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Muñoz-Moya E, Rasouligandomani M, Ruiz Wills C, Chemorion FK, Piella G, Noailly J. Unveiling interactions between intervertebral disc morphologies and mechanical behavior through personalized finite element modeling. Front Bioeng Biotechnol 2024; 12:1384599. [PMID: 38915337 PMCID: PMC11194671 DOI: 10.3389/fbioe.2024.1384599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Accepted: 04/25/2024] [Indexed: 06/26/2024] Open
Abstract
Introduction: Intervertebral Disc (IVD) Degeneration (IDD) is a significant health concern, potentially influenced by mechanotransduction. However, the relationship between the IVD phenotypes and mechanical behavior has not been thoroughly explored in local morphologies where IDD originates. This work unveils the interplays among morphological and mechanical features potentially relevant to IDD through Abaqus UMAT simulations. Methods: A groundbreaking automated method is introduced to transform a calibrated, structured IVD finite element (FE) model into 169 patient-personalized (PP) models through a mesh morphing process. Our approach accurately replicates the real shapes of the patient's Annulus Fibrosus (AF) and Nucleus Pulposus (NP) while maintaining the same topology for all models. Using segmented magnetic resonance images from the former project MySpine, 169 models with structured hexahedral meshes were created employing the Bayesian Coherent Point Drift++ technique, generating a unique cohort of PP FE models under the Disc4All initiative. Machine learning methods, including Linear Regression, Support Vector Regression, and eXtreme Gradient Boosting Regression, were used to explore correlations between IVD morphology and mechanics. Results: We achieved PP models with AF and NP similarity scores of 92.06\% and 92.10\% compared to the segmented images. The models maintained good quality and integrity of the mesh. The cartilage endplate (CEP) shape was represented at the IVD-vertebra interfaces, ensuring personalized meshes. Validation of the constitutive model against literature data showed a minor relative error of 5.20%. Discussion: Analysis revealed the influential impact of local morphologies on indirect mechanotransduction responses, highlighting the roles of heights, sagittal areas, and volumes. While the maximum principal stress was influenced by morphologies such as heights, the disc's ellipticity influenced the minimum principal stress. Results suggest the CEPs are not influenced by their local morphologies but by those of the AF and NP. The generated free-access repository of individual disc characteristics is anticipated to be a valuable resource for the scientific community with a broad application spectrum.
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Affiliation(s)
- Estefano Muñoz-Moya
- BCN MedTech, Department of Engineering, Universitat Pompeu Fabra, Barcelona, Spain
| | | | - Carlos Ruiz Wills
- BCN MedTech, Department of Engineering, Universitat Pompeu Fabra, Barcelona, Spain
| | - Francis Kiptengwer Chemorion
- BCN MedTech, Department of Engineering, Universitat Pompeu Fabra, Barcelona, Spain
- Department of Information Technology, InSilicoTrials Technologies, Trieste, Italy
| | - Gemma Piella
- BCN MedTech, Department of Engineering, Universitat Pompeu Fabra, Barcelona, Spain
| | - Jérôme Noailly
- BCN MedTech, Department of Engineering, Universitat Pompeu Fabra, Barcelona, Spain
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Zhang C, Guo LX. Effect of whole-body vibration at different frequencies on the lumbar spine: A finite element study based on a whole human body model. Proc Inst Mech Eng H 2022; 236:1752-1761. [DOI: 10.1177/09544119221135688] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Many previous studies have found that occupational drivers commonly suffered from low back pain, and low back pain and degeneration of the intervertebral disc might be associated with vibration conditions. However, the biomechanical mechanisms of whole-body vibration that caused pain and injury were not clear. In this study, a validated whole human body finite element model was used, and vibration loads at frequencies of 3, 5, 7 and 9 Hz were loaded to evaluate the frequency effects on the spine. The results showed that the responses of the spine were strong at the 5 Hz vibration load. Vibration loads would produce alternating stresses and bulges in the annulus fibrosus and change the direction of the pressure in the nucleus pulposus. The posterior region of the intervertebral disc showed greater stress fluctuations than the anterior region. The Risk Factors showed that long-term exposure to whole-body vibrations at 5 and 7 Hz might have greater adverse effects on the spine. The findings of this study confirmed that vibrations near the resonance frequency of the human body would cause more injuries to the spine than other frequencies. Alternating stress and bulge might cause fatigue and the degeneration of the intervertebral disc, which might be the mechanisms of spinal injury caused by whole-body vibration, and the posterior regions of the intervertebral disc were more susceptible to degeneration. Some appropriate measures should be taken to reduce the adverse effects of whole-body vibration on spinal health.
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Affiliation(s)
- Chi Zhang
- School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China
| | - Li-Xin Guo
- School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China
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The Radial Bulging and Axial Strains of Intervertebral Discs during Creep Obtained with the 3D-DIC System. Biomolecules 2022; 12:biom12081097. [PMID: 36008991 PMCID: PMC9405674 DOI: 10.3390/biom12081097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2022] [Revised: 08/01/2022] [Accepted: 08/06/2022] [Indexed: 11/16/2022] Open
Abstract
Creep-associated changes in disc bulging and axial strains are essential for the research and development of mechano-bionic biomaterials and have been assessed in various ways in ex vivo creep studies. Nonetheless, the reported methods for measurement were limited by location inaccuracy, a lack of synchronousness, and destructiveness. To this end, this study focuses on the accurate, synchronous, and noninvasive assessment of bugling and strains using the 3D digital image correlation (3D-DIC) system and the impact of creep on them. After a preload of 30 min, the porcine cervical discs were loaded with different loads for 4 h of creep. Axial strains and lateral bulging of three locations on the discs were synchronously measured. The three-parameter solid model and the newly proposed horizontal asymptote models were used to fit the acquired data. The results showed that the load application reduced disc strains by 6.39% under 300 N, 11.28% under 400 N, and 12.59% under 500 N. Meanwhile, the largest protrusion occurred in the middle of discs with a bugling of 1.50 mm, 1.67 mm, and 1.87 mm. Comparison of the peer results showed that the 3D-DIC system could be used in ex vivo biomechanical studies with reliability and had potential in the assessment of the mechanical behavior of novel biomaterials. The phenomenon of the largest middle protrusion enlightened further the strength of spinal implants in this area. The mathematical characterizations of bulging and strains under different loads yielded various model parameters, which are prerequisites for developing implanted biomaterials.
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Mengoni M, Zapata-Cornelio FY, Wijayathunga VN, Wilcox RK. Experimental and Computational Comparison of Intervertebral Disc Bulge for Specimen-Specific Model Evaluation Based on Imaging. Front Bioeng Biotechnol 2021; 9:661469. [PMID: 34124021 PMCID: PMC8193738 DOI: 10.3389/fbioe.2021.661469] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Accepted: 04/27/2021] [Indexed: 11/13/2022] Open
Abstract
Finite element modelling of the spinal unit is a promising preclinical tool to assess the biomechanical outcome of emerging interventions. Currently, most models are calibrated and validated against range of motion and rarely directly against soft-tissue deformation. The aim of this contribution was to develop an in vitro methodology to measure disc bulge and assess the ability of different specimen-specific modelling approaches to predict disc bulge. Bovine bone-disc-bone sections (N = 6) were prepared with 40 glass markers on the intervertebral disc surface. These were initially magnetic resonance (MR)-imaged and then sequentially imaged using peripheral-qCT under axial compression of 1 mm increments. Specimen-specific finite-element models were developed from the CT data, using three different methods to represent the nucleus pulposus geometry with and without complementary use of the MR images. Both calibrated specimen-specific and averaged compressive material properties for the disc tissues were investigated. A successful methodology was developed to quantify the disc bulge in vitro, enabling observation of surface displacement on qCT. From the finite element model results, no clear advantage was found in using geometrical information from the MR images in terms of the models' ability to predict stiffness or disc bulge for bovine intervertebral disc.
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Affiliation(s)
- Marlène Mengoni
- School of Mechanical Engineering, Institute of Medical and Biological Engineering, University of Leeds, Leeds, United Kingdom
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Costi JJ, Ledet EH, O'Connell GD. Spine biomechanical testing methodologies: The controversy of consensus vs scientific evidence. JOR Spine 2021; 4:e1138. [PMID: 33778410 PMCID: PMC7984003 DOI: 10.1002/jsp2.1138] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/01/2020] [Revised: 12/04/2020] [Accepted: 12/07/2020] [Indexed: 12/14/2022] Open
Abstract
Biomechanical testing methodologies for the spine have developed over the past 50 years. During that time, there have been several paradigm shifts with respect to techniques. These techniques evolved by incorporating state-of-the-art engineering principles, in vivo measurements, anatomical structure-function relationships, and the scientific method. Multiple parametric studies have focused on the effects that the experimental technique has on outcomes. As a result, testing methodologies have evolved, but there are no standard testing protocols, which makes the comparison of findings between experiments difficult and conclusions about in vivo performance challenging. In 2019, the international spine research community was surveyed to determine the consensus on spine biomechanical testing and if the consensus opinion was consistent with the scientific evidence. More than 80 responses to the survey were received. The findings of this survey confirmed that while some methods have been commonly adopted, not all are consistent with the scientific evidence. This review summarizes the scientific literature, the current consensus, and the authors' recommendations on best practices based on the compendium of available evidence.
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Affiliation(s)
- John J. Costi
- Biomechanics and Implants Research Group, Medical Device Research Institute, College of Science and EngineeringFlinders UniversityAdelaideAustralia
| | - Eric H. Ledet
- Department of Biomedical EngineeringRensselaer Polytechnic InstituteTroyNew YorkUSA
- Research and Development ServiceStratton VA Medical CenterAlbanyNew YorkUSA
| | - Grace D. O'Connell
- Department of Mechanical EngineeringUniversity of California‐BerkeleyBerkeleyCaliforniaUSA
- Department of Orthopaedic SurgeryUniversity of California‐San FranciscoSan FranciscoCaliforniaUSA
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Son S, Lee SG, Kim WK, Ahn Y, Jung JM. Disc height discrepancy between supine and standing positions as a screening metric for discogenic back pain in patients with disc degeneration. Spine J 2021; 21:71-79. [PMID: 32687982 DOI: 10.1016/j.spinee.2020.07.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 07/14/2020] [Accepted: 07/14/2020] [Indexed: 02/03/2023]
Abstract
BACKGROUND CONTEXT The diagnosis of discogenic low back pain (LBP) from disc degeneration of the lumbar spine is often evaluated with discography. Noninvasive, simple screening methods other than invasive discography are useful, as evidence supporting clinical findings and magnetic resonance imaging (MRI) have come to the forefront. PURPOSE To investigate disc height (DH) discrepancy between supine and standing positions on simple radiography to clarify its clinical screening value in individuals with discogenic LBP. STUDY DESIGN/SETTINGS Retrospective matched cohort design. PATIENT SAMPLE Ninety-two patients with early to middle stage disc degeneration (Pfirrmann grade II, III, or IV). OUTCOME MEASURES Each subject underwent simple radiographs and MRI. Baseline characteristics, including demographic data and MRI findings, and radiological findings, including DH discrepancy, segmental angle, and sagittal balance, were analyzed. DH discrepancy ratio was calculated as (1 - [calibrated DH on standing radiography/calibrated DH on supine radiography]) × 100%. METHODS We matched LBP group of 46 patients with intractable discogenic pain (≥7 of visual analog scale scores) confirmed by discography with control group of 46 patients with similar stage disc degeneration with mild LBP (≤4 of visual analog scale scores). Binary regression analysis, receiver operating characteristic curve analysis, and cut-off value for diagnosis were used to evaluate and clarify diagnostic value of various factors. RESULTS There was no significant difference between the two groups in terms of baseline characteristics, including age, sex, body mass index, pathological level, and magnetic resonance findings such as disc degeneration, high intensity zone, and para-spinal muscle volume. Among the various radiological findings, the calibrated mean DH in the standing position (20.87±5.65 [LBP group] vs. 26.95±3.02 [control group], p<.001) and the DH discrepancy ratio (14.55±6.13% [LBP group] vs. 1.47±0.75% [control group], p=.007) were significantly different between the two groups. The cut-off value for DH discrepancy ratio to screen discogenic LBP was ≥6.04%. Additionally, as a compensation for pain, sagittal vertical axis (3.43±2.03 cm [LBP group] vs. -0.54±3.05 cm [control group], p=.002) and pelvic incidence (54.74±6.76° [LBP group] vs. 43.98±8.67° [control group]; p=.006) were different between the two groups. CONCLUSIONS The results suggest that DH discrepancy between the supine and standing positions could be a screening metric for discogenic LBP in early to middle stage disc degeneration of the lumbar spine.
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Affiliation(s)
- Seong Son
- Department of Neurosurgery, Gil Medical Center, Gachon University College of Medicine, Nadong-Gu, Incheon, 21565, South Korea.
| | - Sang Gu Lee
- Department of Neurosurgery, Gil Medical Center, Gachon University College of Medicine, Nadong-Gu, Incheon, 21565, South Korea
| | - Woo Kyung Kim
- Department of Neurosurgery, Gil Medical Center, Gachon University College of Medicine, Nadong-Gu, Incheon, 21565, South Korea
| | - Yong Ahn
- Department of Neurosurgery, Gil Medical Center, Gachon University College of Medicine, Nadong-Gu, Incheon, 21565, South Korea
| | - Jong Myung Jung
- Department of Neurosurgery, Gil Medical Center, Gachon University College of Medicine, Nadong-Gu, Incheon, 21565, South Korea
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Castro APG, Alves JL. Numerical implementation of an osmo-poro-visco-hyperelastic finite element solver: application to the intervertebral disc. Comput Methods Biomech Biomed Engin 2020; 24:538-550. [PMID: 33111576 DOI: 10.1080/10255842.2020.1839059] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
This work deals with the finite element (FE) implementation of a biphasic poroelastic formulation specifically developed to address the intricate behaviour of the Intervertebral Disc (IVD) and other highly hydrated soft tissues. This formulation is implemented in custom FE solver V-Biomech, being the validation performed with a lumbar IVD model, which was compared against the analogous FE model of Williams et al. and the experiments of Tyrrell et al. Good agreement with these benchmarks was achieved, meaning that V-Biomech and its novel poroelastic formulation are a viable alternative for simulation of biphasic soft tissues.
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Affiliation(s)
- A P G Castro
- IDMEC - Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
| | - J L Alves
- CMEMs, Department of Mechanical Engineering, Universidade do Minho, Guimarães, Portugal
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Hassan CR, Lee W, Komatsu DE, Qin YX. Evaluation of nucleus pulposus fluid velocity and pressure alteration induced by cartilage endplate sclerosis using a poro-elastic finite element analysis. Biomech Model Mechanobiol 2020; 20:281-291. [PMID: 32949306 DOI: 10.1007/s10237-020-01383-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 09/01/2020] [Indexed: 11/25/2022]
Abstract
The nucleus pulposus (NP) in the intervertebral disk (IVD) depends on diffusive fluid transport for nutrients through the cartilage endplate (CEP). Disruption in fluid exchange of the NP is considered a cause of IVD degeneration. Furthermore, CEP calcification and sclerosis are hypothesized to restrict fluid flow between the NP and CEP by decreasing permeability and porosity of the CEP matrix. We performed a finite element analysis of an L3-L4 lumbar functional spine unit with poro-elastic constitutive equations. The aim of the study was to predict changes in the solid and fluid parameters of the IVD and CEP under structural changes in CEP. A compressive load of 500 N was applied followed by a 10 Nm moment in extension, flexion, lateral bending, and axial rotation to the L3-L4 model with fully saturated IVD, CEP, and cancellous bone. A healthy case of L3-L4 physiology was then compared to two cases of CEP sclerosis: a calcified cartilage endplate and a fluid constricted sclerotic cartilage endplate. Predicted NP fluid velocity increased for the calcified CEP and decreased for the calcified + less permeable CEP. Decreased NP fluid velocity was prominent in the axial direction through the CEP due to a less permeable path available for fluid flux. Fluid pressure and maximum principal stress in the NP were predicted to increase in both cases of CEP sclerosis compared to the healthy case. The porous medium predictions of this analysis agree with the hypothesis that CEP sclerosis decreases fluid flow out of the NP, builds up fluid pressure in the NP, and increases the stress concentrations in the NP solid matrix.
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Affiliation(s)
- Chaudhry Raza Hassan
- Department of Biomedical Engineering, Stony Brook University, 215 Bioengineering Building, Stony Brook, NY, 11794, USA
| | - Wonsae Lee
- Department of Biomedical Engineering, Stony Brook University, 215 Bioengineering Building, Stony Brook, NY, 11794, USA
| | - David Edward Komatsu
- Department of Orthopaedics, School of Medicine, Stony Brook University, Stony Brook, NY, USA
| | - Yi-Xian Qin
- Department of Biomedical Engineering, Stony Brook University, 215 Bioengineering Building, Stony Brook, NY, 11794, USA.
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Fewster KM, Haider S, Gooyers CE, Callaghan J, Wong A. A computerised system for measurement of the radial displacement of the intervertebral disc using a laser scanning device. COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING: IMAGING & VISUALIZATION 2019. [DOI: 10.1080/21681163.2019.1674189] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Kayla M. Fewster
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada
| | - Shahid Haider
- Department of Systems Design Engineering, University of Waterloo Faculty of Engineering, Waterloo, Ontario, Canada
| | | | - Jack Callaghan
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada
| | - Alexander Wong
- Department of Systems Design Engineering, University of Waterloo Faculty of Engineering, Waterloo, Ontario, Canada
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A biomechanical investigation of thoracolumbar burst fracture under vertical impact loads using finite element method. Clin Biomech (Bristol, Avon) 2019; 68:29-36. [PMID: 31146081 DOI: 10.1016/j.clinbiomech.2019.05.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 04/09/2019] [Accepted: 05/10/2019] [Indexed: 02/07/2023]
Abstract
BACKGROUND A sudden vertical impact load on spine can cause spinal burst fracture, especially in the thoracolumbar junction region. This study aimed at investigating the mechanism of spinal burst fracture under different energy vertical impact loads, producing the failure risk region to understand burst fracture, reducing nervous system damage and guiding clinical treatment. METHODS A nonlinear finite element model of T12-L1 motion segment was created to analyze the response of the vertical impact load. A rigid ball was used to impact the segment vertically to simulate the vertical impact load in practice. There were three different mass balls to represent the different loads: low energy, intermediate energy and high energy (respectively 13 J, 30 J and 56 J). The results of impact force, vertical displacement, stress, intradiscal pressure and contact force were obtained during the process. FINDINGS At low energy condition, the rigid ball rebounded rapidly. At intermediate energy condition, fractures were initiated in vertebral foramen and left rear regions on the superior cortical bone near the superior endplate of L1. At high energy condition, burst fracture occurred and a part of L1 was isolated from the model. INTERPRETATION The fracture occurred on the L1 segment only at the intermediate energy and high energy. The strength of vertebral body under low and intermediate energy was enough to support the impact. The burst fracture pattern at high energy was also observed in clinical practice. The findings may explain the mechanism of burst fracture.
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Presentation of an Approach on Determination of the Natural Frequency of Human Lumbar Spine Using Dynamic Finite Element Analysis. Appl Bionics Biomech 2019; 2019:5473891. [PMID: 30719072 PMCID: PMC6334357 DOI: 10.1155/2019/5473891] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 10/25/2018] [Accepted: 11/06/2018] [Indexed: 11/18/2022] Open
Abstract
Occurring resonance may negatively affect the health of the human lumbar spine. Hence, vibration generated in working and living environments should be optimized to avoid resonance when identifying the natural frequency of the human lumbar spine. The range of the natural frequency of the human lumbar spine has been investigated, but its specific numerical value has not been determined yet. This study aimed at presenting an approach based on resonance for predicting the specific numerical value of the natural frequency of the human lumbar spine. The changes in the numerical fluctuation amplitudes and the cycles of lumbar mechanical parameters during resonance are greater than those during nonresonant vibration. Given that the range of the natural frequency has been identified, vibrations at different excitation frequencies within this range can be applied in a human lumbar finite element model for dynamic finite element analysis. When the excitation frequency is close to the natural frequency, resonance occurs, causing great changes in the numerical fluctuation amplitudes and the cycles of lumbar mechanical parameters. Therefore, the natural frequency of the lumbar finite element model could be back-calculated. Results showed that the natural frequency of the established model was 3.5 Hz. Meanwhile, the closer the excitation frequency was to the natural frequency, the greater the changes in the numerical fluctuation amplitudes and cycles in the parameters would be. This study presented an approach for predicting the specific numerical value of the natural frequency of the human lumbar spine. Identifying the natural frequency assists in finding preventive measures for lumbar injury caused by vibration and in designing the vibration source in working and living environments to avoid approximating to the natural frequency of the human lumbar spine.
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Finite Element Investigation of the Effects of the Low-Frequency Vibration Generated by Vehicle Driving on the Human Lumbar Mechanical Properties. BIOMED RESEARCH INTERNATIONAL 2018; 2018:7962414. [PMID: 30364013 PMCID: PMC6186348 DOI: 10.1155/2018/7962414] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 09/05/2018] [Accepted: 09/16/2018] [Indexed: 11/17/2022]
Abstract
Long-term exposure to low-frequency vibration generated by vehicle driving impairs human lumbar spine health. However, few studies have investigated how low-frequency vibration affects human lumbar mechanical properties. This study established a poroelastic finite element model of human lumbar spinal segments L2–L3 to perform time-dependent vibrational simulation analysis and investigated the effects of different vibrational frequencies generated by normal vehicle driving on the lumbar mechanical properties in one hour. Analysis results showed that vibrational load caused more injury to lumbar health than static load, and vibration at the resonant frequency generated the most serious injury. The axial effective stress and the radial displacement in the intervertebral disc, as well as the fluid loss in the nucleus pulposus, increased, whereas the pore pressure in the nucleus pulposus decreased with increased vibrational frequency under the same vibrational time, which may aggravate the injury degree of human lumbar spine. Therefore, long-term driving on a well-paved road also induces negative effects on human lumbar spine health. When driving on a nonpaved road or operating engineering machinery under poor navigating condition, the auto seat transmits relatively high vibrational frequency, which is highly detrimental to the lumbar spine health of a driver.
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Szkoda-Poliszuk K, Żak M, Pezowicz C. Finite element analysis of the influence of three-joint spinal complex on the change of the intervertebral disc bulge and height. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2018; 34:e3107. [PMID: 29799170 DOI: 10.1002/cnm.3107] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2017] [Revised: 04/02/2018] [Accepted: 05/18/2018] [Indexed: 06/08/2023]
Abstract
This study evaluated the changes of height and bulging occurring in individual layers of the annulus fibrosus of the intervertebral disc for 3 load scenarios (axial compression, flexion, and extension). The numerical model of a single motion segment of the thoracic spine was analysed for 2 different configurations, ie, for the model of a physiological segment and a segment with the posterior column removed. In the physiological segment, all annulus fibrosus layers decrease in height regardless of the applied load, bulging outside the intervertebral disc. Removal of the posterior column increases mobility and disrupts the load transfer system, with the lamellae bulging into the intervertebral disc.
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Affiliation(s)
- Klaudia Szkoda-Poliszuk
- Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Faculty of Mechanical Engineering, Wroclaw University of Science and Technology, Wrocław, Poland
| | - Małgorzata Żak
- Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Faculty of Mechanical Engineering, Wroclaw University of Science and Technology, Wrocław, Poland
| | - Celina Pezowicz
- Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Faculty of Mechanical Engineering, Wroclaw University of Science and Technology, Wrocław, Poland
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Khalaf K, Nikkhoo M, Parnianpour M, Campbell-Kyureghyan N, Haghpanahi M. Recovering the mechanical properties of denatured intervertebral discs through Platelet-Rich Plasma therapy. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2018; 2015:933-6. [PMID: 26736416 DOI: 10.1109/embc.2015.7318516] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Degenerative disc disease is one of the most common causes of low back pain instigating huge socioeconomic costs and posing an immense burden on healthcare systems worldwide. New therapeutic approaches to damaged intervertebral discs are therefore of great interest. Platelet-Rich Plasma (PRP) has been proposed for the repair and regeneration of degenerated discs, but there remains a knowledge gap regarding its effectiveness and influence on disc material properties. The objective of this study was to investigate and quantify the material properties of intact, denatured, and PRP treated discs. A systematic methodology was established in the process, where ex-vivo experiments were conducted and material properties were extracted using an inverse finite element approach. The results showed that PRP is able to recover the mechanical properties of denatured discs, thereby providing a promising effective therapeutic modality.
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15
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Biomechanical response of intact, degenerated and repaired intervertebral discs under impact loading – Ex-vivo and In-Silico investigation. J Biomech 2018; 70:26-32. [DOI: 10.1016/j.jbiomech.2018.01.026] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 01/09/2018] [Accepted: 01/14/2018] [Indexed: 01/30/2023]
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16
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Nikkhoo M, Wang JL, Abdollahi M, Hsu YC, Parnianpour M, Khalaf K. A regenerative approach towards recovering the mechanical properties of degenerated intervertebral discs: Genipin and platelet-rich plasma therapies. Proc Inst Mech Eng H 2016; 231:127-137. [PMID: 28019241 DOI: 10.1177/0954411916681597] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Degenerative disc disease, associated with discrete structural changes in the peripheral annulus and vertebral endplate, is one of the most common pathological triggers of acute and chronic low back pain, significantly depreciating an individual's quality of life and instigating huge socioeconomic costs. Novel emerging therapeutic techniques are hence of great interest to both research and clinical communities alike. Exogenous crosslinking, such as Genipin, and platelet-rich plasma therapies have been recently demonstrated encouraging results for the repair and regeneration of degenerated discs, but there remains a knowledge gap regarding the quantitative degree of effectiveness and particular influence on the mechanical properties of the disc. This study aimed to investigate and quantify the material properties of intact (N = 8), trypsin-denatured (N = 8), Genipin-treated (N = 8), and platelet-rich plasma-treated (N = 8) discs in 32 porcine thoracic motion segments. A poroelastic finite element model was used to describe the mechanical properties during different treatments, while a meta-model analytical approach was used in combination with ex vivo experiments to extract the poroelastic material properties. The results revealed that both Genipin and platelet-rich plasma are able to recover the mechanical properties of denatured discs, thereby affording promising therapeutic modalities. However, platelet-rich plasma-treated discs fared slightly, but not significantly, better than Genipin in terms of recovering the glycosaminoglycans content, an essential building block for healthy discs. In addition to investigating these particular degenerative disc disease therapies, this study provides a systematic methodology for quantifying the detailed poroelastic mechanical properties of intervertebral disc.
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Affiliation(s)
- Mohammad Nikkhoo
- 1 Department of Biomedical Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
| | - Jaw-Lin Wang
- 2 Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University, Taipei, Taiwan, ROC
| | - Masoud Abdollahi
- 3 Laboratory of Wearable Technologies & Neuromusculoskeletal Research, Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran
| | - Yu-Chun Hsu
- 2 Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University, Taipei, Taiwan, ROC
| | - Mohamad Parnianpour
- 3 Laboratory of Wearable Technologies & Neuromusculoskeletal Research, Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran
| | - Kinda Khalaf
- 4 Department of Biomedical Engineering, Khalifa University of Science, Technology and Research, Abu Dhabi, UAE
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Thornton JS, Vinther A, Wilson F, Lebrun CM, Wilkinson M, Di Ciacca SR, Orlando K, Smoljanovic T. Rowing Injuries: An Updated Review. Sports Med 2016; 47:641-661. [DOI: 10.1007/s40279-016-0613-y] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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18
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Żak M, Pezowicz C. Analysis of the impact of the course of hydration on the mechanical properties of the annulus fibrosus of the intervertebral disc. EUROPEAN SPINE JOURNAL : OFFICIAL PUBLICATION OF THE EUROPEAN SPINE SOCIETY, THE EUROPEAN SPINAL DEFORMITY SOCIETY, AND THE EUROPEAN SECTION OF THE CERVICAL SPINE RESEARCH SOCIETY 2016; 25:2681-90. [DOI: 10.1007/s00586-016-4704-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Revised: 07/05/2016] [Accepted: 07/10/2016] [Indexed: 10/21/2022]
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Barthelemy VMP, van Rijsbergen MM, Wilson W, Huyghe JM, van Rietbergen B, Ito K. A computational spinal motion segment model incorporating a matrix composition-based model of the intervertebral disc. J Mech Behav Biomed Mater 2015; 54:194-204. [PMID: 26469631 DOI: 10.1016/j.jmbbm.2015.09.028] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 09/10/2015] [Accepted: 09/23/2015] [Indexed: 01/08/2023]
Abstract
The extracellular matrix of the intervertebral disc is subjected to changes with age and degeneration, affecting the biomechanical behaviour of the spine. In this study, a finite element model of a generic spinal motion segment that links spinal biomechanics and intervertebral disc biochemical composition was developed. The local mechanical properties of the tissue were described by the local matrix composition, i.e. fixed charge density, amount of water and collagen and their organisation. The constitutive properties of the biochemical constituents were determined by fitting numerical responses to experimental measurements derived from literature. This general multi-scale model of the disc provides the possibility to evaluate the relation between local disc biochemical composition and spinal biomechanics.
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Affiliation(s)
- V M P Barthelemy
- Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - M M van Rijsbergen
- Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - W Wilson
- Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - J M Huyghe
- Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - B van Rietbergen
- Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
| | - K Ito
- Orthopaedic Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
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Fan R, Gong H, Qiu S, Zhang X, Fang J, Zhu D. Effects of resting modes on human lumbar spines with different levels of degenerated intervertebral discs: a finite element investigation. BMC Musculoskelet Disord 2015; 16:221. [PMID: 26300114 PMCID: PMC4546817 DOI: 10.1186/s12891-015-0686-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Accepted: 08/14/2015] [Indexed: 12/29/2022] Open
Abstract
BACKGROUND The negative effect of long-term working load on lumbar is widely known. However, insertion of different resting modes on long-term working load, and its effects on the lumbar spine is rarely studied. The purpose of this study was to investigate the biomechanical responses of lumbar spine with different levels of degenerated intervertebral discs under different working-resting modes. METHODS Four poroelastic finite element models of lumbar spinal segments L2-L3 with different grades of disc degeneration were developed. Four different loading conditions represented four different resting frequencies, namely, no rest, one-time long rest, three-time moderate rests, and five-time short rests, on the condition that the total resting time was the same except in the no rest mode. Loading amplitudes of diurnal activities included 100 N, 300 N, and 500 N. RESULTS With increasing resting frequency, the axial effective stress and fluid loss decreased, whereas the pore pressure and radial displacement increased. Under different resting frequencies, the changing rate of each biomechanical parameter was different. CONCLUSIONS Under a situation of fixed total resting time, high resting frequency was advisable. If sufficient resting frequency was unavailable for healthy people as well as patients with mildly and moderately degenerated intervertebral discs, they could similarly benefit from relatively less resting frequencies. However, one-time rest will not be useful in cases where intervertebral discs were seriously degenerated. Reasonable working-resting modes for different degrees of disc degeneration, which could assist patients achieve a better restoration, were provided in this study.
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Affiliation(s)
- Ruoxun Fan
- Department of Engineering Mechanics, Nanling Campus, Jilin University, Changchun, 130025, P. R. China.
| | - He Gong
- Department of Engineering Mechanics, Nanling Campus, Jilin University, Changchun, 130025, P. R. China.
| | - Sen Qiu
- State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun, 130025, P. R. China.
| | - Xianbin Zhang
- Department of Engineering Mechanics, Nanling Campus, Jilin University, Changchun, 130025, P. R. China.
| | - Juan Fang
- Department of Engineering Mechanics, Nanling Campus, Jilin University, Changchun, 130025, P. R. China.
| | - Dong Zhu
- Department of Orthopedic Surgery, No. 1 Hospital of Jilin University, Changchun, 130025, People's Republic of China.
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Nikkhoo M, Khalaf K, Kuo YW, Hsu YC, Haghpanahi M, Parnianpour M, Wang JL. Effect of Degeneration on Fluid-Solid Interaction within Intervertebral Disk Under Cyclic Loading - A Meta-Model Analysis of Finite Element Simulations. Front Bioeng Biotechnol 2015; 3:4. [PMID: 25674562 PMCID: PMC4309208 DOI: 10.3389/fbioe.2015.00004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Accepted: 01/07/2015] [Indexed: 11/13/2022] Open
Abstract
The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid-fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid-solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid-fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk.
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Affiliation(s)
- Mohammad Nikkhoo
- Department of Biomedical Engineering, Science and Research Branch, Islamic Azad University , Tehran , Iran ; Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University , Taipei , Taiwan
| | - Kinda Khalaf
- Department of Biomedical Engineering, Khalifa University of Science, Technology and Research , Abu Dhabi , UAE
| | - Ya-Wen Kuo
- Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University , Taipei , Taiwan
| | - Yu-Chun Hsu
- Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University , Taipei , Taiwan
| | - Mohammad Haghpanahi
- School of Mechanical Engineering, Iran University of Science and Technology , Tehran , Iran
| | - Mohamad Parnianpour
- Department of Industrial and Manufacturing, University of Wisconsin , Milwaukee, WI , USA
| | - Jaw-Lin Wang
- Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University , Taipei , Taiwan
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22
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Castro APG, Wilson W, Huyghe JM, Ito K, Alves JL. Intervertebral disc creep behavior assessment through an open source finite element solver. J Biomech 2013; 47:297-301. [PMID: 24210477 DOI: 10.1016/j.jbiomech.2013.10.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Revised: 10/09/2013] [Accepted: 10/12/2013] [Indexed: 11/25/2022]
Abstract
Degenerative Disc Disease (DDD) is one of the largest health problems faced worldwide, based on lost working time and associated costs. By means of this motivation, this work aims to evaluate a biomimetic Finite Element (FE) model of the Intervertebral Disc (IVD). Recent studies have emphasized the importance of an accurate biomechanical modeling of the IVD, as it is a highly complex multiphasic medium. Poroelastic models of the disc are mostly implemented in commercial finite element packages with limited access to the algorithms. Therefore, a novel poroelastic formulation implemented on a home-developed open source FE solver is briefly addressed throughout this paper. The combination of this formulation with biphasic osmotic swelling behavior is also taken into account. Numerical simulations were devoted to the analysis of the non-degenerated human lumbar IVD time-dependent behavior. The results of the tests performed for creep assessment were inside the scope of the experimental data, with a remarkable improvement of the numerical accuracy when compared with previously published results obtained with ABAQUS(®). In brief, this in-development open-source FE solver was validated with literature experimental data and aims to be a valuable tool to study the IVD biomechanics and DDD mechanisms.
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Affiliation(s)
- A P G Castro
- Center for Mechanical and Materials Technologies (CT2M), University of Minho Campus of Azurem, 4800-058 Guimaraes, Portugal.
| | - W Wilson
- Biomedical Engineering Department, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
| | - J M Huyghe
- Biomedical Engineering Department, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
| | - K Ito
- Biomedical Engineering Department, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
| | - J L Alves
- Center for Mechanical and Materials Technologies (CT2M), University of Minho Campus of Azurem, 4800-058 Guimaraes, Portugal.
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Nikkhoo M, Hsu YC, Haghpanahi M, Parnianpour M, Wang JL. A meta-model analysis of a finite element simulation for defining poroelastic properties of intervertebral discs. Proc Inst Mech Eng H 2013; 227:672-82. [PMID: 23636748 DOI: 10.1177/0954411913480668] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Finite element analysis is an effective tool to evaluate the material properties of living tissue. For an interactive optimization procedure, the finite element analysis usually needs many simulations to reach a reasonable solution. The meta-model analysis of finite element simulation can be used to reduce the computation of a structure with complex geometry or a material with composite constitutive equations. The intervertebral disc is a complex, heterogeneous, and hydrated porous structure. A poroelastic finite element model can be used to observe the fluid transferring, pressure deviation, and other properties within the disc. Defining reasonable poroelastic material properties of the anulus fibrosus and nucleus pulposus is critical for the quality of the simulation. We developed a material property updating protocol, which is basically a fitting algorithm consisted of finite element simulations and a quadratic response surface regression. This protocol was used to find the material properties, such as the hydraulic permeability, elastic modulus, and Poisson's ratio, of intact and degenerated porcine discs. The results showed that the in vitro disc experimental deformations were well fitted with limited finite element simulations and a quadratic response surface regression. The comparison of material properties of intact and degenerated discs showed that the hydraulic permeability significantly decreased but Poisson's ratio significantly increased for the degenerated discs. This study shows that the developed protocol is efficient and effective in defining material properties of a complex structure such as the intervertebral disc.
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Affiliation(s)
- Mohammad Nikkhoo
- School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran
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Nikkhoo M, Haghpanahi M, Parnianpour M, Wang JL. DYNAMIC RESPONSES OF INTERVERTEBRAL DISC DURING STATIC CREEP AND DYNAMIC CYCLIC LOADING: A PARAMETRIC POROELASTIC FINITE ELEMENT ANALYSIS. BIOMEDICAL ENGINEERING: APPLICATIONS, BASIS AND COMMUNICATIONS 2013. [DOI: 10.4015/s1016237213500130] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Low back pain is a common reason for activity limitation in people younger than 45 years old, and was proved to be associated with heavy physical works, repetitive lifting, impact, stationary work postures and vibrations. The study of load transferring and the loading condition encountered in spinal column can be simulated by finite element models. The intervertebral disc is a structure composed of a porous material. Many physical models were developed to simulate this phenomenon. The confounding effects of poroelastic properties and loading conditions on disc mechanical responses are, nevertheless, not cleared yet. The objective of this study was to develop an axisymmetric poroelastic finite element model of intervertebral disc and use it to investigate the confounding effect of material properties and loading conditions on the disc deformation and pore pressure. An axisymmetric poroelastic model of human lumbar L4–L5 motion segment was developed. The model was validated by comparing the height loss and intradiscal pressure of the L4–L5 intervertebral disc with in vitro cadaveric studies. The effect of permeability, void ratio, elastic modulus, and Poisson's ratio on disc height and pore pressure was investigated for the following three loading conditions: (1) 1334 N creep loading, (2) peak-to-peak, 1000-to-1600 N, 1 Hz cyclic loading, and (3) same loading magnitude, but at 5 Hz loading frequency. The disc height loss and pore pressure of the three loading conditions were analyzed. The predictions of the disc height loss and intradiscal pressure of the current FE model are well comparable with the results of in vitro cadaveric studies. After model validation, the parametric study of disc poroelastic properties on the disc mechanical responses shows that the increase of permeability and void ratio increases the disc height loss and decreases the pore pressure, and these effects are sensitive to external loading frequency. Higher elastic modulus reduces the disc deformation and the pore pressure, but this reduction is not sensitive to the loading frequency. The effect of Poisson's ratio on disc height loss and pore pressure is negligible. In conclusion, the hydraulic permeability describes the fluid flow capability within tissue matrix which has a higher sensitivity on the saturation time for disc deformation and pore pressure. Void ratio directly affects the amount of mobile water within disc and changes time-dependent response of disc. Increase in loading frequency reduces time for fluid inflow and outflow, which fades out the role of permeability and void ratio. Values of elastic modulus and Poisson's ratio, which demonstrates stiffness and bulging capacity, respectively, do not affect the overall dynamic response of disc.
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Affiliation(s)
- Mohammad Nikkhoo
- School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran
- Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University, Taipei, Taiwan
| | - Mohammad Haghpanahi
- School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran
| | - Mohamad Parnianpour
- School of Mechanical Engineering, Sharif University of Technology, Tehran, Iran
| | - Jaw-Lin Wang
- Institute of Biomedical Engineering, College of Medicine and Engineering, National Taiwan University, Taipei, Taiwan
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Schmidt H, Reitmaier S. Is the ovine intervertebral disc a small human one? A finite element model study. J Mech Behav Biomed Mater 2012; 17:229-41. [PMID: 23127644 DOI: 10.1016/j.jmbbm.2012.09.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2012] [Revised: 09/03/2012] [Accepted: 09/10/2012] [Indexed: 11/27/2022]
Abstract
The sheep is one of the most frequently used animal models for experimental intervertebral disc research questions. Although there are large differences in size between human and ovine discs, recent in vivo and in vitro studies indicate similarities in the internal disc stresses. The present finite element model study, therefore, intended to detect the parameters that, despite the different geometry, ensure mechanical comparability between both species. At first, a finite element model of the human L4-L5 lumbar intervertebral disc was developed. The predicted displacement and nucleus pressure response were validated with experimental in vivo and in vitro data. Starting with adapting the model geometry from the human to the ovine disc, several material and biochemical parameters, which might contribute to the preservation of the mechanical disc response across both species, were successively adapted to ovine properties. Replacing the geometry yielded a substantially higher disc stiffness and lower nucleus pressure compared to in vitro measurements performed on ovine discs. Additional reduction of annulus and nucleus elasticity led to an improved correlation between model predictions and measurements. Changes in the glycosaminoglycan content and endplate permeability improved the predicted pressure, but only slightly affected the displacement response. Only the combination of all parameters resulted in a good agreement between the predictions and measurements. This study demonstrated that there are profound differences between model predictions and in vitro results if an ovine simulation is run with human material properties. However, once the species-specific material properties are included, the predictions fit the in vitro results. Therefore, it seems that the human and ovine disc is functionally adapted to produce similar internal stresses, despite the large variation in geometry.
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Affiliation(s)
- Hendrik Schmidt
- Julius Wolff Institut Charité-Universitätsmedizin Berlin, CVK, Institutsgebäude Süd/Südstraße 2, Augustenburger Platz 1, 13353 Berlin, Germany.
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Abstract
STUDY DESIGN An in vitro biomechanics investigation exposing porcine functional spinal units (FSUs) to submaximal cyclic or static compressive forces while in a flexed, neutral, or extended posture. OBJECTIVE To investigate the combined effect of cyclically applied compressive force (e.g., vibration) and postural deviation on intervertebral joint mechanics. SUMMARY OF BACKGROUND DATA Independently, prolonged vibration exposure and non-neutral postures are known risk factors for development of low back pain and injury. However, there is limited basic scientific evidence to explain how the risk of low back injury from vibration exposure is modified by other mechanical factors. This work examined the influence of static postural deviation on vertebral joint height loss and compressive stiffness under cyclically applied compressive force. METHODS Forty-eight FSUs, consisting of 2 adjacent vertebrae, ligaments, and the intervening intervertebral disc were included in the study. Each specimen was randomized to 1 of 3 experimental posture conditions (neutral, flexed, or extended) and assigned to 1 of 2 loading protocols, consisting of (1) cyclic (1500 ± 1200 N applied at 5 Hz using a sinusoidal waveform, resulting in 0.2 g rms acceleration) or (2) 1500 N of static compressive force. RESULTS.: As expected, FSU height loss followed a typical first-order response in both the static and cyclic loading protocols, with the majority (~50%) of the loss occurring in the first 20 minutes of testing. A significant interaction between posture and loading protocol (P < 0.001) was noted in the magnitude of FSU height loss. Subsequent analysis of simple effects revealed significant differences between cyclic and static loading protocols in both a neutral (P = 0.016) and a flexed posture (P < 0.0001). No significant differences (P = 0.320) were noted between pre/postmeasurements of FSU compressive stiffness. CONCLUSION Posture is an important mechanical factor to consider when assessing the risk of injury from cyclic loading to the lumbar spine.
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Heuer F, Schmidt H, Käfer W, Graf N, Wilke HJ. Posterior motion preserving implants evaluated by means of intervertebral disc bulging and annular fiber strains. Clin Biomech (Bristol, Avon) 2012; 27:218-25. [PMID: 21983522 DOI: 10.1016/j.clinbiomech.2011.09.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 09/13/2011] [Accepted: 09/13/2011] [Indexed: 02/07/2023]
Abstract
BACKGROUND The aims of motion preserving implants are to ensure sufficient stability to the spine, to release facet joints by also allowing a physiological loading to the intervertebral disc. The aim of this study was to assess disc load contribution by means of annular fiber strains and disc bulging of intact and stiffened segments. This was compared to the segments treated with various motion preserving implants. METHODS A laser scanning device was used to obtain three-dimensional disc bulging and annular fiber strains of six lumbar intervertebral discs (L2-3). Specimens were loaded with 500N or 7.5Nm moments in a spine tester. Each specimen was treated with four different implants; DSS™, internal fixator, Coflex™, and TOPS™. FINDINGS In axial compression, all implants performed in a similar way. In flexion, the Coflex decreased range of motion by 13%, whereas bulging and fiber strains were similar to intact. The DSS stabilized segments by 54% compared to intact. TOPS showed a slight decrease in fiber strains (5%) with a range of motion similar to intact. The rigid fixator allowed strains up to 2%. In lateral bending, TOPS yielded range of motion values similar to intact, but maximum fiber strains doubled from 6.5% (intact) to 13.8%. Coflex showed range of motion, bulging and strain values similar to intact. The DSS and the rigid fixator reduced these values. The implants produced only minor changes in axial rotation. INTERPRETATION This study introduces an in vitro method, which was employed to evaluate spinal implants other than standard biomechanical methods. We could demonstrate that dynamic stabilization methods are able to keep fiber strains and disc bulging in a physiological range.
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Affiliation(s)
- Frank Heuer
- Institute of Orthopaedic Research and Biomechanics, Director Prof. Lutz Claes, University of Ulm, Helmholtzstrasse 14, Ulm, Germany
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Malandrino A, Noailly J, Lacroix D. Regional annulus fibre orientations used as a tool for the calibration of lumbar intervertebral disc finite element models. Comput Methods Biomech Biomed Engin 2012; 16:923-8. [PMID: 22224724 DOI: 10.1080/10255842.2011.644539] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Abstract
The collagen network of the annulus fibrosus largely controls the functional biomechanics of the lumbar intervertebral discs (IVDs). Quantitative anatomical examinations have shown bundle orientation patterns, possibly coming from regional adaptations of the annulus mechanics. This study aimed to show that the regional differences in annulus mechanical behaviour could be reproduced by considering only fibre orientation changes. Using the finite element method, a lumbar annulus was modelled as a poro-hyperelastic material in which fibres were represented by a direction-dependent strain energy density term. Fibre orientations were calibrated to reproduce the annulus tensile behaviours measured for four different regions: posterior outer, anterior outer, posterior inner and anterior inner. The back-calculated fibre angles and regional patterns as well as the global disc behaviour were comparable with anatomical descriptions reported in the literature. It was concluded that annulus fibre variations might be an effective tool to calibrate lumbar spine IVD and segment models.
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Massey CJ, van Donkelaar CC, Vresilovic E, Zavaliangos A, Marcolongo M. Effects of aging and degeneration on the human intervertebral disc during the diurnal cycle: a finite element study. J Orthop Res 2012; 30:122-8. [PMID: 21710607 DOI: 10.1002/jor.21475] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Accepted: 05/16/2011] [Indexed: 02/04/2023]
Abstract
A significant biochemical change that takes place in intervertebral disc degeneration is the loss of proteoglycans in the nucleus pulposus. Proteoglycans attract fluid, which works to reduce mechanical stresses in the solid matrix of the nucleus and provide a hydrostatic pressure to the annulus fibrosus, whose fibrous nature accommodates this stress. Our goals are to develop an osmo-poroelastic finite element model to study the relationship between proteoglycan content and the stress distribution within the disc and to analyze the effects of degeneration on the disc's diurnal mechanical response. Stress in the annulus increased with degeneration from ∼0.2 to 0.4 MPa, and an increase occurred in the center of the nucleus from 1.2 to 1.6 MPa. The osmotic pressure in the central nucleus region decreased the most with degeneration, from ∼0.42 to ∼0.1 MPa in a severely dehydrated disc. A 3% decrease in diurnal fluid lost with degeneration equated to ∼21% decrease in fluid exchange, and hence a decrease in nutrients that require convection to enter the disc. We quantified the increases in internal stresses in the nucleus and annulus throughout the various stages of degeneration, suggesting that these changes lead to further remodeling of the tissue.
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Affiliation(s)
- Christopher J Massey
- Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA, USA
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Boustani HN, Zander T, Disch AC, Rohlmann A. Pedicle-screw-based dynamic implants may increase posterior intervertebral disc bulging during flexion. ACTA ACUST UNITED AC 2011; 56:327-31. [PMID: 22103650 DOI: 10.1515/bmt.2011.023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Abstract Posterior disc bulging may lead to nerve root compression and radicular pain, and in extreme cases to a local pressure on the dural sac and thus to back pain. Compared to when standing, posterior disc bulging is increased during extension and decreased during flexion, in an uninstrumented spine. The aim of this study was to determine the effect of a pedicle-screw-based dynamic implant on posterior disc bulging. A finite element model of the lumbosacral spine was used to calculate posterior disc bulging before and after implantation of a dynamic implant for different loading cases. The elastic modulus of the longitudinal rod was varied, and the influence of distraction of the bridged segment on disc bulging was also determined. In addition, the centre of rotation (CoR) was determined. Due to a dynamic implant, the magnitude of posterior disc bulging was reduced compared to that for "standing without an implant" during extension, lateral bending, and axial rotation. During flexion, however, disc bulging was usually increased. With increasing stiffness of the dynamic implant, the CoR moved towards the longitudinal rod. This posterior shift of the CoR led to a compression of the entire intervertebral disc during flexion and thus to an increase of disc bulging.
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Affiliation(s)
- Hadi N Boustani
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Germany
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Malandrino A, Noailly J, Lacroix D. The effect of sustained compression on oxygen metabolic transport in the intervertebral disc decreases with degenerative changes. PLoS Comput Biol 2011; 7:e1002112. [PMID: 21829341 PMCID: PMC3150290 DOI: 10.1371/journal.pcbi.1002112] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Accepted: 05/19/2011] [Indexed: 11/19/2022] Open
Abstract
Intervertebral disc metabolic transport is essential to the functional spine and provides the cells with the nutrients necessary to tissue maintenance. Disc degenerative changes alter the tissue mechanics, but interactions between mechanical loading and disc transport are still an open issue. A poromechanical finite element model of the human disc was coupled with oxygen and lactate transport models. Deformations and fluid flow were linked to transport predictions by including strain-dependent diffusion and advection. The two solute transport models were also coupled to account for cell metabolism. With this approach, the relevance of metabolic and mechano-transport couplings were assessed in the healthy disc under loading-recovery daily compression. Disc height, cell density and material degenerative changes were parametrically simulated to study their influence on the calculated solute concentrations. The effects of load frequency and amplitude were also studied in the healthy disc by considering short periods of cyclic compression. Results indicate that external loads influence the oxygen and lactate regional distributions within the disc when large volume changes modify diffusion distances and diffusivities, especially when healthy disc properties are simulated. Advection was negligible under both sustained and cyclic compression. Simulating degeneration, mechanical changes inhibited the mechanical effect on transport while disc height, fluid content, nucleus pressure and overall cell density reductions affected significantly transport predictions. For the healthy disc, nutrient concentration patterns depended mostly on the time of sustained compression and recovery. The relevant effect of cell density on the metabolic transport indicates the disturbance of cell number as a possible onset for disc degeneration via alteration of the metabolic balance. Results also suggest that healthy disc properties have a positive effect of loading on metabolic transport. Such relation, relevant to the maintenance of the tissue functional composition, would therefore link disc function with disc nutrition.
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Affiliation(s)
| | - Jérôme Noailly
- Institute for Bioengineering of Catalonia, Barcelona, Spain
| | - Damien Lacroix
- Institute for Bioengineering of Catalonia, Barcelona, Spain
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3D non-affine finite strains measured in isolated bovine annulus fibrosus tissue samples. Biomech Model Mechanobiol 2011; 11:161-70. [PMID: 21451947 DOI: 10.1007/s10237-011-0300-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2010] [Accepted: 03/04/2011] [Indexed: 10/18/2022]
Abstract
Understanding of the mechanics of disc tissue calls for measurement of strains in physiological conditions. Because the intervertebral disc is gripped between two vertebrae, the swelling is constrained in vivo, resulting in a intradiscal pressure of 0.1-0.2 MPa in supine position. The excision of isolated disc tissue samples results often in non-physiological swelling. The purpose of the present study is to measure 3D finite strains in isolated bovine disc tissue specimens under physiological osmolarity and pressure, particularly around discontinuities of the collagen network. The collagen is stained by means of CNA35 probe, and the (dead) cells are stained by means of propidium iodide. The tissue is observed under confocal microscopy, under an externally applied pressure generated by a PEG solution. The 3D finite strains are obtained through correlation of the texture of the 3D images. The correlation technique yields principal strains in all areas except within collagen-free areas. The deformation is strongly non-affine. Especially around discontinuities, the strain field is non-homogeneous. Macroscopic strains as computed from finite element analysis of whole discs are insufficient to predict microstrains around clefts or cells. Because of the small number of specimens, the present results should be considered preliminary.
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Adams MA, Stefanakis M, Dolan P. Healing of a painful intervertebral disc should not be confused with reversing disc degeneration: implications for physical therapies for discogenic back pain. Clin Biomech (Bristol, Avon) 2010; 25:961-71. [PMID: 20739107 DOI: 10.1016/j.clinbiomech.2010.07.016] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Revised: 07/23/2010] [Accepted: 07/27/2010] [Indexed: 02/07/2023]
Abstract
BACKGROUND Much is known about intervertebral disc degeneration, but little effort has been made to relate this information to the clinical problem of discogenic back pain, and how it might be treated. METHODS We re-interpret the scientific literature in order to provide a rationale for physical therapy treatments for discogenic back pain. INTERPRETATION Intervertebral discs deteriorate over many years, from the nucleus outwards, to an extent that is influenced by genetic inheritance and metabolite transport. Age-related deterioration can be accelerated by physical disruption, which leads to disc "degeneration" or prolapse. Degeneration most often affects the lower lumbar discs, which are loaded most severely, and it is often painful because nerves in the peripheral anulus or vertebral endplate can be sensitised by inflammatory-like changes arising from contact with blood or displaced nucleus pulposus. Surgically-removed human discs show an active inflammatory process proceeding from the outside-in, and animal studies confirm that effective healing occurs only in the outer anulus and endplate, where cell density and metabolite transport are greatest. Healing of the disc periphery has the potential to relieve discogenic pain, by re-establishing a physical barrier between nucleus pulposus and nerves, and reducing inflammation. CONCLUSION Physical therapies should aim to promote healing in the disc periphery, by stimulating cells, boosting metabolite transport, and preventing adhesions and re-injury. Such an approach has the potential to accelerate pain relief in the disc periphery, even if it fails to reverse age-related degenerative changes in the nucleus.
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Affiliation(s)
- Michael A Adams
- Centre for Comparative and Clinical Anatomy, University of Bristol, Bristol, UK.
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Noailly J, Planell JA, Lacroix D. On the collagen criss-cross angles in the annuli fibrosi of lumbar spine finite element models. Biomech Model Mechanobiol 2010; 10:203-19. [DOI: 10.1007/s10237-010-0227-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2009] [Accepted: 05/17/2010] [Indexed: 11/28/2022]
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Hussain M, Gay RE, An KN. Reduction in Disk and Fiber Stresses by Axial Distraction is Higher in Cervical Disk With Fibers Oriented Toward the Vertical Rather Than Horizontal Plane: A Finite Element Model Analysis. J Manipulative Physiol Ther 2010; 33:252-60. [DOI: 10.1016/j.jmpt.2010.03.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Revised: 02/05/2010] [Accepted: 02/09/2010] [Indexed: 11/27/2022]
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Schroeder Y, Huyghe JM, van Donkelaar CC, Ito K. A biochemical/biophysical 3D FE intervertebral disc model. Biomech Model Mechanobiol 2010; 9:641-50. [PMID: 20229171 DOI: 10.1007/s10237-010-0203-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Accepted: 02/23/2010] [Indexed: 01/07/2023]
Abstract
Present research focuses on different strategies to preserve the degenerated disc. To assure long-term success of novel approaches, favorable mechanical conditions in the disc tissue are essential. To evaluate these, a model is required that can determine internal mechanical conditions which cannot be directly measured as a function of assessable biophysical characteristics. Therefore, the objective is to evaluate if constitutive and material laws acquired on isolated samples of nucleus and annulus tissue can be used directly in a whole-organ 3D FE model to describe intervertebral disc behavior. The 3D osmo-poro-visco-hyper-elastic disc (OVED) model describes disc behavior as a function of annulus and nucleus tissue biochemical composition, organization and specific constituent properties. The description of the 3D collagen network was enhanced to account for smaller fibril structures. Tissue mechanical behavior tests on isolated nucleus and annulus samples were simulated with models incorporating tissue composition to calculate the constituent parameter values. The obtained constitutive laws were incorporated into the whole-organ model. The overall behavior and disc properties of the model were corroborated against in vitro creep experiments of human L4/L5 discs. The OVED model simulated isolated tissue experiments on confined compression and uniaxial tensile test and whole-organ disc behavior. This was possible, provided that secondary fiber structures were accounted for. The fair agreement (radial bulge, axial creep deformation and intradiscal pressure) between model and experiment was obtained using constitutive properties that are the same for annulus and nucleus. Both tissue models differed in the 3D OVED model only by composition. The composition-based modeling presents the advantage of reducing the numbers of material parameters to a minimum and to use tissue composition directly as input. Hence, this approach provides the possibility to describe internal mechanical conditions of the disc as a function of assessable biophysical characteristics.
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Affiliation(s)
- Y Schroeder
- Department of Biomedical Engineering, Eindhoven University of Technology, The Netherlands
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Changes in Intervertebral Disk Dimensions After a Loading Task and the Relationship With Stature Change Measurements. Arch Phys Med Rehabil 2009; 90:1795-9. [DOI: 10.1016/j.apmr.2009.04.017] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Revised: 03/06/2009] [Accepted: 04/09/2009] [Indexed: 11/29/2022]
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Bulging of the inner and outer annulus during in vivo axial loading of normal and degenerated discs. ACTA ACUST UNITED AC 2009; 22:214-8. [PMID: 19412025 DOI: 10.1097/bsd.0b013e31816f68b5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
STUDY DESIGN Comparison of in vivo biomechanical outcomes between experimental and control group animals. OBJECTIVE To quantify the in vivo bulging response of the inner and outer annulus in animals with and without disc degeneration. SUMMARY OF BACKGROUND DATA Prior attempts to quantify the load-deformation response of the inner annulus have most often relied on in vitro preparations. Unfortunately, to visualize the inner annulus, these in vitro approaches rely on disc modifications that may result in nonphysiologic behaviors. In response to this problem, in vivo techniques were developed to quantify regional bulging of the inner and outer annulus during applied axial loading. METHODS Two groups of pigs were tested: a normal group and a group having disc degeneration that was induced surgically 3 months earlier. Eight adolescent pigs were evaluated and for each animal, a miniature servohydraulic actuator was attached to the third and fourth lumbar vertebrae to deliver a cyclic axial loading protocol (300 N, 1 Hz, 10 cycles) whereas regional deformations of the annulus were visualized ultrasonically via retroperitoneal access. RESULTS For the normal animals, image analysis demonstrated a significantly greater bulging of the inner annular region when compared with the outer annular region. In animals with disc degeneration, the inner and outer annular regions were equal in their bulging response, which ranged from 0 bulging to 37% greater than the average response of the normal animals. CONCLUSIONS This work supports prior in vitro studies that observed maximal disc bulging in the inner annulus and minimal bulging in the external annulus. Results for this in vivo study suggest that this normal bulging gradient is lost with degenerative disc disease. Compared with in vitro approaches, this new in vivo technique has the potential to demonstrate disc behavior in a variety of loading conditions and/or with a variety of induced disc pathologies.
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Prospective design delineation and subsequent in vitro evaluation of a new posterior dynamic stabilization system. Spine (Phila Pa 1976) 2009; 34:255-61. [PMID: 19179920 DOI: 10.1097/brs.0b013e3181920e9c] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN Finite element and in vitro study. OBJECTIVE Finite element calculations to delineate a dynamic fixator and confirmation with an in vitro experiment. SUMMARY AND BACKGROUND DATA In the last few years, there was a paradigm shift from rigid to dynamic fixation of spinal segments. However, some so-called dynamic implants like the Dynesys performed still stiffer than anticipated. The aim of this study was to optimize a dynamic stabilization system. METHODS The development steps of this implant design can be summarized in a development loop. First, a finite element model of an intact human L4-L5 segment was used to delineate implant stiffness parameters for the implant, in consideration of clinical concerns and safety aspects. These data were used in a second step, leading to the final implant design. This development process was completed with an appropriate in vitro experiment. The optimal axial and bending stiffness were computed to reduce the spinal motion by 30%. For the validation process, in vitro tests were performed on 6 human lumbar spinal segments L2-L3 with a median age of 52. The model and the specimens were loaded with pure unconstrained moments of 7.5 Nm in flexion, extension, lateral bending, and axial rotation. RESULTS This study demonstrated the advantages of employing a finite element model for the implant parameter delineation. It was possible to prospectively outline the needed stiffness parameters for a desired spinal range of motion achievement. CONCLUSION In summary, FEM may accelerate the development and the realization of a new implant design.
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Schmidt H, Heuer F, Wilke HJ. Which axial and bending stiffnesses of posterior implants are required to design a flexible lumbar stabilization system? J Biomech 2008; 42:48-54. [PMID: 19038390 DOI: 10.1016/j.jbiomech.2008.10.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Revised: 10/03/2008] [Accepted: 10/07/2008] [Indexed: 10/21/2022]
Abstract
Dynamic stabilization devices have been introduced to clinics as an alternative to rigid fixation. The stiffness of these devices varies widely, whereas the optimal stiffness, achieving a predefined stabilization of the spine, is unknown. This study was focused on the determination of stiffness values for posterior stabilization devices achieving a flexible, semi-flexible or rigid connection between two vertebrae. An extensively validated finite element model of a lumbar spinal segment L4-5 with an implanted posterior fixation device was used in this study. The model was exposed to pure moments of 7.5 and 20Nm around the three principal anatomical directions, simulating flexion, extension, lateral bending and axial rotation. In parametrical studies, the influence of the axial and bending fixator stiffness on the spinal range of motion was investigated. In order to examine the validity of the computed results, an in-vitro study was carried out. In this, the influence of two posterior stabilization devices (DSS and rigidly internal fixator) on the segmental stabilization was investigated. The finite element (FE)-model predicted that each load direction caused a pairing of stiffness relations between axial and bending stiffness. In flexion and extension, however, the bending stiffness had a neglectable effect on the segmental stabilization, compared to the axial stiffness. In contrast, lateral bending and axial rotation were influenced by both stiffness parameters. Except in axial rotation, the model predictions were in a good agreement with the determined in-vitro data. In axial rotation, the FE-model predicted a stiffer segmental behavior than it was determined in the in-vitro study. It is usually expected that high stiffness values are required for a posterior stabilization device to stiffen a spinal segment. We found that already small stiffness values were sufficient to cause a stiffening. Using these data, it may possible to develop implants for certain clinical indications.
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Affiliation(s)
- Hendrik Schmidt
- Institute of Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany
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41
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A method to obtain surface strains of soft tissues using a laser scanning device. J Biomech 2008; 41:2402-10. [DOI: 10.1016/j.jbiomech.2008.05.031] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2007] [Revised: 05/23/2008] [Accepted: 05/24/2008] [Indexed: 11/23/2022]
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Heuer F, Schmidt H, Claes L, Wilke HJ. A new laser scanning technique for imaging intervertebral disc displacement and its application to modeling nucleotomy. Clin Biomech (Bristol, Avon) 2008; 23:260-9. [PMID: 18022738 DOI: 10.1016/j.clinbiomech.2007.10.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 10/01/2007] [Accepted: 10/02/2007] [Indexed: 02/07/2023]
Abstract
BACKGROUND Nucleotomy is a standard procedure for treating disc prolapse. It can reduce intervertebral disc height, flattening and displacing the disc, which could lead to a painful narrowing of the foramina due to nerve root compression. The purpose of this study was to investigate the disc displacement of a complete spinal segment with and without nucleotomy. We hypothesized that a nucleotomy under a certain load combination might amplify disc displacement. METHODS A laser scanner was developed for recording three-dimensional disc displacement of six loaded L4-5 specimens for three conditions: intact, disc with vertebral bodies and subsequent nucleotomy. Specimens were exposed to pure moments of 7.5 N m in the three principal anatomical directions. Disc displacement was obtained at maximal deflection. A finite element model was validated and subsequently utilized to determine disc displacement. The task of the finite element model was to provide supplemental data for the posterolateral region, which could not be measured from intact specimens. FINDINGS Disc displacement measurements of intact specimens were limited to the anterior part of discs, whereas the finite element model was able to provide the missing data of the dorsal disc region. The simulation of load combinations showed that the highest disc displacement was 1.9 mm at the lateral or posterolateral region. The nucleotomy increased the disc displacement up to 2.1mm, whereas the displacement zenith migrated posterolaterally. INTERPRETATION These results could be a possible explanation for disadvantages of nucleotomy as a treatment. With the methodology presented here, we would be able to assess the performance of nucleus implants by determining the disc displacement map. This could also give us appropriate information of the annular deformation, which is needed for the development of motion preserving implants.
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Affiliation(s)
- Frank Heuer
- Institute of Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstr. 14, 89081 Ulm, Germany
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Schmidt H, Heuer F, Claes L, Wilke HJ. The relation between the instantaneous center of rotation and facet joint forces - A finite element analysis. Clin Biomech (Bristol, Avon) 2008; 23:270-8. [PMID: 17997207 DOI: 10.1016/j.clinbiomech.2007.10.001] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2007] [Revised: 09/19/2007] [Accepted: 10/01/2007] [Indexed: 02/07/2023]
Abstract
BACKGROUND The instantaneous center of rotation in a functional spinal unit is an indicator for mechanical disorders and is relevant for the development of motion preserving techniques. In addition to the intervertebral disc, the facet joints also play a major role for load transmission through the spine, providing stability to it. The relationship between the rotation center and facet joint forces is not fully understood, since previous studies have separated both; spinal motion and facet forces. METHODS A finite element model of a L4-5 lumbar spinal segment was exposed to an axial compression preload of 500 N. Pure unconstrained moments of 7.5 Nm were additionally applied in the three anatomical main planes. The instantaneous center of rotation and the facet joint forces were investigated. FINDINGS For small moments, the center of rotation was found to be almost in the center of the disc, no matter what motion direction. With an increasing flexion moment, the center of rotation moved anteriorly. The facet joints remained unloaded in flexion. With proceeding extension movement, the center of rotation moved posteriorly. The facet forces increased up to 50 N. In lateral bending, with increasing moment the center of rotation migrated posteriorly in the ipsilateral side of the disc. The forces in the facet joints rose to 36 N. In axial rotation, the center of rotation migrated towards the compressed facet joint with increasing moment. Axial rotation yielded the maximum facet forces with 105 N. INTERPRETATION The determination of the rotation center is highly sensible against measurement resolution obtained during in vivo and in vitro studies. This finite element method can be used to complement the knowledge of the rotation center location from former experimental findings.
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Affiliation(s)
- Hendrik Schmidt
- Institute of Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.
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Heuer F, Schmidt H, Wilke HJ. The relation between intervertebral disc bulging and annular fiber associated strains for simple and complex loading. J Biomech 2008; 41:1086-94. [PMID: 18187139 DOI: 10.1016/j.jbiomech.2007.11.019] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 11/28/2007] [Accepted: 11/29/2007] [Indexed: 10/22/2022]
Abstract
Mechanical failure of the annulus fibrosus is mostly indicated by tears, fissures, protrusions or disc prolapses. Some of these annulus failures can be caused by a high intradiscal pressure. This has an effect on disc bulging. However, it is not fully understood how disc bulging is related to disc loading. Therefore, the aim of this study was to investigate the annular fiber strains and disc bulging under simple and complex spinal loads. A novel laser scanner was used to image surfaces of six L2-3 segments. Specimens were loaded with 500 N or 7.5 Nm in a spine tester while acquiring surface maps. Loading was applied in the three principal main directions and four combined directions. Disc bulging and tissue surface strains in annulus collagen fiber directions were computed. Two conditions were measured; intact and defect (vertebral body-disc-body units). Axial compression resulted in 2.7% fiber associated strains in intact segments and the defect increased strains up to 6.7%. Disc bulging increased from 0.7 mm to 0.87 mm. Flexion produced 7.2% fiber associated strains and 1.63 mm bulge going up to 17.5% and 2.21 mm after the defect. Highest fiber associated strains were found for the combination of axial rotation plus lateral bending with 24.6% and with a maximal bulging of 1.14 mm. It was found that there is no tight relationship between fiber associated strains and disc bulging. This was especially seen for the load combinations. Highest fiber associated strains were found to be located in small posterolateral regions. Fiber associated strains had a much higher magnitude than previously reported fiber associated strains. The results showed that combined loading is most likely to produce higher associated fiber strains compared to single axis loading.
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Affiliation(s)
- Frank Heuer
- Institute of Orthopaedic Research and Biomechanics, Director Prof. Lutz Claes, University of Ulm, Helmholtzstr. 14, 89081 Ulm, Germany
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45
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Stepwise reduction of functional spinal structures increase disc bulge and surface strains. J Biomech 2008; 41:1953-60. [DOI: 10.1016/j.jbiomech.2008.03.023] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2008] [Revised: 03/25/2008] [Accepted: 03/28/2008] [Indexed: 11/21/2022]
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