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Thelen S, Oezel L, Hilss L, Grassmann JP, Betsch M, Wild M. Is restoration of vertebral body height after vertebral body fractures and minimally-invasive dorsal stabilization with polyaxial pedicle screws just an illusion? Arch Orthop Trauma Surg 2024; 144:239-250. [PMID: 37838983 PMCID: PMC10774198 DOI: 10.1007/s00402-023-05082-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 09/18/2023] [Indexed: 10/17/2023]
Abstract
INTRODUCTION Thoracolumbar spine fractures often require surgical treatment as they are associated with spinal instability. Optimal operative techniques and treatment are discussed controversially. Aim of our prospective cohort study was to investigate the sagittal alignment after reduction, the secondary loss of reduction and the subjective outcome as well as the causal correlation of these parameters after minimally invasive stabilization of thoracic and lumbar fractures with polyaxial pedicle screws. MATERIALS AND METHODS In a single-center study, a total of 78 patients with an average age of 61 ± 17 years who suffered a fracture of the thoracic or lumbar spine were included and subjected to a clinical and radiological follow-up examination after 8.5 ± 8 months. The kyphotic deformity was measured by determining the vertebral body angle, the mono- and bi-segmental wedge angle at three time points. The patients' subjective outcome was evaluated by the VAS spine score. RESULTS After surgical therapy, a significant reduction of the traumatic kyphotic deformity was shown with an improvement of all angles (vertebral body angle: 3.2° ± 4.4°, mono- and bi-segmental wedge angle: 3.1° ± 5.6°, 2.0° ± 6.3°). After follow-up, a significant loss of sagittal alignment was observed for all measured parameters with a loss of correction. However, no correlation between the loss of reduction and the subjective outcome regarding the VAS spine scale could be detected. CONCLUSION The minimally invasive dorsal stabilization of thoracic and lumbar spine fractures with polyaxial pedicle screws achieved a satisfactory reduction of the fracture-induced kyphotic deformity immediately postoperatively with a floss of reduction in the further course. However, maybe the main goal of this surgical procedure should be the prevention of a complete collapse of the vertebral body instead of a long-lasting restoration of anatomic sagittal alignment. LEVEL OF EVIDENCE II.
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Affiliation(s)
- Simon Thelen
- Department of Orthopaedics and Trauma Surgery, University Hospital Duesseldorf, Moorenstraße 5, 40225, Duesseldorf, Germany
| | - Lisa Oezel
- Department of Orthopaedics and Trauma Surgery, University Hospital Duesseldorf, Moorenstraße 5, 40225, Duesseldorf, Germany.
| | - Lena Hilss
- Department of Orthopaedics, Trauma- and Hand Surgery, Klinikum Darmstadt, Darmstadt, Germany
| | - Jan-Peter Grassmann
- Department of Orthopaedics and Trauma Surgery, University Hospital Duesseldorf, Moorenstraße 5, 40225, Duesseldorf, Germany
| | - Marcel Betsch
- Department of Orthopaedics and Trauma Surgery, University Hospital Erlangen, Erlangen, Germany
| | - Michael Wild
- Department of Orthopaedics, Trauma- and Hand Surgery, Klinikum Darmstadt, Darmstadt, Germany
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Ferreira DRC, Dias LGGG, Minto BW, Rocha TASDS, Malta CADS, da Conceição MEBAM, de Lucena DVF. Biomechanical evaluation of four surgical techniques for ventral stabilization of the atlantoaxial joint in dogs. Acta Cir Bras 2023; 38:e383223. [PMID: 37729349 PMCID: PMC10508196 DOI: 10.1590/acb383223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Accepted: 06/18/2023] [Indexed: 09/22/2023] Open
Abstract
PURPOSE This study compared, through biomechanical evaluation under ventral flexion load, four surgical techniques for ventral stabilization of the atlantoaxial joint in dogs. METHODS In total, 28 identical atlantoaxial joint models were created by digital printing from computed tomography images of a dog, and the specimens were divided into four groups of seven. In each group, a different technique for ventral stabilization of the atlantoaxial joint was performed: transarticular lag screws, polyaxial screws, multiple screws and bone cement (polymethylmethacrylate-PMMA), and atlantoaxial plate. After the stabilization technique, biomechanical evaluation was performed under ventral flexion load, both with a predefined constant load and with a gradually increasing load until stabilization failure. RESULTS All specimens, regardless of stabilization technique, were able to support the predefined load without failing. However, the PMMA method provided significant more rigidity (p ≤ 0.05) and also best resisted the gradual increase in load, supporting a significantly higher maximum force (p ≤ 0.05). There was no statistical difference in flexural strength between the transarticular lag screws and plate groups. The polyaxial screws method was significantly less resistant to loading (p ≤ 0.05) than the other groups. CONCLUSIONS The PMMA technique had biomechanical advantages in ventral atlantoaxial stabilization over the other evaluated methods.
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Affiliation(s)
- Danyelle Rayssa Cintra Ferreira
- Universidade Estadual Paulista “Júlio de Mesquita Filho” – Faculdade de Ciências Agrárias e Veterinárias – Department of Veterinary Medicine and Surgery – Jaboticabal (São Paulo) – Brazil
| | - Luís Gustavo Gosuen Gonçalves Dias
- Universidade Estadual Paulista “Júlio de Mesquita Filho” – Faculdade de Ciências Agrárias e Veterinárias – Department of Veterinary Medicine and Surgery – Jaboticabal (São Paulo) – Brazil
| | - Bruno Watanabe Minto
- Universidade Estadual Paulista “Júlio de Mesquita Filho” – Faculdade de Ciências Agrárias e Veterinárias – Department of Veterinary Medicine and Surgery – Jaboticabal (São Paulo) – Brazil
| | | | - Caio Afonso dos Santos Malta
- Universidade Estadual Paulista “Júlio de Mesquita Filho” – Faculdade de Ciências Agrárias e Veterinárias – Department of Veterinary Medicine and Surgery – Jaboticabal (São Paulo) – Brazil
| | | | - Dayvid Vianêis Farias de Lucena
- Universidade Estadual Paulista “Júlio de Mesquita Filho” – Faculdade de Ciências Agrárias e Veterinárias – Department of Veterinary Medicine and Surgery – Jaboticabal (São Paulo) – Brazil
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Zhang Y, Song J, Lu Y, Yi M, Xu X, Ding L. A practical method for the retrieval of tulip-head polyaxial pedicle screw by reusing the rod in revision and implants removal surgery: introduction of technique and evaluation of clinical outcomes. BMC Surg 2023; 23:152. [PMID: 37280570 DOI: 10.1186/s12893-023-02063-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 05/31/2023] [Indexed: 06/08/2023] Open
Abstract
BACKGROUND The removal of spinal implants is needed in revision surgery or in some cases whose fracture had healed or fusion had occurred. The slip of polyaxial screw or mismatch of instruments would make this simple procedure intractable. Here we introduce a simple and practical method to address this clinical dilemma. METHODS This is a retrospective study. The patients underwent new technique for retrieving the implants from July 2019 to July 2022 were labeled as group A, while the patients underwent traditional implants retrieval technique from January 2017 to January 2020 were labeled as group B. Patients in each group were subdivided into revision surgery group (r group) and simple implants removal group (s group) according to the surgery fashion. For the new technique, the retrieved rod was cut off to a proper length which was matched with the size of tulip head, and was replaced into the tulip head. After tightened with nut, a monoaxial screw-rod "construct" was formed. Then the "construct" can be retrieved by a counter torque. The operation duration, intraoperative blood loss, post-operative bacteria culture, hospital stay and costs were analyzed. RESULTS A total of 116 polyaxial screws with difficult retrieval (43 screws in group A, 73 screws in group B) in 78 patients were recorded, in which 115 screws were successfully retrieved. Significant differences were found in the mean operation duration, intraoperative blood loss when comparing the r group in group A and B, as well as the s group in group A and B (P < 0.05). There were no significant differences in hospital stay and costs between group A and B. Three patients were found positive bacteria culture of drainage tube/tape in group A (3/30), while 7 patients in group B (7/48). The most prevalent bacteria was Propionibacterium acnes. CONCLUSION This technique is practical and safe in retrieving tulip head poly-axial screw. Reduced operation duration and intraoperative bloods loss may potentially alleviate the hospitalization burden of patients. Positive bacterial cultivation results are common after implants removal surgery, but they rarely represent an organized infection. A positive culture with P. acnes or S. epidermidis should be interpreted with caution.
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Affiliation(s)
- Yao Zhang
- Department of Spinal Surgery, Beijing Shijitan Hospital, Capital Medical University, No. 10, Tieyi Road, Yangfangdian street, Haidian District, Beijing, 10038, People's Republic of China
| | - Jipeng Song
- Department of Spinal Surgery, Beijing Shijitan Hospital, Capital Medical University, No. 10, Tieyi Road, Yangfangdian street, Haidian District, Beijing, 10038, People's Republic of China
| | - Yuzheng Lu
- Department of Spinal Surgery, Beijing Shijitan Hospital, Capital Medical University, No. 10, Tieyi Road, Yangfangdian street, Haidian District, Beijing, 10038, People's Republic of China
| | - Meng Yi
- Department of Spinal Surgery, Beijing Shijitan Hospital, Capital Medical University, No. 10, Tieyi Road, Yangfangdian street, Haidian District, Beijing, 10038, People's Republic of China
| | - Xiaohang Xu
- Department of Spinal Surgery, Yantai Affiliated Hospital of Binzhou Medical College, No. 717, Jinbu Street, Yantai, Shandong, 264000, People's Republic of China
| | - Lixiang Ding
- Department of Spinal Surgery, Beijing Shijitan Hospital, Capital Medical University, No. 10, Tieyi Road, Yangfangdian street, Haidian District, Beijing, 10038, People's Republic of China.
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Kumar N, Alathur Ramakrishnan S, Lopez KG, Wang N, Madhu S, Vellayappan BA, Tpd Hallinan J, Fuh JYH, Kumar AS. Design and 3D printing of novel titanium spine rods with lower flexural modulus and stiffness profile with optimised imaging compatibility. 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 2023; 32:1953-1965. [PMID: 37052651 DOI: 10.1007/s00586-023-07674-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Revised: 03/07/2023] [Accepted: 03/18/2023] [Indexed: 04/14/2023]
Abstract
PURPOSE To manufacture and test 3D printed novel design titanium spine rods with lower flexural modulus and stiffness compared to standard solid titanium rods for use in metastatic spine tumour surgery (MSTS) and osteoporosis. METHODS Novel design titanium spine rods were designed and 3D printed. Three-point bending test was performed to assess mechanical performance of rods, while a French bender was used to assess intraoperative rod contourability. Furthermore, 3D printed spine rods were tested for CT & MR imaging compatibility using phantom setup. RESULTS Different spine rod designs generated includes shell, voronoi, gyroid, diamond, weaire-phelan, kelvin, and star. Tests showed 3D printed rods had lower flexural modulus with reduction ranging from 2 to 25% versus standard rod. Shell rods exhibited highest reduction in flexural modulus of 25% (~ 77.4 GPa) and star rod exhibited lowest reduction in flexural modulus of 2% (100.8GPa). 3D printed rod showed reduction in stiffness ranging from 40 to 59%. Shell rod displayed highest reduction in stiffness of 59% (179.9 N/mm) and gyroid had least reduction in stiffness of 40% (~ 259.2 N/mm). Rod bending test showed that except gyroid, other rod designs demonstrated lesser bending difficulty versus standard rod. All 3D printed rods demonstrated improved CT/MR imaging compatibility with reduced artefacts versus standard rod. CONCLUSION By utilising novel design approach, we successfully generated a spine rod design portfolio with lower flexural modulus/stiffness profile and better CT/MR imaging compatibility for potential use in MSTS/other conditions such as osteoporosis. Thus, exploration of new rod designs in surgical application could enhance treatment outcome and improve quality of life for patients.
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Affiliation(s)
- Naresh Kumar
- Department of Orthopaedic Surgery, National University Health System, Level 11 Tower Block, 1E, Lower Kent Ridge Road, Singapore, 119228, Singapore.
| | - Sridharan Alathur Ramakrishnan
- Department of Orthopaedic Surgery, National University Health System, Level 11 Tower Block, 1E, Lower Kent Ridge Road, Singapore, 119228, Singapore
| | - Keith Gerard Lopez
- Department of Orthopaedic Surgery, National University Health System, Level 11 Tower Block, 1E, Lower Kent Ridge Road, Singapore, 119228, Singapore
| | - Niyou Wang
- Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Sirisha Madhu
- Department of Orthopaedic Surgery, National University Health System, Level 11 Tower Block, 1E, Lower Kent Ridge Road, Singapore, 119228, Singapore
| | - Balamurugan A Vellayappan
- Department of Radiation Oncology, National University Health System, Level 7 Tower Block, 1E, Lower Kent Ridge Road, Singapore, 119228, Singapore
| | - James Tpd Hallinan
- Department of Diagnostic Imaging, National University Hospital, Level 2 National University Hospital Main Building, 5 Lower Kent Ridge Rd, Singapore, 119074, Singapore
| | - Jerry Ying Hsi Fuh
- Department of Mechanical Engineering, National University of Singapore, #04-18 Block EA, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - A Senthil Kumar
- Department of Mechanical Engineering, National University of Singapore, #05-26 Block EA, 9 Engineering Drive 1, Singapore, 117575, Singapore
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Steinmetz MP, Riggleman JR, Mahoney JM, Harris JA, Butler JB, Ferrick BJ, Bucklen BS. A Dual-Screw Technique for Vertebral Compression Fractures via Robotic Navigation in the Osteopenic Lumbar Spine: An In-Vitro Biomechanical Analysis. Global Spine J 2023:21925682231152833. [PMID: 36644787 DOI: 10.1177/21925682231152833] [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] [Indexed: 01/17/2023] Open
Abstract
STUDY DESIGN Biomechanical cadaveric study. OBJECTIVES Multi-rod constructs maximize posterior fixation, but most use a single pedicle screw (PS) anchor point to support multiple rods. Robotic navigation allows for insertion of PS and cortical screw (CS) within the same pedicle, providing 4 points of bony fixation per vertebra. Recent studies demonstrated radiographic feasibility for dual-screw constructs for posterior lumbar spinal fixation; however, biomechanical characterization of this technique is lacking. METHODS Fourteen cadaveric lumbar specimens (L1-L5) were divided into 2 groups (n = 7): PS, and PS + CS. VCF was simulated at L3. Bilateral posterior screws were placed from L2-L4. Load control (±7.5Nm) testing performed in flexion-extension (FE), lateral bending (LB), axial rotation (AR) to measure ROM of: (1) intact; (2) 2-rod construct; (3) 4-rod construct. Static compression testing of 4-rod construct performed at 5 mm/min to measure failure load, axial stiffness. RESULTS Four-rod construct was more rigid than 2-rod in FE (P < .001), LB (P < .001), AR (P < .001). Screw technique had no significant effect on FE (P = .516), LB (P = .477), or AR (P = .452). PS + CS 4-rod construct was significantly more stable than PS group (P = .032). Stiffness of PS + CS group (445.8 ± 79.3 N/mm) was significantly greater (P = .019) than PS (317.8 ± 79.8 N/mm). Similarly, failure load of PS + CS group (1824.9 ± 352.2 N) was significantly greater (P = .001) than PS (913.4 ± 309.8 N). CONCLUSIONS Dual-screw, 4-rod construct may be more stable than traditional rod-to-rod connectors, especially in axial rotation. Axial stiffness and ultimate strength of 4-rod, dual-screw construct were significantly greater than rod-to-rod. In this study, 4-rod construct was found to have potential biomechanical benefits of increased strength, stiffness, stability.
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Affiliation(s)
- Michael P Steinmetz
- Department of Neurosurgery, Cleveland Clinic Lerner College of Medicine, Center for Spine Health Neurologic Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Jessica R Riggleman
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
| | - Jonathan M Mahoney
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
| | - Jonathan A Harris
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
| | - John B Butler
- Department of Neurosurgery, Cleveland Clinic Lerner College of Medicine, Center for Spine Health Neurologic Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Bryan J Ferrick
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, USA
| | - Brandon S Bucklen
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
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Oda Y, Takigawa T, Ito Y, Misawa H, Tetsunaga T, Uotani K, Ozaki T. Mechanical Study of Various Pedicle Screw Systems including Percutaneous Pedicle Screw in Trauma Treatment. MEDICINA (KAUNAS, LITHUANIA) 2022; 58:565. [PMID: 35629982 PMCID: PMC9143153 DOI: 10.3390/medicina58050565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Revised: 03/15/2022] [Accepted: 04/19/2022] [Indexed: 11/17/2022]
Abstract
Background and Objectives: Spine surgery using a percutaneous pedicle screw placement (PPSP) is widely implemented for spinal trauma. However, percutaneous systems have been reported to have weak screw-rod connections. In this study, conventional open and percutaneous systems were biomechanically evaluated and compared. Material and Methods: The experiments were performed in two stages: the first stage was a break test, whereas the second stage was a fatigue test. Four systems were used for the experiments. System 1 was intended for conventional open surgery (titanium rod with a 6.0 mm diameter, using a clamp connecting mechanism). System 2 was a percutaneous pedicle screw (PPS) system for trauma (titanium alloy rod with a 6.0 mm diameter, using ball ring connections). System 3 was a PPS system for trauma (cobalt-chromium alloy rod with a 6.0 mm diameter, using sagittal adjusting screw connections). System 4 was a general-purpose PPS system (titanium alloy rod with a 5.5 mm diameter, using a mechanism where the adapter in the head holds down the screw). Results: Stiffness values of 54.8 N/mm, 43.1 N/mm, 90.9 N/mm, and 39.3 N/mm were reported for systems 1, 2, 3, and 4, respectively. The average number of load cycles in the fatigue test was 134,393, 40,980, 1,550,389, and 147,724 for systems 1 to 4, respectively. At the end of the test, the displacements were 0.2 mm, 16.9 mm, 1.2 mm, and 8.6 mm, respectively. System 1, with a locking mechanism, showed the least displacement at the end of the test. Conclusion: A few PPS systems showed better results in terms on stiffness and life than the open system. The experiments showed that mechanical strength varies depending on the spinal implant. The experiments conducted are essential and significant to provide the mechanical strength required for surgical reconstruction.
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Affiliation(s)
- Yoshiaki Oda
- Department of Orthopaedic Surgery, Okayama University Hospital, 2-5-1 Shikata-cho, Kitaku, Okayama City 700-8558, Japan; (H.M.); (T.T.); (K.U.)
| | - Tomoyuki Takigawa
- Department of Orthopaedic Surgery, Kobe Red Cross Hospital, 1-3-1 Wakinohamakaigandori, Chuoku, Kobe City 651-0073, Japan; (T.T.); (Y.I.)
| | - Yasuo Ito
- Department of Orthopaedic Surgery, Kobe Red Cross Hospital, 1-3-1 Wakinohamakaigandori, Chuoku, Kobe City 651-0073, Japan; (T.T.); (Y.I.)
| | - Haruo Misawa
- Department of Orthopaedic Surgery, Okayama University Hospital, 2-5-1 Shikata-cho, Kitaku, Okayama City 700-8558, Japan; (H.M.); (T.T.); (K.U.)
| | - Tomoko Tetsunaga
- Department of Orthopaedic Surgery, Okayama University Hospital, 2-5-1 Shikata-cho, Kitaku, Okayama City 700-8558, Japan; (H.M.); (T.T.); (K.U.)
| | - Koji Uotani
- Department of Orthopaedic Surgery, Okayama University Hospital, 2-5-1 Shikata-cho, Kitaku, Okayama City 700-8558, Japan; (H.M.); (T.T.); (K.U.)
| | - Toshifumi Ozaki
- Department of Orthopaedic Surgery, Dentistry, and Pharmaceutical Sciences, Graduate School of Medicine, Okayama University, 2-5-1 Shikata-cho, Kitaku, Okayama City 700-8558, Japan;
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Comparison of the biomechanical performance of three spinal implants for treating the wedge-shaped burst fractures. MEDICINE IN NOVEL TECHNOLOGY AND DEVICES 2022. [DOI: 10.1016/j.medntd.2021.100109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Lee SJ, Lee JH, Lee HJ, Oh JW, Park IH. Pullout strength of pedicle screws using cadaveric vertebrae with or without artificial demineralization. Spine J 2021; 21:1580-1586. [PMID: 33872804 DOI: 10.1016/j.spinee.2021.04.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 04/07/2021] [Accepted: 04/08/2021] [Indexed: 02/03/2023]
Abstract
OBJECTIVES To evaluate the differences in the pullout strength and displacement of pedicle screws in cadaveric thoracolumbar vertebrae with or without artificial demineralization. METHODS Five human lumbar and five thoracic vertebrae from one cadaver were divided into two hemivertebrae. The left-side specimens were included in the simulated osteopenic model group and the right-side bones in a control group. In the model group, we immersed each specimen in HCl (1 N) solution for 40 minutes. We measured bone mineral density (BMD) using dual-energy X-ray absorptiometry and quantitative computerized tomography. We inserted polyaxial pedicle screws into the 20 pedicles of the cadaveric lumbar and thoracic spine after measuring the BMD of the 2 hemivertebrae of each specimen. We measured the pullout strength and displacement of the screws before failure in each specimen using an Instron system. RESULTS The average pullout strength of the simulated osteopenic model group was 76% that of the control group. In the control and model groups, the pullout strength was 1678.87±358.96 N and 1283.83±341.97 N, respectively, and the displacement was 2.07±0.34 mm and 2.65±0.50 mm, respectively (p<.05). We detected positive correlations between pullout strength and BMD in the control group and observed a negative correlation between displacement and BMD in the model group. CONCLUSIONS By providing an anatomically symmetric counterpart, the human cadaveric model with or without demineralization can be used as a test bed for pullout tests of the spine. In the simulated osteopenic model group, pullout strength was significantly decreased compared with the untreated control group. CLINICAL SIGNIFICANCE Decreased bone mineral density may significantly reduce the pullout strength of a pedicle screw, even though the range is osteopenic rather than osoteoporotic.
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Affiliation(s)
- Suk-Joong Lee
- Department of Orthopaedic Surgery, Gyeongsang National University School of Medicine and Gyeongsang National University Changwon Hospital, Changwon, Republic of Korea
| | - Jin-Han Lee
- Department of Orthopaedic Surgery, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea
| | - Hyun-Joo Lee
- Department of Orthopaedic Surgery, School of Medicine, Kyungpook National University, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea; Department of Orthopaedic Surgery, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea
| | - Ji Won Oh
- Department of Anatomy, School of Medicine, Kyungpook National University, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea; Biomedical Research Institute, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea
| | - Il-Hyung Park
- Department of Orthopaedic Surgery, School of Medicine, Kyungpook National University, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea; Department of Orthopaedic Surgery, Kyungpook National University Hospital, 130 Dongduk-ro, Jung-gu, Daegu, Republic of Korea.
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Peck JH, Cadel E, Palepu V, Ferrell BM, Warner CH. Mechanical performance of thoracolumbosacral pedicle screw systems: An analysis of data submitted to the Food and Drug Administration. J Biomech 2021; 125:110551. [PMID: 34182324 DOI: 10.1016/j.jbiomech.2021.110551] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Revised: 05/24/2021] [Accepted: 05/31/2021] [Indexed: 11/18/2022]
Abstract
Thoracolumbosacral pedicle screw systems (TPSSs) are spinal implants commonly utilized to stabilize the spine as an adjunct to fusion for a variety of spinal pathologies. These systems consist of components including pedicle screws, rods, hooks, and various connectors that allow the surgeon to create constructs that can be affixed to a wide range of spinal anatomy. During the development and regulatory clearance process, TPSSs are subjected to mechanical testing such as static and dynamic compression bending per ASTM F1717, axial and torsional grip testing per ASTM F1798, and foam block pullout testing per ASTM F543. In this study, design and mechanical testing data were collected from 200 premarket notification (510(k)) submissions for TPSSs submitted to FDA between 2007 and 2018. Data were aggregated for the most commonly performed mechanical tests, and analyses were conducted to assess differences in performance based on factors such as component type, dimensions, and materials of construction. Rod material had a significant impact on construct stiffness in static compression bending testing with cobalt chromium rods being significantly stiffer than titanium rods of the same diameter. Pedicle screw type had an impact on compression bending yield strength with monoaxial screws having significantly higher yield strength as compared to polyaxial or uniplanar screws. Axial and torsional gripping capacities between components and the rods were significantly lower for cross-connectors than the other component types. The aggregated data presented here can be utilized for comparative purposes to aid in the development of future TPSSs.
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Affiliation(s)
- Jonathan H Peck
- U.S. Food and Drug Administration, Center for Devices and Radiological Health, Office of Product Evaluation and Quality, Office of Orthopedic Devices, Silver Spring, MD 20993, USA.
| | - Eileen Cadel
- U.S. Food and Drug Administration, Center for Devices and Radiological Health, Office of Product Evaluation and Quality, Office of Orthopedic Devices, Silver Spring, MD 20993, USA
| | - Vivek Palepu
- U.S. Food and Drug Administration, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Division of Applied Mechanics, Silver Spring, MD 20993, USA
| | - Brittany M Ferrell
- U.S. Food and Drug Administration, Center for Devices and Radiological Health, Office of Product Evaluation and Quality, Office of Orthopedic Devices, Silver Spring, MD 20993, USA
| | - Charles H Warner
- U.S. Food and Drug Administration, Center for Devices and Radiological Health, Office of Product Evaluation and Quality, Office of Orthopedic Devices, Silver Spring, MD 20993, USA
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Yao W, Zhou T, Huang K, Dai M, Mo F, Xu J, Cao Z, Lai Q, Xie B, Guo R, Zhang B. A comparison of monoaxial pedicle screw versus polyaxial pedicle screw in short-segment posterior fixation for the treatment of thoracolumbar fractured vertebra. ANNALS OF TRANSLATIONAL MEDICINE 2021; 9:669. [PMID: 33987367 PMCID: PMC8106060 DOI: 10.21037/atm-21-881] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Background Posterior pedicle screw fixation had been applied to maintain spinal stability and avoid further nerve damage in thoracolumbar fracture. This study aimed to evaluate the efficacy of short-segment posterior fixation with monoaxial pedicle screws versus polyaxial pedicle screws in treating thoracolumbar fracture. Methods A total of 75 patients with thoracolumbar fracture who underwent short-segment posterior fixation with monoaxial pedicle screw (group A) or polyaxial pedicle screw (group B) were retrospectively enrolled. The patient demographic and radiological data were analyzed between the two groups. Results A total of 63 patients with an average age of 44.7±11.5 years were finally recruited in this study. There were no significant differences in age, gender, fracture level, thoracolumbar injury classification and severity scale (TLISS) score, American Spinal Injury Association (ASIA) score, Arbeitsgemeinschaft für Osteosynthesefragen (AO) classification, and hospital stay between the two groups (P>0.05). At the last follow-up, the prevertebral height ratio and normal-to-injured vertebral height ratio were significantly decreased in group A compared to group B (P=0.027 and P=0.007, respectively). Conclusions Short-segment posterior fixation with monoaxial or polyaxial pedicle screw for fractured thoracolumbar vertebra can restore injured vertebral height. Compared with polyaxial pedicle screw, monoaxial pedicle screw endows stronger leverage which is more beneficial for restoring injured vertebral height and recovery of the damaged endplate in thoracolumbar short-segment posterior fixation.
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Affiliation(s)
- Wenye Yao
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Tonghua Zhou
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Kai Huang
- Department of Orthopedics, Zhabei Central Hospital of Jing'an District, Shanghai, China
| | - Min Dai
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Fengbo Mo
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Jing Xu
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Zhiyou Cao
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Qi Lai
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Banglin Xie
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Runsheng Guo
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
| | - Bin Zhang
- Department of Orthopaedics, The First Affiliated Hospital of Nanchang University, Nanchang, China
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11
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Perna A, Santagada DA, Bocchi MB, Zirio G, Proietti L, Tamburrelli FC, Genitiempo M. Early loss of angular kyphosis correction in patients with thoracolumbar vertebral burst (A3-A4) fractures who underwent percutaneous pedicle screws fixation. J Orthop 2021; 24:77-81. [PMID: 33679031 DOI: 10.1016/j.jor.2021.02.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 12/28/2020] [Accepted: 02/14/2021] [Indexed: 11/16/2022] Open
Abstract
Purpose Percutaneous trans-pedicle screws represent a surgical option frequently performed in patients affected by thoracolumbar vertebral burst fractures (A3-A4). The aim of the study was to evaluate the early loss of kyphosis correction and its clinical correlations in a cohort of patients affected by burst spinal fracture treated with percutaneous trans-pedicle screws fixation. Methods The present investigation consists in a retrospective one center analysis. The primary outcome was the evaluation of the early loss of correction. Secondary outcomes were the bi-segmental kyphosis change, the clinical outcome and the correlation between clinical outcome and the loss of correction. Results Among 435 patients 97 were included in the study. A mean 3.3° of early loss of correction was observed between postoperative and 1 month follow-up evaluations. The mean anterior vertebral body height change was 3.8 mm. No statistical differences were found in clinical and functional outcomes between patients with >2° or <2° of kyphosis loss of correction. Conclusion No statistical differences were found between 1 e 6 months postoperative kyphosis loss of correction. The amount of loss of correction seems not to influence clinical outcomes after percutaneous trans-pedicle screw fixation in patients with vertebral burst fractures.
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Affiliation(s)
- Andrea Perna
- Istituto di Clinica Ortopedica, Fondazione Policlinico Universitario A. Gemelli, Catholic University, Rome, Italy
| | | | - Maria Beatrice Bocchi
- Istituto di Clinica Ortopedica, Fondazione Policlinico Universitario A. Gemelli, Catholic University, Rome, Italy
| | - Gianfranco Zirio
- Istituto di Clinica Ortopedica, Fondazione Policlinico Universitario A. Gemelli, Catholic University, Rome, Italy
| | - Luca Proietti
- Istituto di Clinica Ortopedica, Fondazione Policlinico Universitario A. Gemelli, Catholic University, Rome, Italy.,Istituto di Clinica Ortopedica, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Francesco Ciro Tamburrelli
- Istituto di Clinica Ortopedica, Fondazione Policlinico Universitario A. Gemelli, Catholic University, Rome, Italy.,Istituto di Clinica Ortopedica, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Maurizio Genitiempo
- Istituto di Clinica Ortopedica, Fondazione Policlinico Universitario A. Gemelli, Catholic University, Rome, Italy
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12
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Partial Threading of Pedicle Screws in a Standard Construct Increases Fatigue Life: A Biomechanical Analysis. APPLIED SCIENCES-BASEL 2021. [DOI: 10.3390/app11041503] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
This study proposed a pedicle screw design where the proximal 1/3 of the screw is unthreaded to improve fixation in posterior spinal surgery. This design was also expected to reduce the incidence of mechanical failure often observed when an unsupported screw length is exposed outside the vertebra in deformed or degenerated segments. The aim of this study was to evaluate the fatigue life of the novel pedicle screw design using finite element analysis and mechanical testing in a synthetic spinal construct in accordance with American Society for Testing and Materials (ASTM) F1717. The following setups were evaluated: (i) pedicle screw fully inserted into the test block (EXP-FT-01 and EXP-PU-01; full thread (FT), proximal unthread (PU)) and (ii) pedicle screw inserted but leaving an exposed shaft length of 7.6 mm (EXP-FT-02 and EXP-PU-02). Corresponding finite element models FEM-FT-01, FEM-FT-02, FEM-PU-01, and FEM-PU-02 were also constructed and subjected to the same loading conditions as the experimental groups. The results showed that under a 220 N axial load, the EXP-PU-01 group survived the full 5 million cycles, the EXP-PU-02 group failed at 4.4 million cycles on average, and both EXP-FT-01 and EXP-FT-02 groups failed after less than 1.0 million cycles on average, while the fatigue strength of the EXP-FT-02 group was the lowest at 170 N. The EXP-FT-01 and EXP-FT-02 constructs failed through fracture of the pedicle screw, but a rod fractured in the EXP-PU-02 group. In comparison to the FEM-FT-01 model, the maximum von Mises stress on the pedicle screw in the FEM-PU-01 and FEM-PU-02 models decreased by −43% and −27%, respectively. In conclusion, this study showed that having the proximal 1/3 of the pedicle screw unthreaded can reduce the risk of screw fatigue failure when used in deformed or degenerated segments.
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Kim KD, Panchal R, Moldavsky M, Wang W, Bucklen BS. Effects of pre-contoured and in situ contoured rods on the mechanical strength and durability of posterior cervical instrumentation: a finite-element analysis and scanning electron microscopy investigation. Spine Deform 2020; 8:569-576. [PMID: 32430793 DOI: 10.1007/s43390-020-00078-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Accepted: 12/18/2019] [Indexed: 12/01/2022]
Abstract
STUDY DESIGN Finite-element analysis. OBJECTIVES Intraoperative contouring of rods is a common procedure for spine surgeons to match the native curvature of the spine, but it may lead to premature weakening of the rod. This study investigated the effect of different bending methods on rod fatigue performance. Rod failure in the cervical spine is of clinical concern, particularly when spanning the cervicothoracic region and when considering corrective osteotomies for deformity correction and global spinal alignment. METHODS Finite-element models were developed to simulate rod bending (3.5 mm D, 40 mm L) to achieve a 23° angle with 3 different bending methods: French single, multiple bending, and in situ bending. Simulations were conducted in 4 steps: rod bending, rod spring back, residual stress relaxation, and F1717 mechanical test simulation. RESULTS French single bending resulted in the highest residual stress concentrations for both titanium (TiAlV) and cobalt chrome (CoCr) at 783 MPa and 507 MPa, respectively. During F1717 test simulation, the French single bent rod had its highest tensile stress in the middle, with 917 MPa and 623 MPa, respectively, for TiAlV and CoCr, compared to in situ (580 MPa and 586 MPa for TiAlV and CoCr) and the French multiple bent rod (765 MPa and 619 MPa for TiAlV and CoCr). The computational model found that CoCr rods made the construct least prone to deformation. CONCLUSIONS French single bend with TiAlV rods put the construct at highest risk of failure. CoCr rods led to minimal physical changes in microstructure while showing evidence of flattening.
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Affiliation(s)
- Kee D Kim
- UC Davis Medical Center, UC Davis School of Medicine, 4860 Y Street, Suite 3740, Sacramento, CA, 95817, USA
| | - Ripul Panchal
- American Neurospine Institute, PLLC 4001 West 15th Street, Suite 445, Plano, TX, 75093-5845, USA
| | - Mark Moldavsky
- Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., 2560 General Armistead Avenue, Audubon, PA, 19403, USA
| | - Wenhai Wang
- Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., 2560 General Armistead Avenue, Audubon, PA, 19403, USA.
| | - Brandon S Bucklen
- Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., 2560 General Armistead Avenue, Audubon, PA, 19403, USA
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A Novel Spine Fixation System Made Entirely of Carbon-Fiber-Reinforced PEEK Composite: An In Vitro Mechanical Evaluation. Adv Orthop 2020; 2020:4796136. [PMID: 32566313 PMCID: PMC7301173 DOI: 10.1155/2020/4796136] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Revised: 03/31/2020] [Accepted: 04/27/2020] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Semirigid spine fixation systems utilizing nonmetallic materials have emerged as a promising innovation to overcome the inherent disadvantages of metal instrumentation in spine surgery. This study tests the mechanical properties of a novel spine fixation system made entirely of carbon-fiber-reinforced PEEK (CFR-PEEK) composite material (CarboClear System, CarboFix Orthopedics Ltd., Israel). METHODS An in vitro mechanical evaluation of the CFR-PEEK CarboClear system was conducted in compliance with the American Society for Testing and Materials (ASTM) F1717, F2193, and F543 standards. RESULTS The mean bending yield load, bending ultimate load, and bending stiffness of the construct were 322 N, 363 N, and 45 N/mm, respectively. All tested samples completed 5 × 106 dynamic cycles successfully, with no evidence of fatigue failure at increasing load levels, up to 83% of ultimate bending load. The mean torsional stiffness was 1.0 Nm/deg and the mean screw axial pull-out strength was 2,037 N. CONCLUSION The CarboClear Pedicle Screw System has mechanical properties comparable to those of other commonly used titanium-made systems, with superior fatigue properties. The fatigue resistance, modulus of elasticity which is very similar to that of bone, radiolucency, and CT/MRI artifact-free feature of this spine fixation system made entirely of CFR-PEEK may offer advantages over traditional spine fixation systems made of metal alloys.
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15
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Starlinger J, Lorenz G, Fochtmann-Frana A, Sarahrudi K. Bisegmental posterior stabilisation of thoracolumbar fractures with polyaxial pedicle screws: Does additional balloon kyphoplasty retain vertebral height? PLoS One 2020; 15:e0233240. [PMID: 32421734 PMCID: PMC7233542 DOI: 10.1371/journal.pone.0233240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Accepted: 04/30/2020] [Indexed: 11/18/2022] Open
Abstract
We retrospectively evaluated single-level compression fractures (T12-L3) scheduled for a short-segment POS (posterior-only stabilization) using polyaxial screws. Patients averaged 55.7 years (range, 19–65). Patients received either POS or, concomitantly, BK (balloon kyphoplasty) of the fractured vertebrae as well. Primary endpoint was the radiological outcome at the last radiographic follow-up prior to implant removal. POS together with BK of the fractured vertebrae resulted in a significant improvement of the local kyphosis angle and vertebral body compression rates immediately post-OP. During the further course of FU, a considerable loss of correction was observed post-OP in both groups. (Local KA: pre-OP/ post-OP/ FU: 12.6±4.8/ 3.35±4.8/ 11.6±6.0; anterior vertebral body compression%: pre-OP/post-OP/ FU: 71.94±12.3/ 94.78±19.95/ 78.17±14.74). VAS was significantly improved from 7.2±1.3 pre-OP to 2.7±1.3 (P<0.001) at FU. We found a significant restoration of the vertebral body height by BK. Nevertheless, follow-up revealed a noticeable loss of reduction. Given the fact that BK used together with polyaxial screws did not maintain intra-operative reduction, our data do not support this additional maneuver when used together with bi-segmental polyaxial pedicle screw fixation.
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Affiliation(s)
- Julia Starlinger
- Department for Orthopedics, Mayo Clinic, Rochester, MN, United States of America
- Department for Orthopedics and Trauma Surgery, Medical University Vienna, Vienna, Austria
- * E-mail:
| | | | | | - Kambiz Sarahrudi
- Department for Trauma Surgery, Landesklinikum Wiener Neustadt, Wiener Neustadt, Austria
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16
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Liu PY, Lai PL, Lin CL. A biomechanical investigation of the retentive force of pedicle screw structures for different screw tulip designs. Clin Biomech (Bristol, Avon) 2019; 70:23-30. [PMID: 31382200 DOI: 10.1016/j.clinbiomech.2019.06.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2018] [Revised: 05/28/2019] [Accepted: 06/04/2019] [Indexed: 02/07/2023]
Abstract
BACKGROUND Pedicle screw based spinal fixation systems have been widely used for treating a variety of spinal diseases. The retentive force is an important factor that determines structural stability. The screw tulip design and the magnitude of nut tightening torque influence the retentive force. This study investigated the influences of varied tilt angles between the shaft-rod interface and varied nut tightening torques on the retentive force of the monoaxial, polyaxial, and uniplanar screws. METHODS Three types of tulip constructs were biomechanically tested. Two parameters that affect the retentive force include the tilt angle and the nut tightening torque. The retentive force was investigated by an axial gripping capacity test and axial torque gripping capacity test. FINDING Among all combinations of screw designs and tilt angles, the 12 Nm nut tightening torque offered a greater retentive force than the 8 Nm, except for monoaxial screws with a 0 degree tilt angle. For monoaxial screws, the retentive force was negatively correlated with increasing tilt angles. For polyaxial and uniplanar screws, the retentive forces remained constant with increasing tilt angles. INTERPRETATION In monoaxial screws, when the axis of the shaft isn't perpendicular to the axis of the rod, a gap is formed between the tulip-rod interface. This results in a decreased retentive force. In polyaxial and uniplanar screws, the contact surfaces were the same in different tilt angles, therefore, the retentive force remained constant, which was attributed to the adjustable tulips always being perpendicular to the axis of the rods.
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Affiliation(s)
- Po-Yi Liu
- Department of Biomedical Engineering, National Yang-Ming University, No.155, Sec. 2, Linong St., Beitou Dist., Taipei City 11221, Taiwan; Department of Orthopedic Surgery, Bone and Joint Research Center, Chang Gung Memorial Hospital at Linkou, College of Medicine, Chang Gung University, No. 5, Fuxing St., Guishan Dist., Taoyuan City 33305, Taiwan
| | - Po-Liang Lai
- Department of Orthopedic Surgery, Bone and Joint Research Center, Chang Gung Memorial Hospital at Linkou, College of Medicine, Chang Gung University, No. 5, Fuxing St., Guishan Dist., Taoyuan City 33305, Taiwan.
| | - Chun-Li Lin
- Department of Biomedical Engineering, National Yang-Ming University, No.155, Sec. 2, Linong St., Beitou Dist., Taipei City 11221, Taiwan.
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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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Mechanical Performance of Posterior Spinal Instrumentation and Growing Rod Implants: Experimental and Computational Study. Spine (Phila Pa 1976) 2019; 44:1270-1278. [PMID: 30994599 PMCID: PMC6722018 DOI: 10.1097/brs.0000000000003061] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN Experimental and computational study of posterior spinal instrumentation and growing rod constructs per ASTM F1717-15 vertebrectomy methodology for static compressive bending. OBJECTIVE Assess mechanical performance of standard fusion instrumentation and growing rod constructs. SUMMARY OF BACKGROUND DATA Growing rod instrumentation utilizes fewer anchors and spans longer distances, increasing shared implant loads relative to fusion. There is a need to evaluate growing rod's mechanical performance. ASTM F1717-15 standard assesses performance of spinal instrumentation; however, effects of growing rods with side-by-side connectors have not been evaluated. METHODS Standard and growing rod constructs were tested per ASTM F1717-15 methodology; setup was modified for growing rod constructs to allow for connector offset. Three experimental groups (standard with active length 76 mm, and growing rods with active lengths 76 and 376 mm; n = 5/group) were tested; stiffness, yield load, and load at maximum displacement were calculated. Computational models were developed and used to locate stress concentrations. RESULTS For both constructs at 76 mm active length, growing rod stiffness (49 ± 0.8 N/mm) was significantly greater than standard (43 ± 0.4 N/mm); both were greater than growing rods at 376 mm (10 ± 0.3 N/mm). No significant difference in yield load was observed between growing rods (522 ± 12 N) and standard (457 ± 19 N) constructs of 76 mm. Growing rod constructs significantly decreased from 76 mm (522 ± 12 N) to 376 mm active length (200 ± 2 N). Maximum load of growing rods at 76 mm (1084 ± 11 N) was significantly greater than standard at 76 mm (1007 ± 7 N) and growing rods at 376 mm active length (392 ± 5 N). Simulations with active length of 76 mm were within 10% of experimental mechanical characteristics; stress concentrations were at the apex and cranial to connector-rod interaction for standard and growing rod models, respectively. CONCLUSION Growing rod constructs are stronger and stiffer than spinal instrumentation constructs; with an increased length accompanied a decrease in strength. Growing rod construct stress concentration locations observed during computational simulation are consistent with clinically observed failure locations. LEVEL OF EVIDENCE 5.
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Zhang Y, Sun MJ. Intelligently Taking Out Universal Screws and Nail Caps After Spine Internal Fixation. Orthop Surg 2019; 11:903-905. [PMID: 31429519 PMCID: PMC6819187 DOI: 10.1111/os.12488] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 09/13/2018] [Accepted: 10/31/2018] [Indexed: 11/30/2022] Open
Abstract
The purpose of this study was to present a surgical technique for taking out universal screw and nail caps which were difficult to removed. We used a variety of industrial hex wrenches, dental drills, and other equipment to take out internal hex nuts with different specifications (32 pieces) and universal screws (15 pieces) in 28 patients. A total of 32 nuts were taken out, 3 of which were polished by the industrial drill. A total of 17 were spun by hand, 2 were spun by locking pliers, 10 were turned by “I” type screwdriver, and 3 were turned by bone blade. A total of 15 screws were taken out, 9 of which were removed with a wrench and the other 6 by means of locking pliers after re‐fixing with a truncated titanium rod. The novel technique is simple and provides a solution following failure of a supporting device.
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Affiliation(s)
- Ye Zhang
- Department of Orthopaedics, 313rd Hospital of People's Liberation Army, Huludao, Liaoning, China
| | - Ming-Ju Sun
- Department of Orthopaedics, 313rd Hospital of People's Liberation Army, Huludao, Liaoning, China
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Kovacı H, Yetim AF, Çelik A. Biomechanical analysis of spinal implants with different rod diameters under static and fatigue loads: an experimental study. BIOMED ENG-BIOMED TE 2019; 64:339-346. [PMID: 29935109 DOI: 10.1515/bmt-2017-0236] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 06/01/2018] [Indexed: 02/06/2023]
Abstract
Spinal implants are commonly used in the treatment of spinal disorders or injuries. However, the biomechanical analyses of them are rarely investigated in terms of both biomechanical and clinical perspectives. Therefore, the main purpose of this study is to investigate the effects of rod diameter on the biomechanical behavior of spinal implants and to make a comparison among them. For this purpose, three spinal implants composed of pedicle screws, setscrews and rods, which were manufactured from Ti6Al4V, with diameters of 5.5 mm, 6 mm and 6.35 mm were used and a bilateral vertebrectomy model was applied to spinal systems. Then, the obtained spinal systems were tested under static tension-compression and fatigue (dynamic compression) conditions. Also, failure analyses were performed to investigate the fatigue behavior of spinal implants. After static tension-compression and fatigue tests, it was found that the yield loads, stiffness values, load carrying capacities and fatigue performances of spinal implants enhanced with increasing spinal rod diameter. In comparison to spinal implants with 5.5 mm rods, the fatigue limits of implants showed 13% and 33% improvements in spinal implants having 6 mm and 6.35 mm rods, respectively. The highest static and fatigue test results were obtained from spinal implants having 6.35 mm rods among the tested implants. Also, it was observed that the increasing yield load and stiffness values caused an increase in the fatigue limits of spinal implants.
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Affiliation(s)
- Halim Kovacı
- Department of Mechanical Engineering, Engineering Faculty, Atatürk University, Erzurum 25240, Turkey
| | - Ali Fatih Yetim
- Department of Mechanical Engineering, Engineering and Architecture Faculty, Erzurum Technical University, Erzurum 25700, Turkey
| | - Ayhan Çelik
- Department of Mechanical Engineering, Engineering Faculty, Atatürk University, Erzurum 25240, Turkey
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Liu H, Wang H, Liu J, Li C, Zhou Y, Xiang L. Biomechanical comparison of posterior intermediate screw fixation techniques with hybrid monoaxial and polyaxial pedicle screws in the treatment of thoracolumbar burst fracture: a finite element study. J Orthop Surg Res 2019; 14:122. [PMID: 31068193 PMCID: PMC6505109 DOI: 10.1186/s13018-019-1149-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 04/10/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND To compare the biomechanical characteristics of different posterior intermediate screw fixation techniques (ISFTs) with hybrid monoaxial pedicle screws (Mps) and polyaxial pedicle screws (Pps) used in thoracolumbar burst fractures. METHODS Fixation techniques are compared with regard to the von Mises stress (VMS) of the instrumentations and intradiscal pressures (IDPs) of the adjacent segments by finite element method (FEM). RESULTS The redistributed ROM of the fixation models with Pps fixed at the lowest segment was twice of the other fixation models in flexion and extension. The largest value of maximal VMS of a pedicle screw was located at the lowest pedicle screws when Mps are fixed at the lowest segment. The largest value of maximal VMS of the rods was decreased when more Pps are fixed at the models. Maximal IDPs of the upper adjacent segments were all larger than those of the lower adjacent segments. The maximal IDPs of the fixation model with MPs fixed at the lowest segment were larger than the other fixation models in flexion and extension. CONCLUSIONS Polyaxial pedicle screws could be placed at the upper or the median segment for the facilitated efficient application of the connecting rod. We should focus on the adjacent segmental degeneration especially the upper adjacent segment in the fixation model with Mps fixed at the lowest segment.
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Affiliation(s)
- Huan Liu
- Department of Orthopedics, Affiliated Traditional Chinese Medicine Hospital, Southwest Medical University, Luzhou, 646000, China
| | - Hongwei Wang
- Department of Orthopedics, General Hospital of Northern Theater Command of Chinese PLA, Shenyang, 110016, Liaoning, China. .,State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Science, Shenyang, 110016, Liaoning, China. .,State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan, 430074, Hubei, China. .,State Key Laboratory of Trauma, Burn and Combined Injury, The Third Military Medical University, Chongqing, 400038, China.
| | - Jun Liu
- Department of Orthopedics, General Hospital of Northern Theater Command of Chinese PLA, Shenyang, 110016, Liaoning, China
| | - Changqing Li
- Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, 400037, China
| | - Yue Zhou
- Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, 400037, China
| | - Liangbi Xiang
- Department of Orthopedics, General Hospital of Northern Theater Command of Chinese PLA, Shenyang, 110016, Liaoning, China
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Hitchon PW, Mahoney JM, Harris JA, Hussain MM, Klocke NF, Hao JC, Drazin D, Bucklen BS. Biomechanical evaluation of traditional posterior versus anterior spondylolisthesis reduction in a cadaveric grade I slip model. J Neurosurg Spine 2019; 31:246-254. [PMID: 31051462 DOI: 10.3171/2019.2.spine18726] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Accepted: 02/25/2019] [Indexed: 11/06/2022]
Abstract
OBJECTIVE Posterior reduction with pedicle screws is often used for stabilization of unstable spondylolisthesis to directly reduce misalignment or protect against micromotion while fusion of the affected level occurs. Optimal treatment of spondylolisthesis combines consistent reduction with a reduced risk of construct failure. The authors compared the reduction achieved with a novel anterior integrated spacer with a built-in reduction mechanism (ISR) to the reduction achieved with pedicle screws alone, or in combination with an anterior lumbar interbody fusion (ALIF) spacer, in a cadaveric grade I spondylolisthesis model. METHODS Grade I slip was modeled in 6 cadaveric L5-S1 segments by creation of a partial nucleotomy and facetectomy and application of dynamic cyclic loading. Following the creation of spondylolisthesis, reduction was performed under increasing axial loads, simulating muscle trunk forces between 50 and 157.5 lbs, in the following order: bilateral pedicle screws (BPS), BPS with an anterior spacer (BPS+S), and ISR. Percent reduction and reduction failure load-the axial load at which successful reduction (≥ 50% correction) was not achieved-were recorded along with the failure mechanism. Corrections were evaluated using lateral fluoroscopic images. RESULTS The average loads at which BPS and BPS+S failed were 92.5 ± 6.1 and 94.2 ± 13.9 lbs, respectively. The ISR construct failed at a statistically higher load of 140.0 ± 27.1 lbs. Reduction at the largest axial load (157.5 lbs) by the ISR device was tested in 67% (4 of 6) of the specimens, was successful in 33% (2 of 6), and achieved 68.3 ± 37.4% of the available reduction. For the BPS and BPS+S constructs, the largest axial load was 105.0 lbs, with average reductions of 21.3 ± 0.0% (1 of 6) and 32.4 ± 5.7% (3 of 6) respectively. CONCLUSIONS While both posterior and anterior reduction devices maintained reduction under gravimetric loading, the reduction capacity of the novel anterior ISR device was more effective at greater loads than traditional pedicle screw techniques. Full correction was achieved with pedicle screws, with or without ALIF, but under significantly lower axial loads. The anterior ISR may prove useful when higher reduction forces are required; however, additional clinical studies will be needed to evaluate the effectiveness of anterior devices with built-in reduction mechanisms.
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Affiliation(s)
| | - Jonathan M Mahoney
- 2Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, Pennsylvania
| | - Jonathan A Harris
- 2Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, Pennsylvania
| | - Mir M Hussain
- 2Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, Pennsylvania
| | - Noelle F Klocke
- 2Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, Pennsylvania
| | - John C Hao
- 3School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania; and
| | - Doniel Drazin
- 4Evergreen Hospital Neuroscience Institute, Kirkland, Washington
| | - Brandon S Bucklen
- 2Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, Pennsylvania
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Arnin U, El-Hawary R, Betz RR, Lonner BS, Floman Y. Preclinical Bench Testing on a Novel Posterior Dynamic Deformity Correction Device for Scoliosis. Spine Deform 2019; 7:203-212. [PMID: 30660213 DOI: 10.1016/j.jspd.2018.08.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Revised: 08/07/2018] [Accepted: 08/19/2018] [Indexed: 10/27/2022]
Abstract
STUDY DESIGN Biomechanical test. OBJECTIVE To summarize the preclinical tests performed to assess the durability of a novel fusionless dynamic device for the treatment of adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA The minimal invasive deformity correction (MID-C) system is a distractible posterior dynamic deformity correction device designed to reduce scoliosis for AIS patients, to maintain curve correction, and to preserve spinal motion. To overcome the challenges of wear and fatigue of this procedure, the system has two unique features: polyaxial joints at the rod-screw interface and a ceramic coating of the moving parts. METHODS Five biomechanical tests were performed: Static compression to failure, fatigue loading per ASTM F 1717 with 5.5-mm screws for 10 million cycles (MC) at 5 Hz, wear assessment, wear test of the polyaxial joint under 100 N load for 10 MC, and wear particle implantation in rabbits. RESULTS The system failed through buckling of the rod with loads over 3000 N (400% of human body weight). Dynamically, the system maintained 700 N for 10 MC with 5.5 mm screws. The maximum total steady-state wear rate was 0.074 mg/MC (0.03 per polyaxial joint and 0.014 mg/MC for the ratchet mechanism). Histologic evaluation of the particle injection sites indicated no difference in the local tissue response between the control and test articles. At 3 and 6 months postinjection, there were neither adverse local effects nor systemic effects observed. CONCLUSIONS The unique design features of the MID-C system, based on polyaxial joints and ceramic coating, resulted in favorable static, fatigue, and wear resistance properties. Wear properties were superior to those published for artificial spinal discs. Long-term outcomes from clinical use will be required to correlate these bench tests to the in vivo reality of clinical use. LEVEL OF EVIDENCE Level V.
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Affiliation(s)
- U Arnin
- Israel Spine Center, Assuta Hospital, Tel Aviv, Israel
| | | | - R R Betz
- Institute for Spine and Scoliosis Lawrenceville, USA
| | | | - Y Floman
- Israel Spine Center, Assuta Hospital, Tel Aviv, Israel
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Biswas JK, Sahu TP, Rana M, Roy S, Karmakar SK, Majumder S, Roychowdhury A. Design factors of lumbar pedicle screws under bending load: A finite element analysis. Biocybern Biomed Eng 2019. [DOI: 10.1016/j.bbe.2018.10.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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25
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Arbash MA, Parambathkandi AM, Baco AM, Alhammoud A. Impact of Screw Type on Kyphotic Deformity Correction after Spine Fracture Fixation: Cannulated versus Solid Pedicle Screw. Asian Spine J 2018; 12:1053-1059. [PMID: 30322251 PMCID: PMC6284117 DOI: 10.31616/asj.2018.12.6.1053] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2017] [Accepted: 05/22/2018] [Indexed: 11/24/2022] Open
Abstract
Study Design Retrospective review. Purpose To detect the effect of cannulated (poly-axial head) and solid (mono-axial head) screws on the local kyphotic angle, vertebral body height, and superior and inferior angles between the screw and the rod in the surgical management of thoracolumbar fractures. Overview of Literature Biomechanics studies showed that the ultimate load, yield strength, and cycles to failure were significantly lower with cannulated (poly-axial head) pedicle comparing to solid core (mono-axial head). Methods The medical charts of patients with thoracolumbar fractures who underwent pedicle screw fixation with cannulated or solid pedicle screws were retrospectively reviewed; the subjects were followed up from January 2011 to December 2015. Results Total 178 patients (average age, 36.1±12.4 years; men, 142 [84.3%]; women, 28 [15.7%]) with thoracolumbar fractures who underwent surgery and were followed up at Hamad Medical Corporation were classified, based on the screw type as those with cannulated screws and those with solid screws. The most commonly affected level was L1, followed by L2 and D12. Surgical correction of the local kyphotic angle was significantly different in the groups; however, there was no significant difference in the loss of correction of the local kyphotic angle of the groups. Surgical correction of the reduction in the vertebral body height showed statistical significance, while the average loss of correction in the reduction of the vertebral body height was not significantly different. The measurement of the angles made by the screws on the rods was not significantly different between the cannulated (poly-axial head) and solid (mono-axial head) screw groups. Conclusions Solid screws were superior in terms of providing increased correction of the kyphotic angle and height of the fractured vertebra than the cannulated screws; however, no difference was noted between the screws in the maintenance of the superior and inferior angles of the screw with the rod.
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Affiliation(s)
| | | | - Abdul Moeen Baco
- Department of Orthopedics, Hamad Medical Corporation, Doha, Qatar
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26
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Wang H, Zhao Y, Mo Z, Han J, Chen Y, Yu H, Wang Q, Liu J, Li C, Zhou Y, Xiang L. Comparison of short-segment monoaxial and polyaxial pedicle screw fixation combined with intermediate screws in traumatic thoracolumbar fractures: a finite element study and clinical radiographic review. Clinics (Sao Paulo) 2017; 72:609-617. [PMID: 29160423 PMCID: PMC5666442 DOI: 10.6061/clinics/2017(10)04] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 07/21/2017] [Indexed: 12/01/2022] Open
Abstract
OBJECTIVES No studies have compared monoaxial and polyaxial pedicle screws with regard to the von Mises stress of the instrumentation, intradiscal pressures of the adjacent segment and adjacent segment degeneration. METHODS Short-segment monoaxial/polyaxial pedicle screw fixation techniques were compared using finite element methods, and the redistributed T11-L1 segment range of motion, largest maximal von Mises stress of the instrumentation, and intradiscal pressures of the adjacent segment under displacement loading were evaluated. Radiographic results of 230 patients with traumatic thoracolumbar fractures treated with these fixations were reviewed, and the sagittal Cobb's angle, vertebral body angle, anterior vertebral body height of the fractured vertebrae and adjacent segment degeneration were calculated and evaluated. RESULTS The largest maximal values of the von Mises stress were 376.8 MPa for the pedicle screws in the short-segment monoaxial pedicle screw fixation model and 439.9 MPa for the rods in the intermediate monoaxial pedicle screw fixation model. The maximal intradiscal pressures of the upper adjacent segments were all greater than those of the lower adjacent segments. The maximal intradiscal pressures of the monoaxial pedicle screw fixation model were larger than those in the corresponding segments of the normal model. The radiographic results at the final follow-up evaluation showed that the mean loss of correction of the sagittal Cobb's angle, vertebral body angle and anterior vertebral body height were smallest in the intermediate monoaxial pedicle screw fixation group. Adjacent segment degeneration was less likely to be observed in the intermediate polyaxial pedicle screw fixation group but more likely to be observed in the intermediate monoaxial pedicle screw fixation group. CONCLUSION Smaller von Mises stress in the pedicle screws and lower intradiscal pressure in the adjacent segment were observed in the polyaxial screw model than in the monoaxial pedicle screw fixation spine models. Fracture-level fixation could significantly correct kyphosis and reduce correction loss, and adjacent segment degeneration was less likely to be observed in the intermediate polyaxial pedicle screw fixation group.
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Affiliation(s)
- Hongwei Wang
- Department of Orthopedics, General Hospital of Shenyang Military Area Command of Chinese PLA, Shenyang, Liaoning, 110016, China
- State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Science, Shenyang, Liaoning, 110016, China
- *Corresponding author. E-mail:
| | - Yiwen Zhao
- State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Science, Shenyang, Liaoning, 110016, China
- #These authors contributed equally to this work
| | - Zhongjun Mo
- National Research Center for Rehabilitation Aids, Beijing, 100176, China
| | - Jianda Han
- State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Science, Shenyang, Liaoning, 110016, China
| | - Yu Chen
- Department of Orthopedics, General Hospital of Shenyang Military Area Command of Chinese PLA, Shenyang, Liaoning, 110016, China
| | - Hailong Yu
- Department of Orthopedics, General Hospital of Shenyang Military Area Command of Chinese PLA, Shenyang, Liaoning, 110016, China
| | - Qi Wang
- Department of Orthopedics, General Hospital of Shenyang Military Area Command of Chinese PLA, Shenyang, Liaoning, 110016, China
| | - Jun Liu
- Department of Orthopedics, General Hospital of Shenyang Military Area Command of Chinese PLA, Shenyang, Liaoning, 110016, China
| | - Changqing Li
- Department of Orthopedics, Xinqiao Hospital, the Third Military Medical University, Chongqing, 400037, China
| | - Yue Zhou
- State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Science, Shenyang, Liaoning, 110016, China
| | - Liangbi Xiang
- Department of Orthopedics, General Hospital of Shenyang Military Area Command of Chinese PLA, Shenyang, Liaoning, 110016, China
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Novel Screw Head Design of Pedicle Screw for Reducing the Correction Loss in the Patients With Thoracolumbar Vertebral Fractures: A Biomechanical Study. Spine (Phila Pa 1976) 2017; 42:E379-E384. [PMID: 27454538 DOI: 10.1097/brs.0000000000001808] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN A biomechanical study. OBJECTIVE To study the different biomechanical property among fixed-axis, monoplanar and polyaxial screws in the static and dynamic tests. SUMMARY OF BACKGROUND DATA Correction loss is a common phenomenon in the patients with thoracolumbar vertebral fractures who underwent the posterior pedicle screw fixation. The incidence varies with the kinds of fixation instrumentation used. There is higher incidence in polyaxial pedicle screws group than in fixed-axis pedicle screws. Monoplanar pedicle screws, which are mobile in the axial plane but fixed in the sagittal plane, can be a better fixation instrumentation for thoracolumbar vertebral fractures in theory. METHODS A total of 30 porcine spinal units (L2-L4) were used for the static and dynamic tests, which were randomized into six groups (A1, A2, A3, B1, B2, and B3). Static test was performed in A1, A2, and A3. In this test, fixed-axis, monoplanar, and polyaxial screws were performed in A1, A2, and A3, respectively. The ultimate load was noted after tested. In addition, dynamic test was performed in B1, B2, and B3, used fixed-axis, monoplanar, and polyaxial screws, respectively. Correction loss (head-shank angle shift and anterior vertebral body height shift) was obtained and analyzed in each mode. RESULTS In static test, fixed-axis and monoplanar screws had significantly higher ultimate load than polyaxial screws (P < 0.05) and fixed-axis screws had a little higher ultimate load than monoplanar screws (P < 0.05). In dynamic test, correction loss was minimal in fixed-axis screws, medium in monoplanar screws, and maximal in polyaxial screws. However, the differences were statistically significant in all comparisons but not in the comparison of fixed-axis and monoplanar screws (P > 0.05). CONCLUSION The findings from the current study suggest that monoplanar screws can significantly increase the stiffness in axial direction compared with polyaxial screws, and reduce the risks of correction loss. For thoracolumbar vertebral fractures, monoplanar screw is a better optional instrumentation for minimally invasive surgery. LEVEL OF EVIDENCE N/A.
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28
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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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Acar N, Karakasli A, Karaarslan AA, Ozcanhan MH, Ertem F, Erduran M. The Mechanical Effect of Rod Contouring on Rod-Screw System Strength in Spine Fixation. J Korean Neurosurg Soc 2016; 59:425-9. [PMID: 27651858 PMCID: PMC5028600 DOI: 10.3340/jkns.2016.59.5.425] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Revised: 05/06/2016] [Accepted: 06/08/2016] [Indexed: 11/27/2022] Open
Abstract
OBJECTIVE Rod-screw fixation systems are widely used for spinal instrumentation. Although many biomechanical studies on rod-screw systems have been carried out, but the effects of rod contouring on the construct strength is still not very well defined in the literature. This work examines the mechanical impact of straight, 20° kyphotic, and 20° lordotic rod contouring on rod-screw fixation systems, by forming a corpectomy model. METHODS The corpectomy groups were prepared using ultra-high molecular weight polyethylene samples. Non-destructive loads were applied during flexion/extension and torsion testing. Spine-loading conditions were simulated by load subjections of 100 N with a velocity of 5 mm min(-1), to ensure 8.4-Nm moment. For torsional loading, the corpectomy models were subjected to rotational displacement of 0.5° s(-1) to an end point of 5.0°, in a torsion testing machine. RESULTS Under both flexion and extension loading conditions the stiffness values for the lordotic rod-screw system were the highest. Under torsional loading conditions, the lordotic rod-screw system exhibited the highest torsional rigidity. CONCLUSION We concluded that the lordotic rod-screw system was the most rigid among the systems tested and the risk of rod and screw failure is much higher in the kyphotic rod-screw systems. Further biomechanical studies should be attempted to compare between different rod kyphotic angles to minimize the kyphotic rod failure rate and to offer a more stable and rigid rod-screw construct models for surgical application in the kyphotic vertebrae.
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Affiliation(s)
- Nihat Acar
- Department of Orthopaedics and Traumatology, Ilyas Cokay Catalca Hospital, Catalca, Istanbul, Turkey
| | - Ahmet Karakasli
- Department of Orthopaedics and Traumatology, Faculty of Medicine, Dokuz Eylul University, Balcova, Izmir, Turkey
| | - Ahmet A Karaarslan
- Department of Orthopedics and Traumatology, Sifa Hospital, Konak, Izmir, Turkey
| | - Mehmet Hilal Ozcanhan
- Department of Computer Engineering, Faculty of Engineering, Dokuz Eylul University, Tinaztepe, Izmir, Turkey
| | - Fatih Ertem
- Department of Biomechanics, Health Science Institute, Dokuz Eylul University, Balcova, Izmir, Turkey
| | - Mehmet Erduran
- Department of Orthopaedics and Traumatology, Faculty of Medicine, Dokuz Eylul University, Balcova, Izmir, Turkey
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Kubosch D, Kubosch EJ, Gueorguiev B, Zderic I, Windolf M, Izadpanah K, Südkamp NP, Strohm PC. Biomechanical investigation of a minimally invasive posterior spine stabilization system in comparison to the Universal Spinal System (USS). BMC Musculoskelet Disord 2016; 17:134. [PMID: 27005301 PMCID: PMC4804481 DOI: 10.1186/s12891-016-0983-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 03/10/2016] [Indexed: 04/08/2023] Open
Abstract
Background Although minimally invasive posterior spine implant systems have been introduced, clinical studies reported on reduced quality of spinal column realignment due to correction loss. The aim of this study was to compare biomechanically two minimally invasive spine stabilization systems versus the Universal Spine Stabilization system (USS). Methods Three groups with 5 specimens each and 2 foam bars per specimen were instrumented with USS (Group 1) or a minimally invasive posterior spine stabilization system with either polyaxial (Group 2) or monoaxial (Group 3) screws. Mechanical testing was performed under quasi-static ramp loading in axial compression and torsion, followed by destructive cyclic loading run under axial compression at constant amplitude and then with progressively increasing amplitude until construct failure. Bending construct stiffness, torsional stiffness and cycles to failure were investigated. Results Initial bending stiffness was highest in Group 3, followed by Group 2 and Group 1, without any significant differences between the groups. A significant increase in bending stiffness after 20’000 cycles was observed in Group 1 (p = 0.002) and Group 2 (p = 0.001), but not in Group 3, though the secondary bending stiffness showed no significant differences between the groups. Initial and secondary torsional stiffness was highest in Group 1, followed by Group 3 and Group 2, with significant differences between all groups (p ≤ 0.047). A significant increase in initial torsional stiffness after 20’000 cycles was observed in Group 2 (p = 0.017) and 3 (p = 0.013), but not in Group 1. The highest number of cycles to failure was detected in Group 1, followed by Group 3 and Group 2. This parameter was significantly different between Group 1 and Group 2 (p = 0.001), between Group 2 and Group 3 (p = 0.002), but not between Group 1 and Group 3. Conclusions These findings quantify the correction loss for minimally invasive spine implant systems and imply that unstable spine fractures might benefit from stabilization with conventional implants like the USS.
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Affiliation(s)
- D Kubosch
- Department of Orthopaedic and Trauma Surgery, University of Freiburg Medical Center, Hugstetterstr. 55, D-79106, Freiburg im Breisgau, Germany.
| | - E J Kubosch
- Department of Orthopaedic and Trauma Surgery, University of Freiburg Medical Center, Hugstetterstr. 55, D-79106, Freiburg im Breisgau, Germany
| | - B Gueorguiev
- AO Research Institute Davos, Clavadelerstrasse 8, CH-7270, Davos, Switzerland
| | - I Zderic
- AO Research Institute Davos, Clavadelerstrasse 8, CH-7270, Davos, Switzerland
| | - M Windolf
- AO Research Institute Davos, Clavadelerstrasse 8, CH-7270, Davos, Switzerland
| | - K Izadpanah
- Department of Orthopaedic and Trauma Surgery, University of Freiburg Medical Center, Hugstetterstr. 55, D-79106, Freiburg im Breisgau, Germany
| | - N P Südkamp
- Department of Orthopaedic and Trauma Surgery, University of Freiburg Medical Center, Hugstetterstr. 55, D-79106, Freiburg im Breisgau, Germany
| | - P C Strohm
- Department of Orthopaedic and Trauma Surgery, University of Freiburg Medical Center, Hugstetterstr. 55, D-79106, Freiburg im Breisgau, Germany
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Li J, Shang J, Zhou Y, Li C, Liu H. Finite Element Analysis of a New Pedicle Screw-Plate System for Minimally Invasive Transforaminal Lumbar Interbody Fusion. PLoS One 2015; 10:e0144637. [PMID: 26649749 PMCID: PMC4674154 DOI: 10.1371/journal.pone.0144637] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Accepted: 11/20/2015] [Indexed: 11/25/2022] Open
Abstract
PURPOSE Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is increasingly popular for the surgical treatment of degenerative lumbar disc diseases. The constructs intended for segmental stability are varied in MI-TLIF. We adopted finite element (FE) analysis to compare the stability after different construct fixations using interbody cage with posterior pedicle screw-rod or pedicle screw-plate instrumentation system. METHODS A L3-S1 FE model was modified to simulate decompression and fusion at L4-L5 segment. Fixation modes included unilateral plate (UP), unilateral rod (UR), bilateral plate (BP), bilateral rod (BR) and UP+UR fixation. The inferior surface of the S1 vertebra remained immobilized throughout the load simulation, and a bending moment of 7.5 Nm with 400N pre-load was applied on the L3 vertebra to recreate flexion, extension, lateral bending, and axial rotation. Range of motion (ROM) and Von Mises stress were evaluated for intact and instrumentation models in all loading planes. RESULTS All reconstructive conditions displayed decreased motion at L4-L5. The pedicle screw-plate system offered equal ROM to pedicle screw-rod system in unilateral or bilateral fixation modes respectively. Pedicle screw stresses for plate system were 2.2 times greater than those for rod system in left lateral bending under unilateral fixation. Stresses for plate were 3.1 times greater than those for rod in right axial rotation under bilateral fixation. Stresses on intervertebral graft for plate system were similar to rod system in unilateral and bilateral fixation modes respectively. Increased ROM and posterior instrumentation stresses were observed in all loading modes with unilateral fixation compared with bilateral fixation in both systems. CONCLUSIONS Transforaminal lumbar interbody fusion augmentation with pedicle screw-plate system fixation increases fusion construct stability equally to the pedicle screw-rod system. Increased posterior instrumentation stresses are observed in all loading modes with plate fixation, and bilateral fixation could reduce stress concentration.
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Affiliation(s)
- Jie Li
- Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, China
| | - Jin Shang
- Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, China
| | - Yue Zhou
- Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, China
| | - Changqing Li
- Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, China
| | - Huan Liu
- Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, China
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Shih KS, Hsu CC, Hou SM, Yu SC, Liaw CK. Comparison of the bending performance of solid and cannulated spinal pedicle screws using finite element analyses and biomechanical tests. Med Eng Phys 2015. [DOI: 10.1016/j.medengphy.2015.06.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Liu ZD, Li XF, Qian L, Wu LM, Lao LF, Wang HT. Lever reduction using polyaxial screw and rod fixation system for the treatment of degenerative lumbar spondylolisthesis with spinal stenosis: technique and clinical outcome. J Orthop Surg Res 2015; 10:29. [PMID: 25890019 PMCID: PMC4355151 DOI: 10.1186/s13018-015-0168-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2014] [Accepted: 01/19/2015] [Indexed: 11/10/2022] Open
Abstract
Background The management for degenerative lumbar spondylolisthesis with spinal stenosis remains controversial. Reduction of lumbar spondylolisthesis has been performed via numerous techniques. Most of them need extra reduction assembly. Methods In this retrospective analysis, 27 patients of degenerative lumbar spondylolisthesis with spinal stenosis underwent reduction using polyaxial screw and rod constructs and posterolateral fusion. The average age at the time of surgery was 53 ± 3.23 years. The outcome measures consisted of a radiographic assessment of deformity and fusion rate and a clinical assessment of perioperative improvement in low back pain and function. Preoperative and postoperative radiographic evaluation included the percent slip, slip angle, and the lumbar lordosis between L1 and the sacrum measured using the Cobb method. Before surgery and at the final follow-up, the Oswestry Disability Index (ODI) and the visual pain analog scale (VPAS) between 0 (no pain) and 10 (maximal pain) were quantified. Results The average follow-up period more than 5 years was available. The mean operative time was 90.19 ± 14.51 min, and the mean blood loss during surgery was 152.59 ± 45.71 ml. The mean length of incision was 4.83 ± 0.63 cm. The average percent slippage and the mean slip angle were, respectively, 19.8 ± 4.49% and 9.69 ± 3.79° before surgery, 5.09 ± 3.40% and 6.39 ± 3.16° after surgery, and 5.67 ± 3.92% and 7.21 ± 3.05° at the last follow-up. The average lumbar lordosis was 36.88 ± 2.64° before surgery, 41.96 ± 1.64° after surgery, and 40.27 ± 1.19° at the final follow-up. No neurologic deficit occurred. Solid fusion was achieved for all cases. Compared with the outcome preoperation, the data improved from 6.56 ± 1.40 to 2.48 ± 1.16 for VPAS pain scores and from 32.22 ± 3.57 to 10.93 ± 4.93 for the ODI at the final follow-up. Conclusions Lever slip reduction maneuver techniques using polyaxial screw and rod fixation system was simple and practicable. The treatment outcomes showed satisfactory radiographic characteristics and clinical results. The length of the incision was relatively small with a low intraoperative blood loss and short operation time.
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Affiliation(s)
- Zu-De Liu
- Department of Orthopaedic Surgery, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
| | - Xin-Feng Li
- Department of Orthopaedic Surgery, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
| | - Lie Qian
- Department of Orthopaedic Surgery, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
| | - Lian-Ming Wu
- Department of Radiology, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
| | - Li-Feng Lao
- Department of Orthopaedic Surgery, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
| | - Han-Tao Wang
- Department of Orthopaedic Surgery, Ren Ji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
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Abstract
Background Laboratory spinal biomechanical tests using human cadaveric or animal spines have limitations in terms of disease transmission, high sample variability, decay and fatigue during extended testing protocols. Therefore, a synthetic biomimetic spine model may be an acceptable substitute. The goal of current study is to evaluate the properties of a synthetic biomimetic spine model; also to assess the mechanical performance of lateral plating following lateral interbody fusion. Methods Three L3/4 synthetic spinal motion segments were examined using a validated pure moment testing system. Moments (±7.5 Nm) were applied in flexion-extension (FE), lateral bending (LB) and axial rotation (AR) at 1Hz for total 10000 cycles in MTS Bionix. An additional test was performed 12 hours after 10000 cycles. A ±10 Nm cycle was also performed to allow provide comparison to the literature. For implantation evaluation, each model was tested in the 4 following conditions: 1) intact, 2) lateral cage alone, 3) lateral cage and plate 4) anterior cage and plate. Results were analysed using ANOVA with post-hoc Tukey’s HSD test. Results Range of motion (ROM) exhibited logarithmic growth with cycle number (increases of 16%, 37.5% and 24.3% in AR, FE and LB respectively). No signification difference (p > 0.1) was detected between 4 cycles, 10000 cycles and 12 hour rest stages. All measured parameters were comparable to that of reported cadaveric values. The ROM for a lateral cage and plate construct was not significantly different to the anterior lumbar interbody construct for FE (p = 1.00), LB (p = 0.995) and AR (p = 0.837). Conclusions Based on anatomical and biomechanical similarities, the synthetic spine tested here provides a reasonable model to represent the human lumbar spine. Repeated testing did not dramatically alter biomechanics which may allow non-destructive testing between many different procedures and devices without the worry of carry over effects. Small intra-specimen variability and lack of biohazard makes this an attractive alternative for in vitro spine biomechanical testing. It also proved an acceptable surrogate for biomechanical testing, confirming that a lateral lumbar interbody cage and plate construct reduces ROM to a similar degree as anterior lumbar interbody cage and plate constructs.
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La Barbera L, Galbusera F, Villa T, Costa F, Wilke HJ. ASTM F1717 standard for the preclinical evaluation of posterior spinal fixators: Can we improve it? Proc Inst Mech Eng H 2014; 228:1014-26. [DOI: 10.1177/0954411914554244] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Preclinical evaluation of spinal implants is a necessary step to ensure their reliability and safety before implantation. The American Society for Testing and Materials reapproved F1717 standard for the assessment of mechanical properties of posterior spinal fixators, which simulates a vertebrectomy model and recommends mimicking vertebral bodies using polyethylene blocks. This set-up should represent the clinical use, but available data in the literature are few. Anatomical parameters depending on the spinal level were compared to published data or measurements on biplanar stereoradiography on 13 patients. Other mechanical variables, describing implant design were considered, and all parameters were investigated using a numerical parametric finite element model. Stress values were calculated by considering either the combination of the average values for each parameter or their worst-case combination depending on the spinal level. The standard set-up represents quite well the anatomy of an instrumented average thoracolumbar segment. The stress on the pedicular screw is significantly influenced by the lever arm of the applied load, the unsupported screw length, the position of the centre of rotation of the functional spine unit and the pedicular inclination with respect to the sagittal plane. The worst-case combination of parameters demonstrates that devices implanted below T5 could potentially undergo higher stresses than those described in the standard suggestions (maximum increase of 22.2% at L1). We propose to revise F1717 in order to describe the anatomical worst case condition we found at L1 level: this will guarantee higher safety of the implant for a wider population of patients.
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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
| | - Francesco Costa
- Department of Neurosurgery, Humanitas Clinical and Research Center, Milano, Italy
| | - Hans-Joachim Wilke
- Institute of Orthopaedic Research and Biomechanics, Centre of Musculoskeletal Research Ulm (ZMFU), Ulm University, Ulm, Germany
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Schroerlucke SR, Steklov N, Mundis GM, Marino JF, Akbarnia BA, Eastlack RK. How does a novel monoplanar pedicle screw perform biomechanically relative to monoaxial and polyaxial designs? Clin Orthop Relat Res 2014; 472:2826-32. [PMID: 24920048 PMCID: PMC4117910 DOI: 10.1007/s11999-014-3711-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Accepted: 05/20/2014] [Indexed: 01/31/2023]
Abstract
BACKGROUND Minimally invasive spinal fusions frequently require placement of pedicle screws through small incisions with limited visualization. Polyaxial pedicle screws are favored due to the difficulty of rod insertion with fixed monoaxial screws. Recently, a novel monoplanar screw became available that is mobile in the coronal plane to ease rod insertion but fixed in the sagittal plane to eliminate head slippage during flexion loads; however, the strength of this screw has not been established relative to other available screw designs. QUESTIONS/PURPOSES We compared the static and dynamic load to failure in polyaxial, monoaxial, and monoplanar pedicle screws. METHODS Six different manufacturers' screws (42 total) were tested in three categories (polyaxial, n = 4; monoaxial, n = 1; monopolar, n = 1) utilizing titanium rods. An additional test was performed using cobalt-chromium rods with the monopolar screws only. Screws were embedded into polyethylene blocks and rods were attached using the manufacturers' specifications. Static and dynamic testing was performed. Dynamic testing began at 80% of static yield strength at 1 Hz for 50,000 cycles. RESULTS In static testing, monoaxial and monoplanar screws sustained higher loads than all polyaxial screw designs (range, 37%-425% higher; p < 0.001). The polyaxial screws failed at the head-screw interface, while the monoaxial and monoplanar screws failed by rod breakage in the static test. The dynamic loads to failure were greater with the monoplanar and monoaxial screws than with the polyaxial screws (range, 35%-560% higher; p < 0.001). With dynamic testing, polyaxial screws failed via screw-head slippage between 40% and 95% of static yield strength, while failures in monoaxial and monoplanar screws resulted from either screw shaft or rod breakage. CONCLUSIONS All polyaxial screws failed at the screw-head interface in static and dynamic testing and at lower values than monoaxial/monoplanar screw designs. Monoplanar and monoaxial screws failed at forces well above expected in vivo values; this was not the case for most polyaxial screws. CLINICAL RELEVANCE Polyaxial screw heads slip on the screw shank at lower values than monoaxial or monoplanar screws, and this results in angular change between the rod and pedicle screw, which could cause loss of segmental lordosis. The novel monoplanar screw used in this study may combine ease of rod placement with sagittal plane strength.
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Affiliation(s)
| | - Nikolai Steklov
- />Shiley Center for Orthopaedic Research and Education at Scripps Clinic, La Jolla, CA USA
| | | | | | | | - Robert K. Eastlack
- />Division of Orthopaedic Surgery, Shiley Center for Orthopaedic Research and Education at Scripps Clinic, 10666 North Torrey Pines Road, MS116, La Jolla, CA 92037 USA
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Villa T, La Barbera L, Galbusera F. Comparative analysis of international standards for the fatigue testing of posterior spinal fixation systems. Spine J 2014; 14:695-704. [PMID: 24268390 DOI: 10.1016/j.spinee.2013.08.032] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2013] [Revised: 07/19/2013] [Accepted: 08/23/2013] [Indexed: 02/03/2023]
Abstract
BACKGROUND CONTEXT Preclinical evaluation of the long-term reliability of devices for lumbar fixation is a mandatory activity before they are put into market. The experimental setups are described in two different standards edited by the International Organization for Standardization (ISO) and the American Society for Testing Materials (ASTM), but the evaluation of the suitability of such tests to simulate the actual loading with in vivo situations has never been performed. PURPOSE To calculate through finite element (FE) simulations the stress in the rods of the fixator when subjected to ASTM and ISO standards. To compare the calculated stresses arising in the same fixator once it has been virtually mounted in a physiological environment and loaded with physiological forces and moments. STUDY DESIGN FE simulations and validation experimental tests. METHODS FE models of the ISO and ASTM setups were created to conduct simulations of the tests prescribed by standards and calculate stresses in the rods. Validation of the simulations were performed through experimental tests; the same fixator was virtually mounted in an L2-L4 FE model of the lumbar spine and stresses in the rods were calculated when the spine was subjected to physiological forces and moments. RESULTS The comparison between FE simulations and experimental tests showed good agreement between results obtained using the two methodologies, thus confirming the suitability of the FE method to evaluate stresses in the device in different loading situations. The usage of a physiological load with ASTM standard is impossible due to the extreme severity of the ASTM configuration; in this circumstance, the presence of an anterior support is suggested. Also, ISO prescriptions, although the choice of the setup correctly simulates the mechanical contribution of the discs, seem to overstress the device as compared with a physiological loading condition. Some daily activities, other than walking, can induce a further state of stress in the device that should be taken into account in setting up new experimental procedures. CONCLUSIONS ISO standard loading prescriptions seems to be more severe than the expected physiological ones. The ASTM standard should be completed by including some anterior supporting device and declaring the value of the load to be imposed. Moreover, a further enhancement of standards would be simulating other movements representative of daily activities different from walking.
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Affiliation(s)
- Tomaso Villa
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, 20133, Milano, Italy; IRCCS Istituto Ortopedico Galeazzi, Via Galeazzi 4, 20161, Milano, Italy.
| | - Luigi La Barbera
- Laboratory of Biological Structure Mechanics, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, 20133, Milano, Italy; IRCCS Istituto Ortopedico Galeazzi, Via Galeazzi 4, 20161, Milano, Italy
| | - Fabio Galbusera
- IRCCS Istituto Ortopedico Galeazzi, Via Galeazzi 4, 20161, Milano, Italy; Institute of Orthopaedic Research and Biomechanics, Center of Musculoskeletal Research Ulm, University of Ulm, Helmholtzstr. 14, 89081, Ulm, Germany
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Kim TH, Lee BH, Moon SH, Lee SH, Lee HM. Comparison of adjacent segment degeneration after successful posterolateral fusion with unilateral or bilateral pedicle screw instrumentation: a minimum 10-year follow-up. Spine J 2013; 13:1208-16. [PMID: 24075027 DOI: 10.1016/j.spinee.2013.07.431] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Revised: 02/20/2013] [Accepted: 07/03/2013] [Indexed: 02/03/2023]
Abstract
BACKGROUND CONTEXT In the instrumented fusion, adjacent segment facet joint violation or impingement by pedicle screws is unavoidable especially in cephalad segment, despite taking specific intraoperative precautions in terms of surgical approach. In such circumstances, unlike its original purpose, unilateral pedicle screw instrumentation can contribute to reduce the degeneration of cephalad adjacent segment by preventing contralateral cephalad adjacent facet joint from the unavoidable injury by pedicle screw insertion. However, to our knowledge, no long-term follow-up study has compared adjacent segment degeneration (ASD) between unilateral and bilateral pedicle screw instrumented fusion. PURPOSE To compare ASD after successful posterolateral fusion using either unilateral or bilateral pedicle screw instrumentation for patients with lumbar spinal stenosis and/or Grade 1 spondylolisthesis. STUDY DESIGN Retrospective case-control study. PATIENT SAMPLE One hundred forty-seven patients who had undergone one- or two-level posterolateral fusion with unilateral or bilateral pedicle screw instrumentation for lumbar spinal stenosis with or without low-grade spondylolisthesis and achieved successful fusion, with a minimum 10-year follow-up. OUTCOME MEASURE The occurrence of radiologic ASD, Oswestry disability index (ODI) scores, and revision rates. METHODS A total of 194 consecutive patients were contacted and encouraged to visit our hospital and to participate in our study. Radiologic ASD was evaluated at three motion segments: cephalad adjacent segment (first cephalad adjacent segment), one cephalad to cephalad adjacent segment (second cephalad adjacent segment), and caudal adjacent segment. Clinical outcomes were compared by ODI scores and revision rates. RESULTS In total, 147 of 194 (75.8%) patients were available for at least 10 years of radiologic and clinical follow-up. Adjacent segment degeneration (in first cephalad or caudal adjacent segment) was noted in 55.9% (33 of 59 patients) of the unilateral group and 72.7% (64 of 88 patients) of the bilateral group (p=.035). The occurrence of ASD in each first cephalad and caudal adjacent segment was not significantly different between groups but that in second cephalad adjacent segment was significantly different between groups (p=.004). Clinical outcomes according to ODI showed significant difference between groups (p=.016), especially when ODI scores were compared in patients with ASD (p=.004). CONCLUSIONS In a minimum 10-year follow-up retrospective study of posterolateral fusion for lumbar spinal stenosis and/or Grade 1 spondylolisthesis, unilateral pedicle screw instrumentation showed a lower rate of radiologic ASD, especially in second cephalad adjacent segment, and a better clinical outcome by ODI.
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Affiliation(s)
- Tae-Hwan Kim
- Department of Orthopedic Surgery, Yonsei University College of Medicine, CPO Box 8044, 50 Yonsei-Ro, Seodaemun-gu, Seoul 120-752, Korea
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Wang H, Li C, Liu T, Zhao WD, Zhou Y. Biomechanical efficacy of monoaxial or polyaxial pedicle screw and additional screw insertion at the level of fracture, in lumbar burst fracture: An experimental study. Indian J Orthop 2012; 46:395-401. [PMID: 22912513 PMCID: PMC3421928 DOI: 10.4103/0019-5413.98827] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Use of a pedicle screw at the level of fracture, also known as an intermediate screw, has been shown to improve clinical results in managing lumbar fracture, but there is a paucity of biomechanical studies to support the claim. The aim of this study was to evaluate the effect of adding intermediate pedicle screws at the level of a fracture on the stiffness of a short-segment pedicle fixation using monoaxial or polyaxial screws and to compare the strength of monoaxial and polyaxial screws in the calf spine fracture model. MATERIALS AND METHODS Flexibility of 12 fresh-frozen calf lumbar spine specimens was evaluated in all planes. An unstable burst fracture model was created at the level of L3 by the pre-injury and dropped-mass technique. The specimens were randomly divided into monoaxial pedicle screw (MPS) and polyaxial pedicle screw (PPS) groups. Flexibility was retested without and with intermediate screws (MPSi and PPSi) placed at the level of fracture in addition to standard screws placed at L2 and L4. RESULTS The addition of intermediate screws significantly increased the stability of the constructs, as measured by a decreased range of motion (ROM) in flexion, extension, and lateral bending in both MPS and PPS groups (P < 0.05). There was neither any significant difference in the ROM in the spines of the two groups before injury, nor a difference in the ROM between the MPSi and PPSi groups (P > 0.05), but there was a significant difference between MPS and PPS in flexion and extension in the short-segment fixation group (P < 0.05). CONCLUSIONS The addition of intermediate screws at the level of a burst fracture significantly increased the stability of short-segment pedicle screw fixation in both the MPS and PPS groups. However, in short-segment fixation group, monoaxial pedicle screw exhibited more stability in flexion and extension than the polyaxial pedicle screw.
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Affiliation(s)
- Hongwei Wang
- Department of Orthopedics, Xinqiao Hospital, Third Military Medical University, Xinqiao Street, Chongqing, China
| | - Changqing Li
- Department of Orthopedics, Xinqiao Hospital, Third Military Medical University, Xinqiao Street, Chongqing, China
| | - Tao Liu
- Department of Orthopedics, Xinqiao Hospital, Third Military Medical University, Xinqiao Street, Chongqing, China
| | - Wei-dong Zhao
- Department of Anatomy, Biomechanical Laboratory, Southern Medical University, Guangzhou 510515, China
| | - Yue Zhou
- Department of Orthopedics, Xinqiao Hospital, Third Military Medical University, Xinqiao Street, Chongqing, China,Address for correspondence: Dr. Yue Zhou, Department of Orthopedics, Xinqiao Hospital, Third Military Medical University, 83 Xinqiao Street, Chongqing 400037, PR China. E-mail:
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Demir T, Camuşcu N. Design and performance of spinal fixation pedicle screw system. Proc Inst Mech Eng H 2011; 226:33-40. [DOI: 10.1177/0954411911427351] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Pedicle screw-rod bilateral constructions are extensively used in spinal fixation. In this study, the common cause for failure of bilateral constructions has been determined to be the high stress concentration at the rod–setscrew interface. In order to overcome this problem, a design modification has been made by using a supplementary part (shoe) between rod and setscrew. Performance comparison of the conventional design and modified design has been done by conducting static tests. Design modification has resulted in 11%, 27%, 42% and 31% improvements in axial gripping capacity, torsional gripping capacity, flexion/extension resistance and subassembly compression strength, respectively. The most outstanding achievement has been obtained in the fatigue life, which was extended by almost three times.
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Affiliation(s)
- Teyfik Demir
- Department of Biomedical Engineering, TOBB University of Economics and Technology, Turkey
| | - Necip Camuşcu
- Department of Mechanical Engineering, TOBB University of Economics and Technology, Turkey
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Okamoto T, Neo M, Fujibayashi S, Ito H, Takemoto M, Nakamura T. Mechanical implant failure in posterior cervical spine fusion. 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 2011; 21:328-34. [PMID: 22002474 DOI: 10.1007/s00586-011-2043-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Revised: 08/11/2011] [Accepted: 10/04/2011] [Indexed: 10/16/2022]
Abstract
PURPOSE The aim of this study was to determine whether the recent refinement and downsizing of the implants for posterior cervical fusion increase the occurrence of implant failure. METHODS One hundred forty-two consecutive cases of cervical fusion, using either cannulated Magerl screws or a multiaxial pedicle screw-rod system, were reviewed retrospectively after an average follow-up period of more than 3 years, and the rate and characteristics of the failure of these implants were evaluated. RESULTS Implant failure occurred in six (4.2%) patients: five with rheumatoid arthritis and one with athetoid cerebral palsy. Occipital plate fracture occurred in two patients, Magerl screw breakage in one patient, cervical pedicle screw fracture in two patients, and disassembly of the pedicle screw and rod in two patients (one with an occipital plate fracture). There was no rod fracture. The implant failures were asymptomatic, except in one patient. Disassembly of the pedicle screw and rod was observed immediately after another surgical procedure under general anesthesia in two patients. CONCLUSIONS The failure rate of 4.2% was similar to the rates reported in the literature for posterior lumbar spinal fusion, confirming the reliability of the recent cervical screw-rod system.
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Affiliation(s)
- Takeshi Okamoto
- Department of Orthopaedic Surgery, Kyoto University Graduate School of Medicine, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
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Oliveira MPDC, França LCDM, Ruggani MG, Pedrosa LOG, Fontes BPC, Macedo RDD, Duarte RG, Duarte MGP. Estudo biomecânico comparativo da resistência a forças de compressão entre os parafusos pediculares poliaxiais com travamento tipo Dytech® e parafusos pediculares poliaxiais com travamento tipo Lock 1®. COLUNA/COLUMNA 2010. [DOI: 10.1590/s1808-18512010000300003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
OBJETIVO: Comparar a rigidez de um sistema de fixação pedicular composto por parafusos pediculares poliaxiais de travamento tipo Dytech® com outro composto por parafusos pediculares poliaxiais com travamento do tipo Lock 1®, submetidos a forças de compressão. MÉTODOS: A amostra utilizada para avaliar os sistemas de fixação respeitou as regras do padrão formulado pela American Society for Testing Materials (ASTM) no ensaio F1717-04. Os modelos foram divididos em: Grupo 1, composto pelos ensaios de parafusos poliaxiais com sistema Dytech® de travamento, e o Grupo 2, formado por parafusos poliaxiais com travamento tipo Lock 1®. Foram testados três conjuntos completos montados. Cada sistema foi testado uma única vez por ser esse um ensaio destrutivo. O instrumental implantado foi produzido com titânio de mesma origem. Os grupos experimentais foram submetidos a testes mecânicos na máquina universal de ensaios EMIC, modelo EMIC DL 10000®. RESULTADOS: Os resultados de compressão nas amostras do Grupo 1 tiveram uma carga máxima média de 967,17 N e carga de escoamento média de 804,71 N. Nas amostras do Grupo 2 tivemos uma carga máxima média de 906,04 N e carga de escoamento média de 834,56 N. A respeito da integridade dos instrumentais metálicos usados, não foi observado nenhum tipo de escorregamento ou soltura de porcas, parafusos ou outros componentes. CONCLUSÃO: O sistema de parafusos poliaxiais com travamento tipo Dytech® apresentou valores de rigidez maiores, enquanto o sistema de parafusos com travamento tipo Lock 1® mostrou deslocamento máximo maior.
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Marino JF. Nonfusion short fixation of A3 burst fractures, loss of fixation attributable to polyaxial screw slippage? Spine J 2010; 10:459-60; author reply 460. [PMID: 20421080 DOI: 10.1016/j.spinee.2010.01.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Accepted: 01/27/2010] [Indexed: 02/03/2023]
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Marino JF. Subsidence of metal interbody cage after posterior lumbar interbody fusion with pedicle screw fixation. Orthopedics 2010; 33:226-7; author reply 226-7. [PMID: 20415345 DOI: 10.3928/01477447-20100225-32] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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Ponnappan RK, Serhan H, Zarda B, Patel R, Albert T, Vaccaro AR. Biomechanical evaluation and comparison of polyetheretherketone rod system to traditional titanium rod fixation. Spine J 2009; 9:263-7. [PMID: 18838341 DOI: 10.1016/j.spinee.2008.08.002] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2008] [Accepted: 08/05/2008] [Indexed: 02/03/2023]
Abstract
BACKGROUND CONTEXT Polyetheretherketone (PEEK) has been increasingly used as a biomaterial for spinal implants. PEEK lumbar fusion rods have recently become available for use in posterior lumbar fusion procedures. PURPOSE To compare Polyetheretherketone Rod System to traditional titanium rod fixation in a cadaveric model and provide mechanical test data for the PEEK system. STUDY DESIGN Biomechanical testing. METHODS Cadaveric biomechanical testing was conducted to compare Expedium 5.5 mm PEEK rods to titanium rods of equivalent diameter. Biomaterials testing was performed to determine static and dynamic performance of Expedium 5.5 mm PEEK rods with 6% BaSo4 in compressive bending and torsion. RESULTS Cadaveric testing demonstrated that PEEK rods can significantly reduce the range of motion of a destabilized segment. The testing showed no significant difference in the stability provided by PEEK and titanium rods in posterolateral fusion (PLF) or posterior lumbar interbody fusion (PLIF) constructs. PEEK static compressive bending tests showed 67 degrees displacement without fracture of the rod. Torsion testing showed 30 degrees of rotation without yield or plastic deformation. Dynamic compression testing revealed two fatigue runouts at 23 degrees. CONCLUSIONS PEEK rods provide comparable stability to titanium rods of equivalent diameter in cadaveric testing. Mechanical testing suggests PEEK rods can withstand far beyond the angular displacements suggested by cadaveric testing and that of normal physiologic range of motion. Potential advantages to PEEK rods include better anterior column load sharing, reduced stress at bone-to-screw interface, and reduced computed tomography and magnetic resonance imaging scatter and artifact.
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Affiliation(s)
- Ravi K Ponnappan
- Department of Orthopaedic Surgery, Jefferson Medical College, 925 Chestnut Street, Philadelphia, PA 19107, USA.
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Effect of insertional temperature on the pullout strength of pedicle screws inserted into thoracic vertebrae: an in vitro calf study. Spine (Phila Pa 1976) 2008; 33:E667-72. [PMID: 18758347 DOI: 10.1097/brs.0b013e31817c4f9c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN The axial pullout strength of pedicle screws that were at different temperatures when inserted was compared in calf vertebrae. OBJECTIVE To determine if insertional temperature of the screw itself affects pullout strength. SUMMARY OF BACKGROUND DATA Fixation stability of pedicle screws depend on several factors. The development of alternate insertion techniques and screw designs were used to improve the stability. Polymethylmethacrylate and calcium sulfate augmentation have been shown to be viable options for improving fixation; but have the potential disadvantages. METHODS Three cadaveric thoracic calf spines were instrumented between T1-T10 bilaterally with one type of pedicle screws stored at different insertional temperatures. The axial pullout tests were performed at cross head speed of 5 mm/min. Pullout loads and displacement were recorded at 1/20 seconds intervals until failure occurred. RESULTS The highest pullout force was obtained with the screws inserted at 4 degrees C. These screws had a 19% increase in pullout strength compared with the screws inserted at 24 degrees C. The highest force/torque proportion was gained in the same group as 0.30 kn/Nm. CONCLUSION The technique showed increased pullout force with the screws inserted at 4 degrees C. Using pedicle screws stored at 4 degrees C before instrumentation, seems reasonable in an attempt to obtain a better bone-screw interface.
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Increasing bending strength and pullout strength in conical pedicle screws: biomechanical tests and finite element analyses. ACTA ACUST UNITED AC 2008; 21:130-8. [PMID: 18391719 DOI: 10.1097/bsd.0b013e318073cc4b] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
STUDY DESIGN Comparative in vitro biomechanical study and finite element analysis. OBJECTIVES To investigate the bending strength and pullout strength of conical pedicle screws, as compared with conventional cylindrical screws. SUMMARY OF BACKGROUND DATA Transpedicle screw fixation, the gold standard of spinal fixation, is threatened by screw failure. Conical screws can resist screw breakage and loosening. However, biomechanical studies of bending strength have been lacking, and the results of pullout studies have varied widely. METHODS Ten types of pedicle screws with different patterns of core tapering and core diameter were specially manufactured with good control of all other design factors. The stiffness, yielding strength, and fatigue life of the pedicle screws were assessed by cantilever bending tests using high-molecular-weight polyethylene. The pullout strength was assessed by pullout tests using polyurethane foam. Concurrently, 3-dimensional finite element models simulating these mechanical tests were created, and the results were correlated to those of the mechanical tests. RESULTS In bending tests, conical screws had substantially higher stiffness, yielding strength, and fatigue life than cylindrical screws (P<0.01), especially when there was no step at the thread-shank junction. In pullout tests, pullout strength was higher in screws with a conical core and smaller core diameter and also in situations with higher foam density (P<0.01). In finite element analysis, the maximal deflection and maximal tensile stress were closely related to yielding strength (r=-0.91) and fatigue life (r=-0.95), respectively, in the bending analyses. The total reaction force was closely related to the pullout strength in pullout analyses (r=0.84 and 0.91 for different foam densities). CONCLUSIONS Conical screws effectively increased the bending strength and pullout strength simultaneously. The finite element analyses reliably predicted the results of the mechanical tests.
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The successful short-term treatment of flexion-distraction injuries of the thoracic spine using posterior-only pedicle screw instrumentation. ACTA ACUST UNITED AC 2008; 21:192-8. [PMID: 18458589 DOI: 10.1097/bsd.0b013e318074ddcd] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
STUDY DESIGN In this retrospective study, the results of treating unstable flexion-distraction injuries (FDI) of the thoracic spine with posterior-only thoracic pedicle screw (P/TPS) instrumentation were investigated. OBJECTIVE The objective was to determine the ability of P/TPS to correct and maintain the focal kyphosis of the injured spine. Clinical outcome and complications of the surgical procedure were also a focus of the study. SUMMARY OF BACKGROUND DATA The treatment of FDI of the thoracic spine remains controversial. There continues to be difficulty in maintaining the corrected kyphosis angle regardless of the surgical approach used. METHODS Eighteen patients with FDI of thoracic spine who underwent P/TPS were identified. The initial and corrected focal kyphosis was evaluated radiographically. Failure of treatment was defined as a >5-degree progression of corrected kyphosis from initial to latest follow-up. Clinical evaluation included complication rate, Injury Severity Score, and Frankel grade. RESULTS Of the 18 eligible patients, 15 (83%) had adequate follow-up for evaluation. The mean length of follow-up care was 16.1 months. The average Injury Severity Score was 23. The average number of instrumented levels was 6.8. The focal kyphosis of the injury was reduced from a mean of 19.60 to 5.73 degrees (P<0.001), with an average progression of only 2.27 degrees (P=0.128) at final follow-up. Complications were limited to wound infections and occurred in 2 study participants. Neurologic status returned to normal in all patients with incomplete cord injuries. CONCLUSIONS FDI of the thoracic spine may be amendable to a uniform surgical approach with P/TPS. This procedure carried a relatively low complication rate and allowed for reduction and restoration of the posterior tension band with a biomechanically rigid construct.
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Comparative Biomechanical Analysis of an Improved Novel Pedicle Screw With Sheath and Bone Cement. ACTA ACUST UNITED AC 2007; 20:462-7. [DOI: 10.1097/bsd.0b013e318030d2d6] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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