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Xu C, Xi Z, Fang Z, Zhang X, Wang N, Li J, Liu Y. Annulus Calibration Increases the Computational Accuracy of the Lumbar Finite Element Model. Global Spine J 2023; 13:2310-2318. [PMID: 35293827 PMCID: PMC10538312 DOI: 10.1177/21925682221081224] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
STUDY DESIGN Mechanical simulations. OBJECTIVE Inadequate calibration of annuli negatively affects the computational accuracy of finite element (FE) models. Specifically, the definition of annulus average radius (AR) does not have uniformity standards. Differences between the elastic moduli in the different layers and parts of the annulus were not fully calibrated when a linear elastic material is used to define its material properties. This study aims to optimize the computational accuracy of the FE model by calibrating the annulus. METHODS We calibrated the annulus AR and elastic modulus in our anterior-constructed lumbar model by eliminating the difference between the computed range of motion and that measured by in vitro studies under a flexion-extension loading condition. Multi-indicator validation was performed by comparing the computed indicators with those measured in in vitro studies. The computation time required for the different models has also been recorded to evaluate the computational efficiency. RESULTS The difference between computed and measured ROMs was less than 1% when the annulus AR and elastic modulus were calibrated. In the model validation process, all the indicators computed by the calibrated FE model were within ±1 standard deviation of the average values obtained from in vitro studies. The maximum difference between the computed and measured values was less than 10% under nearly all loading conditions. There is no apparent variation tendency for the computational time associated with different models. CONCLUSION The FE model with calibrated annulus AR and regional elastic modulus has higher computational accuracy and can be used in subsequent mechanical studies.
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Affiliation(s)
- Chen Xu
- Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, Shanghai, China
| | - Zhipeng Xi
- Department of Orthopedics, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing, China
| | - Zhongxin Fang
- Fluid and Power Machinery Key Laboratory of Ministry of Education, Xihua University, Chengdu, China
| | - Xiaoyu Zhang
- Department of Orthopedics, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing, China
| | - Nan Wang
- Department of Orthopedics, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing, China
| | - Jingchi Li
- Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, Shanghai, China
- Department of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, Luzhou, China
| | - Yang Liu
- Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, Shanghai, China
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Huang C, Liu Z, Wei Z, Fang Z, Xi Z, Cai P, Li J. Will the adjustment of insertional pedicle screw positions affect the risk of adjacent segment diseases biomechanically? An in-silico study. Front Surg 2023; 9:1004642. [PMID: 36713678 PMCID: PMC9877423 DOI: 10.3389/fsurg.2022.1004642] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Accepted: 09/20/2022] [Indexed: 01/13/2023] Open
Abstract
Background The fixation-induced biomechanical deterioration will increase the risk of adjacent segment diseases (ASD) after lumbar interbody fusion with Bilateral pedicle screw (BPS) fixation. The accurate adjustment of insertional pedicle screw positions is possible, and published studies have reported its mechanical effects. However, no studies clarified that adjusting insertional screw positions would affect the postoperative biomechanical environment and the risk of ASD. The objective of this study was to identify this issue and provide theoretical references for the optimization of insertional pedicle screw position selections. Methods The oblique lumbar interbody fusion fixed by BPS with different insertional positions has been simulated in the L4-L5 segment of our previously constructed and validated lumbosacral model. Biomechanical indicators related to ASD have been computed and recorded under flexion, extension, bending, and axial rotation loading conditions. Results The change of screw insertional positions has more apparent biomechanical effects on the cranial than the caudal segment. Positive collections can be observed between the reduction of the fixation length and the alleviation of motility compensation and stress concentration on facet cartilages. By contrast, no pronounced tendency of stress distribution on the intervertebral discs can be observed with the change of screw positions. Conclusions Reducing the fixation stiffness by adjusting the insertional screw positions could alleviate the biomechanical deterioration and be an effective method to reduce the risk of ASD caused by BPS.
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Affiliation(s)
- Chenyi Huang
- Department of Orthopedics, The Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University, Luzhou, China
| | - Zongchao Liu
- Department of Orthopedics, The Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University, Luzhou, China
| | - Zhangchao Wei
- Department of Orthopedics, The Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University, Luzhou, China
| | - Zhongxin Fang
- Fluid and Power Machinery Key Laboratory of Ministry of Education, Xihua University, Chengdu, China
| | - Zhipeng Xi
- Department of Spine Surgery, Jiangsu Province Hospital on Integration of Chinese and Western Medicine, Nanjing, China
| | - Ping Cai
- Department of Orthopedics, Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing, China,Correspondence: Jingchi Li Ping Cai
| | - Jingchi Li
- Department of Orthopedics, The Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University, Luzhou, China,Correspondence: Jingchi Li Ping Cai
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Li J, Zhang Z, Xie T, Song Z, Song Y, Zeng J. The preoperative Hounsfield unit value at the position of the future screw insertion is a better predictor of screw loosening than other methods. Eur Radiol 2023; 33:1526-1536. [PMID: 36241918 PMCID: PMC9935714 DOI: 10.1007/s00330-022-09157-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Revised: 08/11/2022] [Accepted: 09/09/2022] [Indexed: 11/04/2022]
Abstract
OBJECTIVE Screw loosening is a widely reported issue after spinal screw fixation and triggers several complications after lumbar interbody fusion. Osteoporosis is an essential risk factor for screw loosening. Hounsfield units (HU) value is a credible indicator during bone mineral density (BMD) evaluation. As compared with the general evaluation of BMD, we hypothesized that specific measurements of HU at the precise location of the future screw insertion may be a better predictor of screw loosening. METHODS Clinical data of 56 patients treated by oblique lumbar interbody fusion (OLIF) of the L4-L5 segments with an anterior lateral single rod (ALSR) screw fixation were reviewed in this study. Vertebral bodies with ≥ 1 mm width radiolucent zones around the screw were defined as screw loosening. HU in the insertional screw positions, the central transverse plane, and the average values of three and four planes were measured. Regression analyses identified independent risk factors for screw loosening separately. The area under the receiver operating characteristic curve (AUC) was computed to evaluate predictive performance. RESULTS The local HU values were significantly lower in the loosening group, regardless of the selected measuring methods. The AUC of screw loosening prediction was higher in the insertional screw positions' HU than other frequently used methods. CONCLUSIONS The HU value measured in the insertional screw position is a better predictor of ALSR screw loosening than other methods. The risk of screw loosening should be reduced by optimizing the trajectory of the screw based on the measurement of HU in preoperative CT. KEY POINTS • Osteoporosis is an essential risk factor for screw loosening, and Hounsfield units (HU) are a credible predictor during bone mineral density (BMD) evaluation. • The HU value measured in the insertional screw position is a better predictor of screw loosening than other frequently used HU measurement methods. • The risk of screw loosening might potentially be reduced by optimizing the trajectory of the screw based on the measurement of HU in preoperative CT.
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Affiliation(s)
- Jingchi Li
- grid.412901.f0000 0004 1770 1022Department of Orthopedic Surgery and Orthopedic Research Institute, West China Hospital/West China School of Medicine, Sichuan University, 37# Wuhou Guoxue Road, Chengdu, 610041 Sichuan Province People’s Republic of China
| | - Zhuang Zhang
- grid.412901.f0000 0004 1770 1022Department of Orthopedic Surgery and Orthopedic Research Institute, West China Hospital/West China School of Medicine, Sichuan University, 37# Wuhou Guoxue Road, Chengdu, 610041 Sichuan Province People’s Republic of China
| | - Tianhang Xie
- grid.412901.f0000 0004 1770 1022Department of Orthopedic Surgery and Orthopedic Research Institute, West China Hospital/West China School of Medicine, Sichuan University, 37# Wuhou Guoxue Road, Chengdu, 610041 Sichuan Province People’s Republic of China
| | - Zhetao Song
- grid.13291.380000 0001 0807 1581Department of Imaging, Sichuan University, Chengdu, Sichuan People’s Republic of China
| | - Yueming Song
- Department of Orthopedic Surgery and Orthopedic Research Institute, West China Hospital/West China School of Medicine, Sichuan University, 37# Wuhou Guoxue Road, Chengdu, 610041, Sichuan Province, People's Republic of China.
| | - Jiancheng Zeng
- Department of Orthopedic Surgery and Orthopedic Research Institute, West China Hospital/West China School of Medicine, Sichuan University, 37# Wuhou Guoxue Road, Chengdu, 610041, Sichuan Province, People's Republic of China.
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Xu C, Huang C, Cai P, Fang Z, Wei Z, Liu F, Li J, Liu Y. Biomechanical Effects of Pedicle Screw Positioning on the Surgical Segment in Models After Oblique Lumbar Interbody Fusion: An in-silico Study. Int J Gen Med 2022; 15:1047-1056. [PMID: 35140507 PMCID: PMC8818966 DOI: 10.2147/ijgm.s352304] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Accepted: 01/20/2022] [Indexed: 11/23/2022] Open
Abstract
Background Bilateral pedicle screw (BPS) is the “gold standard” of fixation methods for patients with lumbar interbody fusion. Biomechanical deterioration initially triggers complications in the surgical segment. Studies proved that BPS positions and trajectory changes affect the local biomechanical environment. However, no study illustrates the biomechanical effect of insertional screw positions’ change on the surgical segment. Methods Oblique lumbar interbody fusion (OLIF) with different BPS insertional positions has been simulated in a well-validated lumbo-sacral model. Fixation stability and stress responses on the surgical segment were evaluated under identical loading conditions. Results There is no clear variation tendency for the risk of BPS failure and the change of strain energy density of the grafted bone. However, shifting the insertional screw position close to the surgical segment will increase the range of motions (ROM) in the surgical segment and lead to stress concentration of bony structures, especially in the caudal side of the surgical segment. Conclusion Adjusting the insertional position of BPS close to the surgical segment in OLIF models will lead to stress concentration of bony structures and surgical segmental instability. Therefore, reducing BPS’s fixation length was not recommended, which may increase the risk of segmental instability, non-union, and cage subsidence.
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Affiliation(s)
- Chen Xu
- Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, Shanghai, 200003, People’s Republic of China
| | - Chenyi Huang
- Department of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, Luzhou, 646000, Sichuan, People’s Republic of China
| | - Ping Cai
- Department of Orthopedics, Affiliated Hospital of Nanjing University of Chinese Medicine, Nanjing, Jiangsu, People’s Republic of China
| | - Zhongxin Fang
- Fluid and Power Machinery Key Laboratory of Ministry of Education, Xihua University, Chengdu, People’s Republic of China
| | - Zhangchao Wei
- Department of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, Luzhou, 646000, Sichuan, People’s Republic of China
| | - Fei Liu
- Department of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, Luzhou, 646000, Sichuan, People’s Republic of China
| | - Jingchi Li
- Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, Shanghai, 200003, People’s Republic of China
- Department of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, Luzhou, 646000, Sichuan, People’s Republic of China
- Jingchi Li, Department of Orthopedics, Hospital (T.C.M) Affiliated to Southwest Medical University, No. 182, Chunhui Road, Luzhou, Sichuan Province, 646000, People’s Republic of China, Email
| | - Yang Liu
- Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, Shanghai, 200003, People’s Republic of China
- Correspondence: Yang Liu, Department of Spine Surgery, Shanghai Changzheng Hospital, Naval Medical University, 415th Fengyang Road, Shanghai, 200003, People’s Republic of China, Email
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Shekouhi N, Dick D, Baechle MW, Kaeley DK, Goel VK, Serhan H, Rawlinson J, Shaw D. Clinically relevant finite element technique based protocol to evaluate growing rods for early onset scoliosis correction. JOR Spine 2020; 3:e1119. [PMID: 33015580 PMCID: PMC7524209 DOI: 10.1002/jsp2.1119] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Revised: 05/20/2020] [Accepted: 07/22/2020] [Indexed: 02/06/2023] Open
Abstract
OBJECTIVE The emergence of distraction-based growing rods has provided the means to reduce the progression of spinal deformity in early onset scoliosis (EOS). The current protocols for evaluating spinal implants (ie, ASTM-F1717 and ISO-12189) were developed for fusion/dynamic devices. These protocols do not feature long unsupported rod lengths subjected to distraction. Due to the unsuitability of the existing guidelines for the evaluation of growing rods, a new distraction-based finite element protocol is presented herein for the first time. METHOD A vertebrectomy (VO) model from current protocols was modified to accommodate multi-spinal segments (ie, MS model) in which springs with appropriate stiffness were simulated in between the plastic blocks. To assess the efficacy of the protocol, two different computational studies were conducted: (a) compression-bending (MS-CB) with no distraction, and (b) distraction followed by compression-bending (MS-D + CB). In each study, the model with no axial connector (rods-only) was modified to include a) 80-mm long tandem (LT) connectors, and b) side-by-side (SBS) connectors. Stiffness and yield loads were calculated as per ASTM-F1717 guidelines and compared with the corresponding VO models with no distraction. In the MS-D + CB models, distraction was applied at the top block, stretching the spring-block construct in a simulation of scoliosis surgery prior to locking the construct at the connector-rods' interface. RESULTS MS-CB models predicted higher stiffness and yield loads, compared to the VO models. The locking mechanism produced pre-existing stresses on the rod-connector interface, which caused a shift in the location of high-stress regions to the distraction site. Distraction led to a decrease in the construct's stiffness and yield load. DISCUSSION The proposed protocol enables the simulation of clinical parameters that are not feasible in the F1717 models and predicted stress patterns in the hardware consistent with observed clinical failures.
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Affiliation(s)
- Niloufar Shekouhi
- Engineering Center for Orthopedic Research Excellence (E-CORE) University of Toledo Toledo, Ohio USA
| | - David Dick
- Engineering Center for Orthopedic Research Excellence (E-CORE) University of Toledo Toledo, Ohio USA
| | - Maxwell William Baechle
- Engineering Center for Orthopedic Research Excellence (E-CORE) University of Toledo Toledo, Ohio USA
| | - Dilpreet Kaur Kaeley
- Engineering Center for Orthopedic Research Excellence (E-CORE) University of Toledo Toledo, Ohio USA
| | - Vijay K Goel
- Engineering Center for Orthopedic Research Excellence (E-CORE) University of Toledo Toledo, Ohio USA
| | - Hassan Serhan
- Prestige Adjunct Professor, Departments of Bioengineering and Orthopaedic Surgery University of Toledo Toledo Ohio USA
| | | | - Derek Shaw
- Principal Engineer, Research and Testing NPD Team Lead DePuy Synthes Spine Raynham Massachusetts USA
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Chu YL, Chen CH, Tsuang FY, Chiang CJ, Wu Y, Kuo YJ. Incomplete insertion of pedicle screws in a standard construct reduces the fatigue life: A biomechanical analysis. PLoS One 2019; 14:e0224699. [PMID: 31675364 PMCID: PMC6824572 DOI: 10.1371/journal.pone.0224699] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Accepted: 10/19/2019] [Indexed: 12/05/2022] Open
Abstract
Pedicle screws are commonly used for posterior stabilization of the spine. When used in deformed or degenerated segments, the pedicle screws are often not fully inserted into the bone, but instead the threaded portion is exposed by 1 or 2 threads to accommodate rod placement and ensure alignment between the tulip of the screw and the rod. However, broken pedicle screws have been reported with the use of this method. The aim of this study was to determine how the fatigue life of the screw is affected by not fully inserting the screw into the bone. Spinal constructs were evaluated in accordance with ASTM F1717. The following three screw positions were subjected to compression bending fatigue loading; (i) pedicle screw fully inserted in the test block with no threads exposed (EXP-T0), (ii) pedicle screw inserted with one thread exposed outside the test block (EXP-T1), (iii) pedicle screw inserted with two threads exposed outside the test block (EXP-T2). Corresponding finite element models FEM-T0, FEM-T1 and FEM-T2 were also constructed and subjected to the same axial loading as the experimental groups to analyze the stress distribution in the pedicle screws and rods. The results showed that under a 190 N axial load, the EXP-T0 group survived the full 5 million cycles, the EXP-T1 group failed at 3.7 million cycles on average and the EXP-T2 groups failed at 1.0 million cycles on average, while the fatigue strength of both the EXP-T1 and EXP-T2 groups was 170 N. The constructs failed through fracture of the pedicle screw. In comparison to the FEM-T0 model, the maximum von Mises stress on the pedicle screw in the FEM-T1 and FEM-T2 models increased by 39% and 58%, respectively. In conclusion, this study demonstrated a drastic decrease in the fatigue life of pedicle screws when they are not full inserted into the plastic block.
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Affiliation(s)
- Yo-Lun Chu
- Department of Orthopedic Surgery, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
| | - Chia-Hsien Chen
- Department of Orthopedics, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
- Department of Orthopedic Surgery, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
- Graduate Institute of Biomedical Materials and Tissue Engineering, College of Biomedical Engineering, Taipei Medical University, Taipei, Taiwan
| | - Fon-Yih Tsuang
- Division of Neurosurgery, Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan
| | - Chang-Jung Chiang
- Department of Orthopedics, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
- Department of Orthopedic Surgery, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Yueh Wu
- Department of Orthopedic Surgery, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
| | - Yi-Jie Kuo
- Department of Orthopedic Surgery, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
- Department of Orthopedic Surgery, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
- * E-mail:
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La Barbera L, Cianfoni A, Ferrari A, Distefano D, Bonaldi G, Villa T. Stent-Screw Assisted Internal Fixation of Osteoporotic Vertebrae: A Comparative Finite Element Analysis on SAIF Technique. Front Bioeng Biotechnol 2019; 7:291. [PMID: 31709250 PMCID: PMC6824407 DOI: 10.3389/fbioe.2019.00291] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 10/09/2019] [Indexed: 12/19/2022] Open
Abstract
Vertebral compression fractures are one of the most relevant clinical consequences caused by osteoporosis: one of the most common treatment for such fractures is vertebral augmentation through minimally invasive approaches (vertebroplasty or balloon-kyphoplasty). Unfortunately, these techniques still present drawbacks, such as re-fractures of the treated vertebral body with subsidence of the non-augmented portions or re-fracture of the non-augmented middle column at the junction with the augmented anterior column. A novel minimally-invasive augmentation technique, called Stent-Screw Assisted Internal Fixation, has been recently proposed for the treatment of severe osteoporotic and neoplastic fractures: this technique uses two vertebral body stents and percutaneous cannulated and fenestrated pedicular screws, through which cement is injected inside the expanded stents to achieve optimal stents' and vertebral body's filling. The role of the pedicle screws is to anchor the stents-cement complex to the posterior column, acting as a bridge across the middle column and preserving its integrity from possible collapse. In order to evaluate the potential of the new technique in restoring the load bearing capacity of the anterior and middle spinal columns and in reducing bone strains, a Finite Element model of an osteoporotic lumbar spine has been developed. Both standard vertebroplasty and Stent-Screw Assisted Internal Fixation have been simulated: simulations have been run taking into account everyday activities (standing and flexion) and comparison between the two techniques, in terms of strain distribution on vertebral endplates and posterior and anterior wall, was performed. Results show that Stent-Screw Assisted Internal Fixation significantly decrease the strain distribution on the superior EP and the cortical wall compared to vertebroplasty, possibly reducing the re-fracture risk of the middle-column at the treated level.
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Affiliation(s)
- Luigi La Barbera
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta," Politecnico di Milano, Milan, Italy.,Department of Mechanical Engineering, Polytechnique Montréal, Montreal, QC, Canada.,Sainte-Justine University Hospital Centre, Montreal, QC, Canada
| | - Alessandro Cianfoni
- Department of Neuroradiology, Neurocenter of Southern Switzerland, Lugano, Switzerland.,Department of Interventional and Diagnostic Neuroradiology, Inselspital, University Hospital of Bern, Bern, Switzerland
| | - Andrea Ferrari
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta," Politecnico di Milano, Milan, Italy
| | - Daniela Distefano
- Department of Neuroradiology, Neurocenter of Southern Switzerland, Lugano, Switzerland
| | | | - Tomaso Villa
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "G. Natta," Politecnico di Milano, Milan, Italy
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Stent Screw−Assisted Internal Fixation (SAIF) of Severe Lytic Spinal Metastases: A Comparative Finite Element Analysis of the SAIF Technique. World Neurosurg 2019; 128:e370-e377. [DOI: 10.1016/j.wneu.2019.04.154] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 04/17/2019] [Accepted: 04/17/2019] [Indexed: 12/19/2022]
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Evaluation of iliac screw, S2 alar-iliac screw and laterally placed triangular titanium implants for sacropelvic fixation in combination with posterior lumbar instrumentation: a finite element study. 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 2019; 28:1724-1732. [PMID: 31093749 DOI: 10.1007/s00586-019-06006-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 04/10/2019] [Accepted: 05/09/2019] [Indexed: 02/07/2023]
Abstract
PURPOSE This study aimed to implement laterally placed triangular titanium implants as a technique of sacropelvic fixation in long posterior lumbar instrumentation and to characterize the effects of iliac screws, S2 alar-iliac screws and of triangular implants on rod and S1 pedicle screw stresses. METHODS Four female models of the lumbopelvic spine were created. For each of them, five finite element models replicating the following configurations were generated: intact, posterior fixation with pedicle screws to S1 (PED), with PED and iliac screws (IL), with PED and S2 alar-iliac (S2AI) screws, and with PED and bilateral triangular titanium implants (SI). Simulations were conducted in compression, flexion-extension, lateral bending and axial rotation. Rod stresses in the L5-S1 segment as well as in the S1 pedicle screws were compared. RESULTS One anatomical model was not simulated due to dysmorphia of the sacroiliac joints. PED resulted in the highest implant stresses. Values up to 337 MPa in lateral bending were noted, which were more than double than the other configurations. When compared with IL, S2AI and SI resulted in lower stresses in both screws and rods (on average 33% and 41% for S2AI and 17% and 50% for SI). CONCLUSIONS Implant stresses after S2AI and SI fixations were lower than those attributable to IL. Therefore, pedicle screws and rods may have a lower risk of mechanical failure when coupled with sacropelvic fixation via S2AI or triangular titanium implants, although the risk of clinical loosening remains an area of further investigation. These slides can be retrieved under Electronic Supplementary Material.
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La Barbera L, Villa T. Toward the definition of a new worst-case paradigm for the preclinical evaluation of posterior spine stabilization devices. Proc Inst Mech Eng H 2017; 231:176-185. [PMID: 28095745 DOI: 10.1177/0954411916684365] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Mechanical reliability tests on posterior spine stabilization devices are based on standard F1717 by the American Society for Testing and Materials, which describes how to assemble the implant with vertebrae-like test blocks in a corpectomy model. A recent study proposed to revise the standard to describe the anatomical worst-case scenario, instead of the average one currently implemented, and introduce the unsupported screw length as a mechanical parameter. This article investigates the implications of such revisions on the endurance properties of an implant already on the market. Experimental fatigue tests demonstrate that the revision of F1717 standard leads to a reduction of 3.2 million cycles in the fatigue strength of the tested implant: this amount is comparable to the run-out number of cycles (5 million cycles) currently recommended. The numerical analysis, validated with static tests and strain gauges, supports the experimental findings and demonstrates that the stress on the implant may increase upon revision up to a 50% on the screw (most recurrent failure mode), with the unsupported screw length contributing alone up to 40%. The revision of ASTM F1717 standard would guarantee higher safety for the implant to test, potentially covering for a wider population of patients.
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Affiliation(s)
- Luigi La Barbera
- 1 Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta," Politecnico di Milano, Milan, Italy.,2 IRCCS Galeazzi Orthopedic Institute, Milan, Italy
| | - Tomaso Villa
- 1 Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta," Politecnico di Milano, Milan, Italy.,2 IRCCS Galeazzi Orthopedic Institute, Milan, Italy
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11
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La Barbera L, Galbusera F, Wilke HJ, Villa T. Preclinical evaluation of posterior spine stabilization devices: can we compare in vitro and in vivo loads on the instrumentation? 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; 26:200-209. [DOI: 10.1007/s00586-016-4766-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Revised: 08/05/2016] [Accepted: 08/31/2016] [Indexed: 12/28/2022]
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12
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La Barbera L, Galbusera F, Wilke HJ, Villa T. Preclinical evaluation of posterior spine stabilization devices: can the current standards represent basic everyday life activities? 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; 25:2909-18. [PMID: 27236658 DOI: 10.1007/s00586-016-4622-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Revised: 05/19/2016] [Accepted: 05/19/2016] [Indexed: 12/19/2022]
Abstract
PURPOSE To discuss whether the available standard methods for preclinical evaluation of posterior spine stabilization devices can represent basic everyday life activities and how to compare the results obtained with different procedures. METHODS A comparative finite element study compared ASTM F1717 and ISO 12189 standards to validated instrumented L2-L4 segments undergoing standing, upper body flexion and extension. The internal loads on the spinal rod and the maximum stress on the implant are analysed. RESULTS ISO recommended anterior support stiffness and force allow for reproducing bending moments measured in vivo on an instrumented physiological segment during upper body flexion. Despite the significance of ASTM model from an engineering point of view, the overly conservative vertebrectomy model represents an unrealistic worst case scenario. A method is proposed to determine the load to apply on assemblies with different anterior support stiffnesses to guarantee a comparable bending moment and reproduce specific everyday life activities. CONCLUSIONS The study increases our awareness on the use of the current standards to achieve meaningful results easy to compare and interpret.
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Affiliation(s)
- Luigi La Barbera
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milan, Italy.
- IRCCS Galeazzi Orthopaedic Institute, via Riccardo Galeazzi 4, 20161, Milan, Italy.
| | - Fabio Galbusera
- IRCCS Galeazzi Orthopaedic Institute, via Riccardo Galeazzi 4, 20161, Milan, Italy
| | - Hans-Joachim Wilke
- Institute of Orthopaedic Research and Biomechanics, Centre of Musculoskeletal Research Ulm, Ulm University, Helmholtzstrasse 14, 89081, Ulm, Germany
| | - Tomaso Villa
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milan, Italy
- IRCCS Galeazzi Orthopaedic Institute, via Riccardo Galeazzi 4, 20161, Milan, Italy
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La Barbera L, Villa T. ISO 12189 standard for the preclinical evaluation of posterior spinal stabilization devices--I: Assembly procedure and validation. Proc Inst Mech Eng H 2015; 230:122-33. [PMID: 26679431 DOI: 10.1177/0954411915621587] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Accepted: 11/16/2015] [Indexed: 12/29/2022]
Abstract
The International Standardization Organization introduced standard 12189 for the preclinical evaluation of the mechanical reliability of posterior stabilization devices. The well-known vertebrectomy model formalized in standard F1717 by the American Society for Testing and Materials was modified with the introduction of a modular anterior support made up of three calibrated springs, which allows to describe a more realistic scenario, closer to the effective clinical use, as well to test even very flexible and dynamic posterior stabilization implants. Despite these important improvements, ISO 12189 received very little attention in the literature. The aim of the work is to provide a systematic procedure for the assembly and validation of a finite element model capable of describing the experimental test according to ISO 12189. The validated finite element model is able to catch very well the effective stiffness of the unassembled and assembled constructs (percentage differences <2% and <10%, respectively). As concern the assembled construct, the experimentally measured and predicted strains were found in a good agreement (R2 > 0.75, root mean square error < 30%), but the procedure without precompression lead to much better results (R2 > 0.96, root mean square error < 10%). Given the prediction errors of the assembled construct fall within the experimental range of repeatability, the finite element model can be systematically implemented to support the mechanical design of a variety of spinal implants, to quantitatively investigate the load-sharing mechanism, as well as to investigate the loading conditions set by ISO 12189 standard.
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Affiliation(s)
- Luigi La Barbera
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering 'Giulio Natta', Politecnico di Milano, Milano, Italy IRCCS Istituto Ortopedico Galeazzi, Milano, Italy
| | - Tomaso Villa
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering 'Giulio Natta', Politecnico di Milano, Milano, Italy IRCCS Istituto Ortopedico Galeazzi, Milano, Italy
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