown that those with low back pain (a potential consequence of degeneration) experience a 75% greater lateral shear force than those without it. Therefore, the aim was to compare the effect of degeneration on spine segment stiffness and phase angle in each of six degree of freedom (6DOF) loading directions. Fourteen intact functional spinal units (FSU) were dissected from human lumbar spines (mean (SD) age 76.2 (11) years, Thompson grades 3 (N ¼ 5, mild), 4 (N ¼ 6, moderate), 5 (N ¼ 3, severe)). Each FSU was tested in AE6DOFs while subjected to a physiological preload, hydration, and temperature (37˚C) conditions in a hexapod robot. A one-way ANOVA between degenerated groups was performed on stiffness and phase angle for each DOF. Significant differences in stiffness were found between mild and moderate degenerative groups in lateral shear (p ¼ 0.001), and axial rotation (p ¼ 0.001), where moderate degeneration had decreased stiffness. For phase angle, significant differences were seen in anterior shear (p ¼ 0.017), and axial rotation (p ¼ 0.026), where phase angle for mild degeneration was less than moderate. Trends of stiffness and phase angle changes between degenerative groups were similar within each DOF. Clinically, the identification of the DOFs that are most affected by degeneration could be used in rehabilitation to improve supplemental stabilization of core muscle groups. ß

Contribution of facet joints, axial compression, and composition to human lumbar disc torsion mechanics

“…Finally, a power analysis was conducted to determine the sample size required to perform correlations between torsion mechanics and tissue composition. Based on previous work on disc torsion mechanics, strong correlations were expected and this was taken into account in sample size estimation (input: ρ ≥ 0.80). Based on the results of all power analyses, nine discs were required to achieve the desired power and alpha level.…”

“…Structural and compositional changes, with injury or degeneration, alter stress distribution within the disc and between the disc and facet joints . These changes influence the mechanical properties of the disc joint, including its stiffness, range of motion, and energy absorption under quasi‐static and dynamic loads, and increase the likelihood of annular tears . For example, radial tears, which are precursors for herniated or bulging discs, reduce joint stiffness in torsion, lateral bending, flexion, and extension .…”

“…For example, radial tears, which are precursors for herniated or bulging discs, reduce joint stiffness in torsion, lateral bending, flexion, and extension . Mild to moderate degeneration has also been shown to decrease stiffness in torsion, but joint stiffness increases again with severe degeneration . Assessment of disc degeneration in these early studies has been largely limited to visual inspection of gross morphology or radiographic images; therefore, the relationship between tissue composition and torsion mechanics is not well understood.…”

Relevance of bioreactors and whole tissue cultures for the translation of new therapies to humans

“…32,33 Finally, there is the need to develop more physiological motion patterns, for instance by substituting axial compression with bending. Advanced systems comprising six degrees of freedom, such as the ones developed by the group of Costi et al to assess the mechanical behavior of human IVDs with varying degree of degeneration, 34 hold a great promise for the future.…”

New Horizons in Spine Research: Disc biology, spine biomechanics and pathomechanisms of back pain

“…Novel features of IVD structure and their functional roles are still being identified and the role of the inter‐lamellar matrix is clarified by Tavakoli et al Identifying early degenerative changes requires advanced imaging methods, their quantitation, and their validation in animal models . Effects of degeneration on human motion segment functional biomechanics are clarified in papers using advanced multi‐degree‐of‐freedom biomechanical testing methods, and Muruiki et al further identifies biomechanical changes with spinal level and sex . The endplate is receiving increasing attention and papers by Kishimoto et al and DeLucca et al, describe novel findings regarding their anatomy and changes with degeneration …”