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Gacek E, Ellingson AM, Barocas VH. Residual Strain and Joint Pressurization Maintain Collagen Tension for On-Joint Lumbar Facet Capsular Ligaments. J Biomech Eng 2024; 146:111005. [PMID: 39082759 PMCID: PMC11369690 DOI: 10.1115/1.4066091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 07/25/2024] [Indexed: 08/21/2024]
Abstract
Modeling the lumbar facet capsular ligament's (FCL) mechanical behavior under various physiological motions has often been a challenge due to limited knowledge about the on-joint in situ ligament state arising from attachment to the bone or other internal loads. Building on prior work, this study presents an enhanced computational model of the lumbar facet capsular ligament by incorporating residual strain and joint pressurization strain, factors neglected in prior models. Further, the model can predict strain and stress distribution across the ligament under various spinal motions, highlighting the influence of the ligament's attachment to the bone, internal synovial fluid pressurization, and distribution of collagen fiber alignment on the overall mechanical response of the ligament. Joint space inflation was found to influence the total observed stress and strain fields, both at rest and during motion. A significant portion of the ligament was found to be in tension, even in the absence of external load. Additionally, the model's ability to account for residual strain offers a more realistic portrayal of the collagen fibers and elastin matrix's role in ligament mechanics. We conclude that (1) computational models of the lumbar facet capsular ligament should not assume that the ligament is unloaded when the joint is in its neutral position, and (2) the ligament is nearly always in tension, which may be important in terms of its long-term growth and remodeling.
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Affiliation(s)
- Elizabeth Gacek
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN 55455
| | - Arin M Ellingson
- Divisions of Physical Therapy and Rehabilitation Science, Department of Rehabilitation Medicine, University of Minnesota - Twin Cities, Minneapolis, MN 55455
| | - Victor H Barocas
- Department of Biomedical Engineering, University of Minnesota - Twin Cities, Minneapolis, MN 55455
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Nikpasand M, Abbott RE, Kage CC, Singh S, Winkelstein BA, Barocas VH, Ellingson AM. Cervical facet capsular ligament mechanics: Estimations based on subject-specific anatomy and kinematics. JOR Spine 2023; 6:e1269. [PMID: 37780821 PMCID: PMC10540825 DOI: 10.1002/jsp2.1269] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 05/30/2023] [Accepted: 06/02/2023] [Indexed: 10/03/2023] Open
Abstract
Background To understand the facet capsular ligament's (FCL) role in cervical spine mechanics, the interactions between the FCL and other spinal components must be examined. One approach is to develop a subject-specific finite element (FE) model of the lower cervical spine, simulating the motion segments and their components' behaviors under physiological loading conditions. This approach can be particularly attractive when a patient's anatomical and kinematic data are available. Methods We developed and demonstrated methodology to create 3D subject-specific models of the lower cervical spine, with a focus on facet capsular ligament biomechanics. Displacement-controlled boundary conditions were applied to the vertebrae using kinematics extracted from biplane videoradiography during planar head motions, including axial rotation, lateral bending, and flexion-extension. The FCL geometries were generated by fitting a surface over the estimated ligament-bone attachment regions. The fiber structure and material characteristics of the ligament tissue were extracted from available human cervical FCL data. The method was demonstrated by application to the cervical geometry and kinematics of a healthy 23-year-old female subject. Results FCL strain within the resulting subject-specific model were subsequently compared to models with generic: (1) geometry, (2) kinematics, and (3) material properties to assess the effect of model specificity. Asymmetry in both the kinematics and the anatomy led to asymmetry in strain fields, highlighting the importance of patient-specific models. We also found that the calculated strain field was largely independent of constitutive model and driven by vertebrae morphology and motion, but the stress field showed more constitutive-equation-dependence, as would be expected given the highly constrained motion of cervical FCLs. Conclusions The current study provides a methodology to create a subject-specific model of the cervical spine that can be used to investigate various clinical questions by coupling experimental kinematics with multiscale computational models.
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Affiliation(s)
- Maryam Nikpasand
- Department of Mechanical EngineeringUniversity of Minnesota—Twin CitiesMinneapolisMinnesotaUSA
| | - Rebecca E. Abbott
- Department of Rehabilitation MedicineUniversity of Minnesota—Twin CitiesMinneapolisMinnesotaUSA
| | - Craig C. Kage
- Department of Rehabilitation MedicineUniversity of Minnesota—Twin CitiesMinneapolisMinnesotaUSA
| | - Sagar Singh
- Department of BioengineeringUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
| | - Beth A. Winkelstein
- Department of BioengineeringUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
| | - Victor H. Barocas
- Department of Mechanical EngineeringUniversity of Minnesota—Twin CitiesMinneapolisMinnesotaUSA
- Department of Biomedical EngineeringUniversity of Minnesota—Twin CitiesMinneapolisMinnesotaUSA
| | - Arin M. Ellingson
- Department of Rehabilitation MedicineUniversity of Minnesota—Twin CitiesMinneapolisMinnesotaUSA
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Meszaros-Beller L, Hammer M, Riede JM, Pivonka P, Little JP, Schmitt S. Effects of geometric individualisation of a human spine model on load sharing: neuro-musculoskeletal simulation reveals significant differences in ligament and muscle contribution. Biomech Model Mechanobiol 2023; 22:669-694. [PMID: 36602716 PMCID: PMC10097810 DOI: 10.1007/s10237-022-01673-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Accepted: 12/08/2022] [Indexed: 01/06/2023]
Abstract
In spine research, two possibilities to generate models exist: generic (population-based) models representing the average human and subject-specific representations of individuals. Despite the increasing interest in subject specificity, individualisation of spine models remains challenging. Neuro-musculoskeletal (NMS) models enable the analysis and prediction of dynamic motions by incorporating active muscles attaching to bones that are connected using articulating joints under the assumption of rigid body dynamics. In this study, we used forward-dynamic simulations to compare a generic NMS multibody model of the thoracolumbar spine including fully articulated vertebrae, detailed musculature, passive ligaments and linear intervertebral disc (IVD) models with an individualised model to assess the contribution of individual biological structures. Individualisation was achieved by integrating skeletal geometry from computed tomography and custom-selected muscle and ligament paths. Both models underwent a gravitational settling process and a forward flexion-to-extension movement. The model-specific load distribution in an equilibrated upright position and local stiffness in the L4/5 functional spinal unit (FSU) is compared. Load sharing between occurring internal forces generated by individual biological structures and their contribution to the FSU stiffness was computed. The main finding of our simulations is an apparent shift in load sharing with individualisation from an equally distributed element contribution of IVD, ligaments and muscles in the generic spine model to a predominant muscle contribution in the individualised model depending on the analysed spine level.
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Affiliation(s)
- Laura Meszaros-Beller
- School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Brisbane, Australia.,Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
| | - Maria Hammer
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany.,Stuttgart Center for Simulation Science (SC SimTech), University of Stuttgart, Stuttgart, Germany
| | - Julia M Riede
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
| | - Peter Pivonka
- School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Brisbane, Australia
| | - J Paige Little
- School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Brisbane, Australia
| | - Syn Schmitt
- School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Brisbane, Australia. .,Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany. .,Stuttgart Center for Simulation Science (SC SimTech), University of Stuttgart, Stuttgart, Germany.
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Prado M, Mascoli C, Giambini H. Discectomy decreases facet joint distance and increases the instability of the spine: A finite element study. Comput Biol Med 2022; 143:105278. [PMID: 35124438 DOI: 10.1016/j.compbiomed.2022.105278] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 01/24/2022] [Accepted: 01/28/2022] [Indexed: 11/03/2022]
Abstract
The L4-L5 spinal segment is mostly associated with the development of lumbar back pain (LBP). Lumbar disc herniation (LDH), intervertebral disc degeneration (IVDD), or degeneration of the facet joints (FJs) can lead to LBP. Although the surgical gold standard for treating LDH is well established, consequences from this surgery on the biomechanics of the spine are still a matter of discussion. Using a finite element model of the L4-L5 spinal segment, this study aimed (1) to determine the changes in FJ distance during physiological motions of a lumbar spine in a healthy-normal condition, after conservative and aggressive percutaneous transforaminal endoscopic discectomy (PTED) to correct LDH, and during mild and severe IVDD; (2) to determine spine instability and endplate stresses under various physiological motions. Aggressive-PTED in a healthy disc decreased facet distances in axial rotation, lateral bending, and flexion by ∼25%, ∼10%, and 8%, respectively. Mild and severe disc degeneration increased the stiffness of the spine, resulting in a decrease in the range of motion (ROM) for all conditions. Severe disc degeneration decreased ROM as high as 57% for lateral bending, while a 13% decrease was observed for mild degeneration. High and abnormal endplate stress distributions were observed due to PTED and IVDD. PTED and IVDD, individually and collectively, change spine kinematics potentially leading to LBP and other associated negative outcomes. An increase in spine instability and a decrease in distance between superior and inferior facets resulting from PTED might lead to facet degeneration.
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Affiliation(s)
- Maria Prado
- Department of Biomedical Engineering and Chemical Engineering, University of Texas at San Antonio, San Antonio, TX, USA
| | - Caroline Mascoli
- Biomedical Engineering Department, University of Connecticut, Storrs, CT, USA
| | - Hugo Giambini
- Department of Biomedical Engineering and Chemical Engineering, University of Texas at San Antonio, San Antonio, TX, USA.
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Gacek E, Bermel EA, Ellingson AM, Barocas VH. Through-thickness regional variation in the mechanical characteristics of the lumbar facet capsular ligament. Biomech Model Mechanobiol 2021; 20:1445-1457. [PMID: 33788068 PMCID: PMC9289988 DOI: 10.1007/s10237-021-01455-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Accepted: 03/25/2021] [Indexed: 10/21/2022]
Abstract
The human lumbar facet capsule, with the facet capsular ligament (FCL) that forms its primary constituent, is a common source of lower back pain. Prior studies on the FCL were limited to in-plane tissue behavior, but due to the presence of two distinct yet mechanically different regions, a novel out-of-plane study was conducted to further characterize the roles of the collagen and elastin regions. An experimental technique, called stretch-and-bend, was developed to study the tension-compression asymmetry of the FCL due to varying collagen fiber density throughout the thickness of the tissue. Each healthy excised cadaveric FCL sample was tested in four conditions depending on primary collagen fiber alignment and regional loading. Our results indicate that the FCL is stiffest when the collagen fibers (1) are aligned in the direction of loading, (2) are in tension, and (3) are stretched - 16% from its off-the-bone, undeformed state. An optimization routine was used to fit a four-parameter anisotropic, hyperplastic model to the experimental data. The average elastin modulus, E, and the average collagen fiber modulus, ξ, were 13.15 ± 3.59 kPa and 18.68 ± 13.71 MPa (95% CI), respectively.
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Affiliation(s)
- Elizabeth Gacek
- Biomedical Engineering, University of Minnesota, 312 Church St. SE, 7-105 Nils Hasselmo Hall, Minneapolis, MN, 55455, USA
| | - Emily A Bermel
- Biomedical Engineering, University of Minnesota, 312 Church St. SE, 7-105 Nils Hasselmo Hall, Minneapolis, MN, 55455, USA
| | - Arin M Ellingson
- Divisions of Physical Therapy and Rehabilitation Science, Departments of Rehabilitation Medicine and Orthopedic Surgery, University of Minnesota, 426 Church St. SE, 366A Children's Rehab Ctr, Minneapolis, MN, 55455, USA
| | - Victor H Barocas
- Biomedical Engineering, University of Minnesota, 312 Church St. SE, 7-105 Nils Hasselmo Hall, Minneapolis, MN, 55455, USA.
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Nikpasand M, Mahutga RR, Bersie-Larson LM, Gacek E, Barocas VH. A Hybrid Microstructural-Continuum Multiscale Approach for Modeling Hyperelastic Fibrous Soft Tissue. JOURNAL OF ELASTICITY 2021; 145:295-319. [PMID: 36380845 PMCID: PMC9648697 DOI: 10.1007/s10659-021-09843-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 05/19/2021] [Indexed: 06/16/2023]
Abstract
The heterogeneous, nonlinear, anisotropic material behavior of biological tissues makes precise definition of an accurate constitutive model difficult. One possible solution to this issue would be to define microstructural elements and perform fully coupled multiscale simulation. However, for complex geometries and loading scenarios, the computational costs of such simulations can be prohibitive. Ideally then, we should seek a method that contains microstructural detail, but leverages the speed of classical continuum-based finite-element (FE) modeling. In this work, we demonstrate the use of the Holzapfel-Gasser-Ogden (HGO) model [1, 2] to fit the behavior of microstructural network models. We show that Delaunay microstructural networks can be fit to the HGO strain energy function by calculating fiber network strain energy and average fiber stretch ratio. We then use the HGO constitutive model in a FE framework to improve the speed of our hybrid model, and demonstrate that this method, combined with a material property update scheme, can match a full multiscale simulation. This method gives us flexibility in defining complex FE simulations that would be impossible, or at least prohibitively time consuming, in multiscale simulation, while still accounting for microstructural heterogeneity.
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Affiliation(s)
- Maryam Nikpasand
- Department of Mechanical Engineering, University of Minnesota – Twin Cities, Minneapolis, MN, USA
| | - Ryan R. Mahutga
- Department of Biomedical Engineering, University of Minnesota – Twin Cities, Minneapolis, MN, USA
| | - Lauren M. Bersie-Larson
- Department of Biomedical Engineering, University of Minnesota – Twin Cities, Minneapolis, MN, USA
| | - Elizabeth Gacek
- Department of Biomedical Engineering, University of Minnesota – Twin Cities, Minneapolis, MN, USA
| | - Victor H. Barocas
- Department of Biomedical Engineering, University of Minnesota – Twin Cities, Minneapolis, MN, USA
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