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Tsagkaris C, Calek AK, Fasser MR, Spirig JM, Caprara S, Farshad M, Widmer J. Bone density optimized pedicle screw insertion. Front Bioeng Biotechnol 2023; 11:1270522. [PMID: 37954015 PMCID: PMC10639121 DOI: 10.3389/fbioe.2023.1270522] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 09/19/2023] [Indexed: 11/14/2023] Open
Abstract
Background: Spinal fusion is the most common surgical treatment for the management of degenerative spinal disease. However, complications such as screw loosening lead to painful pseudoarthrosis, and are a common reason for revision. Optimization of screw trajectories to increase implant resistance to mechanical loading is essential. A recent optimization method has shown potential for determining optimal screw position and size based on areas of high bone elastic modulus (E-modulus). Aim: The aim of this biomechanical study was to verify the optimization algorithm for pedicle screw placement in a cadaveric study and to quantify the effect of optimization. The pull-out strength of pedicle screws with an optimized trajectory was compared to that of a traditional trajectory. Methods: Twenty-five lumbar vertebrae were instrumented with pedicle screws (on one side, the pedicle screws were inserted in the traditional way, on the other side, the screws were inserted using an optimized trajectory). Results: An improvement in pull-out strength and pull-out strain energy of the optimized screw trajectory compared to the traditional screw trajectory was only observed for E-modulus values greater than 3500 MPa cm3. For values of 3500 MPa cm3 or less, optimization showed no clear benefit. The median screw length of the optimized pedicle screws was significantly smaller than the median screw length of the traditionally inserted pedicle screws, p < 0.001. Discussion: Optimization of the pedicle screw trajectory is feasible, but seems to apply only to vertebrae with very high E-modulus values. This is likely because screw trajectory optimization resulted in a reduction in screw length and therefore a reduction in the implant-bone interface. Future efforts to predict the optimal pedicle screw trajectory should include screw length as a critical component of potential stability.
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Affiliation(s)
- Christos Tsagkaris
- Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
| | - Anna-Katharina Calek
- Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
- Spine Biomechanics, Department of Orthopedic Surgery, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
| | - Marie-Rosa Fasser
- Spine Biomechanics, Department of Orthopedic Surgery, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - José Miguel Spirig
- University Spine Center Zurich, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
| | - Sebastiano Caprara
- Spine Biomechanics, Department of Orthopedic Surgery, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - Mazda Farshad
- Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
- University Spine Center Zurich, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
| | - Jonas Widmer
- Spine Biomechanics, Department of Orthopedic Surgery, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
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Zheng J, Liu F, Xiang J, Leung FKL, Feng X, Chen B. Biomechanical investigation of S2 alar-iliac screw and S1 pedicle screw fixation in the treatment of Denis type II sacral fractures. J Orthop Res 2023; 41:215-224. [PMID: 35441729 DOI: 10.1002/jor.25336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 02/24/2022] [Accepted: 03/31/2022] [Indexed: 02/04/2023]
Abstract
Although S2 alar-iliac screw technique has been widely used in spinal surgery, its applicability to pelvic fractures is largely unknown. This study aimed to evaluate the biomechanical stability of S2 alar-iliac screw and S1 pedicle screw fixation in the treatment of Denis II sacral fractures. Twenty-eight artificial pelvic fracture models were treated with unilateral lumbopelvic fixation, sacroiliac screw fixation, S2 alar-iliac screw and S1 pedicle screw fixation, and S2 alar-iliac screw and contralateral S1 pedicle screw fixation (Groups 1-4, respectively; N = 7 per group). Each model was cyclically tested under increasing axial compression. Optical motion-tracking was used to assess relative displacement and gap angle, and the number of failure cycles. Relative displacement was significantly smaller in Group 3 than in Groups 1 (p = 0.004) and 4 (p < 0.001) but not significantly different between Groups 3 and 2 (p = 0.290). The gap angle in Group 3 was significantly smaller than that in Group 1 (p = 0.009) on the sagittal plane but significantly larger than that in Group 4 (p = 0.006) on the horizontal plane. A number of failure cycles was significantly higher in Group 3 than in Groups 1 (p = 0.002) and 4 (p = 0.004) but not significantly different between Groups 3 and 2 (p = 0.910). From a biomechanical perspective, S2 alar-iliac screw and S1 pedicle screw fixation can provide good stability in the treatment of Denis II sacral fractures.
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Affiliation(s)
- Jianxiong Zheng
- Division of Orthopaedics and Traumatology, Department of Orthopaedics, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Fei Liu
- Division of Orthopaedics and Traumatology, Department of Orthopaedics, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Jie Xiang
- Division of Orthopaedics and Traumatology, Department of Orthopaedics, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Frankie K L Leung
- Department of Orthopaedics and Traumatology, Queen Mary Hospital, The University of Hong Kong, Pok Fu Lam, Hong Kong
| | - Xiaoreng Feng
- Division of Orthopaedics and Traumatology, Department of Orthopaedics, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Bin Chen
- Division of Orthopaedics and Traumatology, Department of Orthopaedics, Nanfang Hospital, Southern Medical University, Guangzhou, China
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3
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Aycan MF, Arslan AK, Uslan Y, Demir T. Postfusion effect on pullout strength of pedicle screws with expandablepeek shell and conventional screws. Acta Orthop Belg 2022; 88:433-440. [PMID: 36791695 DOI: 10.52628/88.3.6855] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
The pullout performance of various pedicle screws after artificial fusion process was investigated in this study. Normal, cannulated (cemented), novel expandable and normal (cemented) pedicle screws were tested. Polyurethane foams (Grade 10 and Grade 40) produced by casting method were used as test materials. The instrumentation of pedicle screws has been carried out with production of foams, simultaneously. For cemented pedicle screws, 3D models were prepared with respect to the anteriosuperior and oblique radiographs by using PMMA before casting procedure. Pullout tests were performed in an Instron 3369 testing device. Load versus displacement graph was recorded and the ultimate force was defined as the pullout strength sustained before failure of screw. As expected, the pullout strengths of pedicle screws in postfusion are higher than before fusion. Pullout strengths increased significantly by artificial fusion in Grade 10 foams compared to Grade 40 foams. Additionally, while the pullout strengths of normal, cannulated and novel expandable pedicle screws increased by artificial fusion, cemented normal pedicle screws had lower pullout values than before fusion in Grade 40 foams. When the cemented normal pedicle screws are excluded, other screws have almost similar pullout strength level. On the other hand, the pedicle screws have different increasing behaviour also, there is no correlation between each other. As a result, the novel expandable pedicle screws can be used instead of normal and cannulated ones due to their performances in non-cemented usage.
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Wang Y, Yang L, Li C, Sun H. The Biomechanical Properties of Cement-Augmented Pedicle Screws for Osteoporotic Spines. Global Spine J 2022; 12:323-332. [PMID: 33611971 PMCID: PMC8907649 DOI: 10.1177/2192568220987214] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
STUDY DESIGN This is a broad, narrative review of the literature. OBJECTIVE In this review, we describe recent biomechanics studies on cement-augmented pedicle screws for osteoporotic spines to determine which factors influence the effect of cement augmentation. METHODS A search of Medline was performed, combining the search terms "pedicle screw" and ("augmentation" OR "cement"). Articles published in the past 5 years dealing with biomechanical testing were included. RESULTS Several factors have been identified to impact the effect of cement augmentation in osteoporotic spines. These include the type of augmentation material, the volume of injected cement, the timing of augmentation, the severity of osteoporosis, the design of the pedicle screw, and the specific augmenting technique, among others. CONCLUSIONS This review elaborates the biomechanics of cement-augmented pedicle screws, determines which factors influence the augmentation effect, and identifies the risk factors of cement leakage in osteoporotic bone, which might offer some guidance when using this technique in clinical practice. Further, we provide information about newly designed screws and recently developed augmentation materials that provide higher screw stability as well as fewer cement-related complications.
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Affiliation(s)
- Yuetian Wang
- Department of Orthopedics, Peking University First
Hospital, Beijing, China
| | - Lei Yang
- Center for Health Science and
Engineering(CHSE), School of Materials Science and Engineering, Hebei University of
Technology, Tianjin, China
| | - Chunde Li
- Department of Orthopedics, Peking University First
Hospital, Beijing, China
| | - Haolin Sun
- Department of Orthopedics, Peking University First
Hospital, Beijing, China,Haolin Sun, Peking University First
Hospital, Beijing 100034, China.
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Effect of cortical bone thickness and density on pullout strength of mini-implants: An experimental study. Am J Orthod Dentofacial Orthop 2020; 157:178-185. [DOI: 10.1016/j.ajodo.2019.02.020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Revised: 02/01/2019] [Accepted: 02/01/2019] [Indexed: 11/22/2022]
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Widmer J, Fasser MR, Croci E, Spirig J, Snedeker JG, Farshad M. Individualized prediction of pedicle screw fixation strength with a finite element model. Comput Methods Biomech Biomed Engin 2020; 23:155-167. [PMID: 31910656 DOI: 10.1080/10255842.2019.1709173] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Pedicle screws are used for the treatment of a wide variety of spinal pathologies. A good screw holding power in bone is required for treatment success, but has so far not been predictable computationally. The goal of this study was to develop an automated tool able to predict patient-specific screw fixation strength through finite element simulation. We compared the simulation results with results from biomechanical pull-out tests performed on animal lumbar specimens. Experimental and simulation pull-out strengths were highly correlated [Formula: see text] and the mean error was 20.25%. The fixation strength was also associated to great extent with pull-out stiffness and strain energy, as well as the screw size and mean vertebral density.
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Affiliation(s)
- Jonas Widmer
- Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland.,Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - Marie-Rosa Fasser
- Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland.,Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - Eleonora Croci
- Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland.,Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - José Spirig
- Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland
| | - Jess G Snedeker
- Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland.,Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - Mazda Farshad
- Department of Orthopaedics, Balgrist University Hospital, Zurich, Switzerland
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Khatri R, Varghese V, Sharma S, Kumar GS, Chhabra HS. Pullout Strength Predictor: A Machine Learning Approach. Asian Spine J 2019; 13:842-848. [PMID: 31154706 PMCID: PMC6773988 DOI: 10.31616/asj.2018.0243] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 03/10/2019] [Indexed: 11/29/2022] Open
Abstract
Study Design A biomechanical study. Purpose To develop a predictive model for pullout strength. Overview of Literature Spine fusion surgeries are performed to correct joint deformities by restricting motion between two or more unstable vertebrae. The pedicle screw provides a corrective force to the unstable spinal segment and arrests motions at the unit that are being fused. To determine the hold of a screw, surgeons depend on a subjective perioperative feeling of insertion torque. The objective of the paper was to develop a machine learning based model using density of foam, insertion angle, insertion depth, and reinsertion to predict the pullout strength of pedicle screw. Methods To predict the pullout strength of pedicle screw, an experimental dataset of 48 data points was used as training data to construct a model based on different machine learning algorithms. A total of five algorithms were tested in the Weka environment and the performance was evaluated based on correlation coefficient and error matrix. A sensitive study of various parameters for obtaining the best combination of parameters for predicting the pullout strength was also preformed using the L9 orthogonal array of Taguchi Design of Experiments. Results Random forest performed the best with a correlation coefficient of 0.96, relative absolute error of 0.28, and root relative squared error of 0.29. The difference between the experimental and predicted value for the six test cases was not significant (p >0.05). Conclusions This model can be used clinically for understanding the failure of pedicle screw pullout and pre-surgical planning for spine surgeon.
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Affiliation(s)
- Ravi Khatri
- Biomechanics Lab, Indian Spinal Injuries Centre, New Delhi, India.,Department of Engineering Design, IIT Madras, Chennai, India
| | - Vicky Varghese
- Biomechanics Lab, Indian Spinal Injuries Centre, New Delhi, India
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Testing Pullout Strength of Pedicle Screw Using Synthetic Bone Models: Is a Bilayer Foam Model a Better Representation of Vertebra? Asian Spine J 2018; 12:398-406. [PMID: 29879765 PMCID: PMC6002167 DOI: 10.4184/asj.2018.12.3.398] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 11/04/2017] [Accepted: 11/15/2017] [Indexed: 12/04/2022] Open
Abstract
Study Design A biomechanical study. Purpose A new biomechanical model of the vertebra has been developed that accounts for the inhomogeneity of bone and the contribution of the pedicle toward the holding strength of a pedicle screw. Overview of Literature Pullout strength studies are typically carried out on rigid polyurethane foams that represent the homogeneous vertebral framework of the spine. However, the contribution of the pedicle region, which contributes to the inhomogeneity in this framework, has not been considered in previous investigations. Therefore, we propose a new biomechanical model that can account for the vertebral inhomogeneity, especially the contribution of the pedicles toward the pullout strength of the pedicle screw. Methods A bilayer foam model was developed by joining two foams representing the pedicle and the vertebra. The results of the pullout strength tests performed on the foam models were compared with those from the tests performed on the cadaver lumbar vertebra. Results Significant differences (p <0.05) were observed between the pullout strength of the pedicle screw in extremely osteoporotic (0.18±0.11 kN), osteoporotic (0.37±0.14 kN), and normal (0.97±0.4 kN) cadaver vertebra. In the monolayer model, significant differences (p <0.05) were observed in pullout strength between extremely osteoporotic (0.3±0.02 kN), osteoporotic (0.65±0.12 kN), and normal (0.99±0.04 kN) bone model. However, the bilayer foam model exhibited no significant differences (p >0.05) in the pullout strength of pedicle screws between osteoporotic (0.85±0.08 kN) and extremely osteoporotic bone models (0.94±0.08 kN), but there was a significant difference (p <0.05) between osteoporotic (0.94±0.08 kN) and normal bone models (1.19±0.05 kN). There were no significant differences (p >0.05) in pullout strength between cadaver and bilayer foam model in normal bones. Conclusions The new synthetic bone model that reflects the contribution of the pedicles to the pullout strength of the pedicle screws could provide a more efficacious means of testing pedicle-screw pullout strength. The bilayer model can match the pullout strength value of normal lumbar vertebra bone whereas the monolayer foam model was able to match that of the extremely osteoporotic lumbar vertebra.
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Weng F, Wang J, Yang L, Zeng J, Chu Y, Tian Z. Application value of expansive pedicle screw in the lumbar short-segment fixation and fusion for osteoporosis patients. Exp Ther Med 2018; 16:665-670. [PMID: 30112031 PMCID: PMC6090430 DOI: 10.3892/etm.2018.6248] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Accepted: 05/22/2018] [Indexed: 12/25/2022] Open
Abstract
Clinical value of expansive pedicle screw in lumbar short-segment fixation and fusion for patients with osteoporosis was investigated. A total of 80 patients with lumbar compression fracture but without obvious nerve compression were selected and divided into the observation group (n=40) and the control group (n=40) using a random number table. The observation group used the expansive pedicle screw, and the control group received conventional pedicle screw fixation and bone graft fusion. In the observation group, the operation and hospitalization time after operation were shorter and the intraoperative bleeding amount was less than that in control group (p<0.05). At 1 week, 1, 3 and 6 months after operation, the observation group had better straight leg raising test (SLRT) scores, higher lower limb sensory scores but lower visual analogue scale (VAS) scores than control group (p<0.05). Besides, the proportions of postoperative infection, dural mater tear, nerve root injury and spinal cord injury during operation in the observation group were lower than those in the control group (p<0.05), and the bone graft fusion rates at 3 and 6 months after operation were obviously superior to those in control group (p<0.05). Moreover, after operation, the spinal stenosis rate in the observation group was lower than that in control group (p<0.05), the vertebral height ratio was larger than that in control group (p<0.05), and the Cobb's angle was smaller than that in the control group (p<0.05). In addition, there was a negative correlation between bone mineral density (BMD) and hospitalization time after operation in the observation group (p<0.05). In conclusion, the internal fixation with expansive pedicle screw for osteoporosis patients with lumbar compression fracture is characterized by short operation time, less intraoperative bleeding, few complications, quick recovery of postoperative neurological function and satisfactory surgical effect. However, reasonable intervention in osteoporosis is also necessary.
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Affiliation(s)
- Fengbiao Weng
- Department of Orthopaedics, The First People's Hospital of Wujiang District, Suzhou, Jiangsu 215200, P.R. China
| | - Jiazi Wang
- Department of Orthopaedics, The First People's Hospital of Wujiang District, Suzhou, Jiangsu 215200, P.R. China
| | - Liwen Yang
- Department of Orthopaedics, The First People's Hospital of Wujiang District, Suzhou, Jiangsu 215200, P.R. China
| | - Jincai Zeng
- Department of Orthopaedics, The First People's Hospital of Wujiang District, Suzhou, Jiangsu 215200, P.R. China
| | - Yawei Chu
- Department of Orthopaedics, The First People's Hospital of Wujiang District, Suzhou, Jiangsu 215200, P.R. China
| | - Zhigang Tian
- Department of Orthopaedics, The First People's Hospital of Wujiang District, Suzhou, Jiangsu 215200, P.R. China
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Aycan MF, Yaman ME, Usta Y, Demir T, Tolunay T. Investigation of toggling effect on pullout performance of pedicle screws. Proc Inst Mech Eng H 2018; 232:395-402. [DOI: 10.1177/0954411918755417] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Objective of this study is to assess the pullout performance of various pedicle screws in different test materials after toggling tests comparatively. Solid core, cannulated (cemented), novel expandable and solid-core (cemented) pedicle screws were instrumented to the polyurethane foams (Grade 10 and Grade 40) produced in laboratory and bovine vertebra. ASTM F543 standard was used for preparation process of samples. Toggling tests were carried out. After toggling test procedures, pullout tests were performed. Load versus displacement graph was recorded, and the ultimate pullout force was defined as the maximum load (pullout strength) sustained before failure of screw. Anteriosuperior and oblique radiographs were taken from each sample after instrumentation in order to examine screw placement and cement distribution. The pullout strength of pedicle screws decreased after toggling tests with respect to the initial condition. While the cemented solid-core pedicle screws had the highest pullout strength in all test materials, they had the highest strength differences. The cemented solid-core pedicle screws had decrement rates of 27% and 16% in Grade 10 and Grade 40, respectively. There are almost same decrement rate (between 5.5% and 6.5%) for all types of pedicle screws instrumented to the samples of bovine vertebra. The pullout strengths of novel expandable pedicle screws in both of early period and after toggling conditions were almost similar, in other words, the decrement rates of it were lower than other types. According to the data collected from this study, polymethylmethacrylate augmentation significantly decreases pullout strength following the toggling loads. Higher brittleness of cured polymethylmethacrylate has adverse effect on the pullout strength. Although augmentation is an important process for enhancing pullout strength in early period, it has some disadvantages for preserving stabilization in a long time. Expandable pedicle screw with polyetheretherketone shell may be good alternative to polymethylmethacrylate augmentation on both primer stabilization and long-term loading application with toggling.
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Affiliation(s)
| | - Mesut Emre Yaman
- Department of Neurosurgery, Memorial Ankara Hospital, Ankara, Turkey
| | - Yusuf Usta
- Department of Mechanical Engineering, Gazi University, Ankara, Turkey
| | - Teyfik Demir
- Department of Mechanical Engineering, TOBB University of Economics and Technology, Ankara, Turkey
| | - Tolga Tolunay
- Department of Orthopedics, Yıldırım Beyazıt University, Ankara, Turkey
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Van den Abbeele M, Valiadis JM, Lima LVPC, Khalifé P, Rouch P, Skalli W. Contribution to FE modeling for intraoperative pedicle screw strength prediction. Comput Methods Biomech Biomed Engin 2017; 21:13-21. [PMID: 29226718 DOI: 10.1080/10255842.2017.1414200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Although the use of pedicle screws is considered safe, mechanical issues still often occur. Commonly reported issues are screw loosening, screw bending and screw fracture. The aim of this study was to develop a Finite Element (FE) model for the study of pedicle screw biomechanics and for the prediction of the intraoperative pullout strength. The model includes both a parameterized screw model and a patient-specific vertebra model. Pullout experiments were performed on 30 human cadaveric vertebrae from ten donors. The experimental force-displacement data served to evaluate the FE model performance. μCT images were taken before and after screw insertion, allowing the creation of an accurate 3D-model and a precise representation of the mechanical properties of the bone. The experimental results revealed a significant positive correlation between bone mineral density (BMD) and pullout strength (Spearman ρ = 0.59, p < 0.001) as well as between BMD and pullout stiffness (Spearman ρ = 0.59, p < 0.001). A high positive correlation was also found between the pullout strength and stiffness (Spearman ρ = 0.84, p < 0.0001). The FE model was able to reproduce the linear part of the experimental force-displacement curve. Moreover, a high positive correlation was found between numerical and experimental pullout stiffness (Pearson ρ = 0.96, p < 0.005) and strength (Pearson ρ = 0.90, p < 0.05). Once fully validated, this model opens the way for a detailed study of pedicle screw biomechanics and for future adjustments of the screw design.
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Affiliation(s)
- Maxim Van den Abbeele
- a Institut de Biomécanique Humaine Georges Charpak , Arts et Métiers ParisTech , 151, Boulevard de l'Hopital, Paris , 75013 , France
| | - Jean-Marc Valiadis
- a Institut de Biomécanique Humaine Georges Charpak , Arts et Métiers ParisTech , 151, Boulevard de l'Hopital, Paris , 75013 , France
| | - Lucas V P C Lima
- a Institut de Biomécanique Humaine Georges Charpak , Arts et Métiers ParisTech , 151, Boulevard de l'Hopital, Paris , 75013 , France
| | - Pascal Khalifé
- a Institut de Biomécanique Humaine Georges Charpak , Arts et Métiers ParisTech , 151, Boulevard de l'Hopital, Paris , 75013 , France
| | - Philippe Rouch
- a Institut de Biomécanique Humaine Georges Charpak , Arts et Métiers ParisTech , 151, Boulevard de l'Hopital, Paris , 75013 , France
| | - Wafa Skalli
- a Institut de Biomécanique Humaine Georges Charpak , Arts et Métiers ParisTech , 151, Boulevard de l'Hopital, Paris , 75013 , France
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12
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Insufficient stability of pedicle screws in osteoporotic vertebrae: biomechanical correlation of bone mineral density and pedicle screw fixation strength. 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 2017; 26:2891-2897. [PMID: 28391382 DOI: 10.1007/s00586-017-5091-x] [Citation(s) in RCA: 101] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 03/20/2017] [Accepted: 04/05/2017] [Indexed: 01/23/2023]
Abstract
PURPOSE Loosening of pedicle screws is one major complication of posterior spinal stabilisation, especially in the patients with osteoporosis. Augmentation of pedicle screws with cement or lengthening of the instrumentation is widely used to improve implant stability in these patients. However, it is still unclear from which value of bone mineral density (BMD) the stability of pedicle screws is insufficient and an additional stabilisation should be performed. The aim of this study was to investigate the correlation of bone mineral density and pedicle screw fatigue strength as well as to define a threshold value for BMD below which an additional stabilisation is recommended. METHODS Twenty-one human T12 vertebral bodies were collected from donors between 19 and 96 years of age and the BMD was measured using quantitative computed tomography. Each vertebral body was instrumented with one pedicle screw and mounted in a servo-hydraulic testing machine. Fatigue testing was performed by implementing a cranio-caudal sinusoidal, cyclic (0.5 Hz) load with stepwise increasing peak force. RESULTS A significant correlation between BMD and cycles to failure (r = 0.862, r 2 = 0.743, p < 0.001) as well as for the linearly related fatigue load was found. Specimens with BMD below 80 mg/cm3 only reached 45% of the cycles to failure and only 60% of the fatigue load compared to the specimens with adequate bone quality (BMD > 120 mg/cm3). CONCLUSIONS There is a close correlation between BMD and pedicle screw stability. If the BMD of the thoracolumbar spine is less than 80 mg/cm3, stability of pedicle screws might be insufficient and an additional stabilisation should be considered.
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Schmoelz W, Heinrichs CH, Schmidt S, Piñera AR, Tome-Bermejo F, Duart JM, Bauer M, Galovich LÁ. Timing of PMMA cement application for pedicle screw augmentation affects screw anchorage. 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 2017; 26:2883-2890. [PMID: 28374330 DOI: 10.1007/s00586-017-5053-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 03/13/2017] [Accepted: 03/17/2017] [Indexed: 12/26/2022]
Abstract
INTRODUCTION Cement augmentation is an established method to increase the pedicle screw (PS) anchorage in osteoporotic vertebral bodies. The ideal timing for augmentation when a reposition maneuver is necessary is controversial. While augmentation of the PS before reposition maneuver may increase the force applied it on the vertebrae, it bears the risk to impair PS anchorage, whereas augmenting the PS after the maneuver may restore this anchorage and prevent early screw loosening. The purpose of the present study was to evaluate the effect of cement application timing on PS anchorage in the osteoporotic vertebral body. METHODS Ten lumbar vertebrae (L1-L5) were used for testing. The left and right pedicles of each vertebra were instrumented with the same PS size and used for pairwise comparison of the two timing points for augmentation. For the reposition maneuver, the left PS was loaded axially under displacement control (2 × ±2 mm, 3 × ±6 mm, 3 × ±10 mm) to simulate a reposition maneuver. Subsequently, both PS were augmented with 2 ml PMMA cement. The same force as measured during the left PS maneuver was applied to the previously augmented right hand side PS [2 × F (±2 mm), 3 × F (±6 mm), 3 × F (±10 mm)]. Both PS were cyclically loaded with initial forces of +50 and -50 N, while the lower force was increased by 5 N every 100 cycles until total failure of the PS. The PS motion was measured with a 3D motion analysis system. After cyclic loading stress, X-rays were taken to identify the PS loosening mechanism. RESULTS In comparison with PS augmented prior to the reposition maneuver, PS augmented after the reposition maneuver showed a significant higher number of load cycles until failure (5930 ± 1899 vs 3830 ± 1706, p = 0.015). The predominant loosening mechanism for PS augmented after the reposition maneuver was PS toggling with the attached cement cloud within the trabecular bone. While PS augmented prior to the reposition, maneuver showed a motion of the screw within the cement cloud. CONCLUSION The time of cement application has an effect on PS anchorage in the osteoporotic vertebral body if a reposition maneuver of the instrumented vertebrae is carried out. PS augmented after the reposition maneuver showed a significant higher number of load cycles until screw loosening.
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Affiliation(s)
- Werner Schmoelz
- Department of Trauma Surgery, Medical University of Innsbruck, Anichstrasse 35, 6020, Innsbruck, Austria.
| | - Christian Heinz Heinrichs
- Department of Trauma Surgery, Medical University of Innsbruck, Anichstrasse 35, 6020, Innsbruck, Austria
| | - Sven Schmidt
- Orthopaedic University Hospital Friedrichsheim, Frankfurt am Main, Germany
| | - Angel R Piñera
- Spine Service, Fundacion Jimenez Diaz University Hospital, Madrid, Spain
| | - Felix Tome-Bermejo
- Spine Service, Fundacion Jimenez Diaz University Hospital, Madrid, Spain
| | - Javier M Duart
- Spine Service, Fundacion Jimenez Diaz University Hospital, Madrid, Spain
| | - Marlies Bauer
- Division of Clinical and Functional Anatomy, Department of Anatomy, Histology and Embryology, Medical University of Innsbruck, Innsbruck, Austria
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