Finite element modeling and simulation of degeneration and hydrotraction therapy of human lumbar spine segments

A large percent of population is affected by low back pain problems all over the world, starting from the degeneration of the lumbar spinal structure, caused generally by ageing and mechanical overloading. If the degeneration is not too advanced, surgical treatments can be avoid, by applying conservative treatments, like traction therapies. Dry traction is a well-known method, however, often happens that instead of the traction effect and stress relaxation, the compression increases in the discs due to muscle activities. This verifies the importance of the suspension hydro-traction therapy, where the muscles are completely relaxed. The aim of this study was doubled: to model and simulate numerically the age-related and accidental degenerations of lumbar functional spinal units (FSU) and to simulate the mechanical answer of the more or less degenerated lumbar segments for the hydro-traction treatment, by using FE method. The basic question was: how to unload the disc to regain or improve its functional and metabolic ability. FE simulations of the mechanical behaviour of human lumbar FSUs with life-long agerelated and sudden accidental degenerations are presented for tension and compression. Compressive material constants were obtained from the literature, tensional material moduli were determined by parameter identification, using in vivo measured global elongations of segments as control parameters. 3D FE models of a typical FSU of lumbar part L3-S1 were developed extended to several nonlinear and nonsmooth unilateral features of intervertebral discs, ligaments, articular facet joints and attachments. The FE model was validated both for compression and tension, by comparing the numerical calculations with experimental results. The weightbath hydrotraction therapy decreases pain, increases joint flexibility, and improves the quality of life of patients with cervical or lumbar discopathy. Numerical simulations were investigated to clear the biomechanical effects of hydrotraction treatment of more or less degenerated segments to improve the efficiency of the non-invasive conservative treatment

Intervertebral disc recovery after dynamic or static loading in vitro: Is there a role for the endplate?

Abstract In vivo studies on disc mechanics show loss of fluid from the intervertebral disc (IVD) during loading and full recovery during rest. Previous work indicated that in vitro recovery is hampered after static loading. The aim of the present study was to investigate the role of the endplate after dynamic and static loading on mechanical recovery in vitro. Lumbar spines (caprine) were obtained from the local slaughterhouse and stored frozen. Twenty-four intervertebral discs were thawed and subjected to a compression test in a saline bath (37 1C). The discs were pre-loaded at 20 N for 15 min. Three 15-min loading cycles (static: 2.0 MPa or dynamic: average load 2.0 MPa at 0.5 Hz) were applied, each followed by a 30-min period of unloading (20 N). After this protocol, the endplates of half of the discs were blocked with silicone paste and the long-term recovery protocol was applied; the discs were subjected to a single loading cycle (15 min of static or dynamic loading) followed by 10 h of unloading at 20 N. All specimens showed a net loss of height and a gain in stiffness during the first part of the test. Eventually, height and stiffness were restored during a long-term recovery test. The difference in recovery between blocked and free endplates was marginal. If fluid flow plays a role during recovery in vitro, the role of the endplate appears to be limited. Our findings show no influence of loading type on recovery in vitro.

Estimation of in vivo inter-vertebral loading during motion using fluoroscopic and magnetic resonance image informed finite element models

Finite element (FE) models driven by medical image data can be used to estimate subject-specific spinal biomechanics. This study aimed to combine magnetic resonance (MR) imaging and quantitative fluoroscopy (QF) in subject-specific FE models of upright standing, flexion and extension. Supine MR images of the lumbar spine were acquired from healthy participants using a 0.5 T MR scanner. Nine 3D quasi-static linear FE models of L3 to L5 were created with an elastic nucleus and orthotropic annulus. QF data was acquired from the same participants who performed trunk flexion to 60o and trunk extension to 20o. The displacements and rotations of the vertebrae were calculated and applied to the FE model. Stresses were averaged across the nucleus region and transformed to the disc co-ordinate system (S1 = mediolateral, S2 = anteroposterior, S3 = axial). In upright standing S3 was predicted to be -0.7 ± 0.6 MPa (L3L4) and -0.6 ± 0.5 MPa (L4L5). S3 increased to -2.0 ± 1.3 MPa (L3L4) and -1.2 ± 0.6 MPa (L4L5) in full flexion and to -1.1 ± 0.8 MPa (L3L4) and -0.7 ± 0.5 MPa (L4L5) in full extension. S1 and S2 followed similar patterns; shear was small apart from S23. Disc stresses correlated to disc orientation and wedging. The results demonstrate that MR and QF data can be combined in a participant-specific FE model to investigate spinal biomechanics in vivo and that predicted stresses are within ranges reported in the literature

In Situ Cell Signalling of the Hippo-YAP/TAZ Pathway in Reaction to Complex Dynamic Loading in an Intervertebral Disc Organ Culture

Recently, a dysregulation of the Hippo-YAP/TAZ pathway has been correlated with intervertebral disc (IVD) degeneration (IDD), as it plays a key role in cell survival, tissue regeneration, and mechanical stress. We aimed to investigate the influence of different mechanical loading regimes, i.e., under compression and torsion, on the induction and progression of IDD and its association with the Hippo-YAP/TAZ pathway. Therefore, bovine IVDs were assigned to one of four different static or complex dynamic loading regimes: (i) static, (ii) “low-stress”, (iii) “intermediate-stress”, and (iv) “high-stress” regime using a bioreactor. After one week of loading, a significant loss of relative IVD height was observed in the intermediate- and high-stress regimes. Furthermore, the high-stress regime showed a significantly lower cell viability and a significant decrease in glycosaminoglycan content in the tissue. Finally, the mechanosensitive gene CILP was significantly downregulated overall, and the Hippo-pathway gene MST1 was significantly upregulated in the high-stress regime. This study demonstrates that excessive torsion combined with compression leads to key features of IDD. However, the results indicated no clear correlation between the degree of IDD and a subsequent inactivation of the Hippo-YAP/TAZ pathway as a means of regenerating the IVD

The role of panx3 in age-associated and injury-induced intervertebral disc degeneration

© 2021 by the authors. Licensee MDPI, Basel, Switzerland. Pannexin 3 (Panx3) is a mechanosensitive, channel-forming glycoprotein implicated in the progression of post-traumatic osteoarthritis. Despite evidence for Panx3 expression in the intervertebral disc (IVD), its function in this cartilaginous joint structure remained unknown. Using Panx3 knockout mice, this study investigated the role of Panx3 in age-associated IVD degeneration and degeneration induced by annulus fibrosus (AF) needle puncture. Loss of Panx3 did not significantly impact the progression of age-associated histopathological IVD degeneration; however, loss of Panx3 was associated with decreased gene expression of Acan, Col1a1, Mmp13 and Runx2 and altered localization of COLX in the IVD at 19 months-of-age. Following IVD injury in the caudal spine, histological analysis of wild-type mice revealed clusters of hypertrophic cells in the AF associated with increased pericellular proteoglycan accumulation, disruptions in lamellar organization and increased lamellar thickness. In Panx3 knockout mice, hypertrophic AF cells were rarely detected and AF structure was largely preserved post-injury. Interestingly, uninjured IVDs adjacent to the site of injury more frequently showed evidence of early nucleus pulposus degeneration in Panx3 knockout mice but remained healthy in wild-type mice. These findings suggest a role for Panx3 in mediating the adaptive cellular responses to altered mechanical stress in the IVD, which may buffer aberrant loads transferred to adjacent motion segments

Digital tracking algorithm reveals the influence of structural irregularities on joint movements in the human cervical spine

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.clinbiomech.2018.04.015 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Background Disc height loss and osteophytes change the local mechanical environment in the spine; while previous research has examined kinematic dysfunction under degenerative change, none has looked at the influence of disc height loss and osteophytes throughout movement. Methods Twenty patients with pain related to the head, neck or shoulders were imaged via videofluoroscopy as they underwent sagittal-plane flexion and extension. A clinician graded disc height loss and osteophytes as “severe/moderate”, “mild”, or “none”. A novel tracking algorithm quantified motions of each vertebra. This information was used to calculate intervertebral angular and shear displacements. The digital algorithm made it practical to track individual vertebrae in multiple patients through hundreds of images without bias. Findings Cases without height loss/osteophytes had a consistent increase in intervertebral angular displacement from C2/C3 to C5/C6, like that of healthy individuals, and mild height losses did not produce aberrations that were systematic or necessarily discernable. However, joints with moderate to severe disc height loss and osteophytes exhibited reduced range of motion compared to adjacent unaffected joints in that patient and corresponding joints in patients without structural irregularities. Interpretation Digitally-obtained motion histories of individual joints allowed anatomical joint changes to be linked with changes in joint movement patterns. Specifically, disc height loss and osteophytes were found to influence cervical spine movement in the sagittal plane, reducing angular motions at affected joints by approximately 10% between those with and without height loss and osteophytes. Further, these joint changes were associated with perturbed intervertebral angular and shear movements.Natural Sciences and Engineering Research Council (NSERC) Discovery Grant

Significance of orientation and determination of cummulative damage measures during cyclic testing of human thoracolumbar spine.

Determining the mechanical properties of the spine is a significant step in understanding the behavior of the spine under normal conditions. Although a limited amount of data for cyclic loading is currently available, the tests are not completely documented and the loads, spine segment positioning, and frequency are not representative of those typically found during normal activities. The purpose of this study is to develop an understanding of the relationship between loads and the development of fatigue failure in thoracolumbar motion segments. Motion segments separated from human cadaveric spine were tested in two series. Compression series applied a pure compression load quasi-statically in the neutral position. The load was increased and the specimen was observed to determine failure. Motion segments were also tested without orientation (axially aligned). The results from the tests show that mechanical properties of the disc depend on the orientation of the motion segments at neutral angle. Results also suggest that energy dissipation could be potentially a good damage measure unlike creep

Back stress and assistance exercises in extreme weightlifting

The purpose or this study was to test the suitability or selected assistance exercises to strengthen the low back for the Olympic lilts in elite weightlifters. Four subjects were filmed by a five-camera Motion Analysis system operating at 120Hz. The subjects completed both or the Olympic lifts (Snatch and Clean) at a near one repetition maximum and four assistance exercises (Bent-over Row, Clean Pull Deadlift, Romanian Deadlift, and Good Morning) at an intensity typically performed at a routine training session. Peak moments, compressive and shear forces about the L5/S1 intervertebral joint were calculated via a top-down inverse dynamics model. Comparisons were made between the lifts using a one way ANOVA with repeated measures and post-hoc differences between the means were calculated via Least Squared Differences. Significant differences (