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Liu S, Lu L, Chen T, Liu Y, Wei D, Miao J, Yu D, Fu X. In vivo axial load-share ratio measurement using a novel hexapod system for safe external fixator removal. BMC Musculoskelet Disord 2024; 25:353. [PMID: 38724941 PMCID: PMC11080187 DOI: 10.1186/s12891-024-07440-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2024] [Accepted: 04/12/2024] [Indexed: 05/13/2024] Open
Abstract
BACKGROUND External fixation is widely used in the treatment of traumatic fractures; however, orthopedic surgeons encounter challenges in deciding the optimal time for fixator removal. The axial load-share ratio (LS) of the fixator is a quantitative index to evaluate the stiffness of callus healing. This paper introduces an innovative method for measuring the LS and assesses the method's feasibility and efficacy. Based on a novel hexapod LS-measurement system, the proposed method is to improve the convenience and precision of measuring LS in vivo, hence facilitating the safe removal of external fixators. METHODS A novel hexapod system is introduced, including its composition, theoretical model, and method for LS measurement. We conducted a retrospective study on 82 patients with tibial fractures treated by the Taylor Spatial Frame in our hospital from September 2018 to June 2020, of which 35 took LS measurements with our novel method (Group I), and 47 were with the traditional method (Group II). The external fixator was removed when the measurement outcome (LS < 10%) was consistent with the surgeon's diagnosis based on the clinical and radiological assessment (bone union achieved). RESULTS No significant difference was found in the fracture healing time (mean 25.3 weeks vs. 24.9 weeks, P > 0.05), frame-wearing duration (mean 25.5 weeks vs. 25.8 weeks, P > 0.05), or LS measurement frequency (mean 1.1 times vs. 1.2 times, P > 0.05). The measurement system installation time in Group I was significantly shorter compared to Group II (mean 14.8 min vs. 81.3 min, P < 0.001). The LS value of the first measurement in Group I was lower than that of Group II (mean 5.1% vs. 6.9%, P = 0.011). In Group I, the refracture rate was 0, but in Group II it was 4.3% (2/47, P > 0.05). CONCLUSION The novel hexapod LS-measurement system and involved method demonstrated enhanced convenience and precision in measuring the LS of the external fixator in vivo. The LS measurement indicates the callus stiffness of fracture healing, and is applicable to evaluate the safety of removing the fixator. Consequently, it is highly recommended for widespread adoption in clinical practice.
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Affiliation(s)
- Sida Liu
- School of Mechanical Engineering, Tianjin University, Tianjin, China
- Department of Radiotherapy, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China
- Department of Orthopedics, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China
| | - Lin Lu
- School of Mechanical Engineering, Tianjin University, Tianjin, China
- Department of Radiotherapy, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China
- Department of Orthopedics, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China
| | - Tao Chen
- School of Mechanical Engineering, Tianjin University, Tianjin, China
- Department of Radiotherapy, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China
- Department of Orthopedics, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China
| | - Yanshi Liu
- Department of Orthopedics, The Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, China
| | - Dong Wei
- Department of Orthopedics Surgery, Tianjin Academy Traditional Chinese Medicine Affiliated Hospital, Tianjin, China
| | - Jun Miao
- Department of Spine Surgery, Tianjin Hospital, Tianjin, China.
| | - Defu Yu
- Department of Orthopedics, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China.
| | - Xuefei Fu
- Department of Orthopedics, Anhui No.2 Provincial People's Hospital, Hefei, Anhui, China.
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Ganse B, Orth M, Roland M, Diebels S, Motzki P, Seelecke S, Kirsch SM, Welsch F, Andres A, Wickert K, Braun BJ, Pohlemann T. Concepts and clinical aspects of active implants for the treatment of bone fractures. Acta Biomater 2022; 146:1-9. [PMID: 35537678 DOI: 10.1016/j.actbio.2022.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 04/24/2022] [Accepted: 05/02/2022] [Indexed: 12/17/2022]
Abstract
Nonunion is a complication of long bone fractures that leads to disability, morbidity and high costs. Early detection is difficult and treatment through external stimulation and revision surgery is often a lengthy process. Therefore, alternative diagnostic and therapeutic options are currently being explored, including the use of external and internal sensors. Apart from monitoring fracture stiffness and displacement directly at the fracture site, it would be desirable if an implant could also vary its stiffness and apply an intervention to promote healing, if needed. This could be achieved either by a predetermined protocol, by remote control, or even by processing data and triggering the intervention itself (self-regulated 'intelligent' or 'smart' implant). So-called active or smart materials like shape memory alloys (SMA) have opened up opportunities to build active implants. For example, implants could stimulate fracture healing by active shortening and lengthening via SMA actuator wires; by emitting pulses, waves, or electromagnetic fields. However, it remains undefined which modes of application, forces, frequencies, force directions, time durations and periods, or other stimuli such implants should ideally deliver for the best result. The present paper reviews the literature on active implants and interventions for nonunion, discusses possible mechanisms of active implants and points out where further research and development are needed to build an active implant that applies the most ideal intervention. STATEMENT OF SIGNIFICANCE: Early detection of delays during fracture healing and timely intervention are difficult due to limitations of the current diagnostic strategies. New diagnostic options are under evaluation, including the use of external and internal sensors. In addition, it would be desirable if an implant could actively facilitate healing ('Intelligent' or 'smart' implant). Implants could stimulate fracture healing via active shortening and lengthening; by emitting pulses, waves, or electromagnetic fields. No such implants exist to date, but new composite materials and alloys have opened up opportunities to build such active implants, and several groups across the globe are currently working on their development. The present paper is the first review on this topic to date.
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Martyniuk B, Morasiewicz P, Wudarczyk S, Dragan SF, Filipiak J. The impact of configuration of the Ilizarov fixator on its stiffness and the degree of loading of distraction rods. Clin Biomech (Bristol, Avon) 2019; 63:79-84. [PMID: 30849649 DOI: 10.1016/j.clinbiomech.2019.02.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Revised: 01/19/2019] [Accepted: 02/26/2019] [Indexed: 02/07/2023]
Abstract
BACKGROUND The mechanical parameters of the Ilizarov fixator are influenced by many factors related to its spatial configuration. The aim of this study was to experimentally evaluate the impact of the type of implant and the number of distraction rods on the uniformity of loading of distraction rods and stiffness coefficients of the Ilizarov fixator. METHODS The tests were carried out on a physical model. The model was mounted in a universal loading station MTS 858 Mini Bionix. Forces in distraction rods are measured with the use of strain gauge force transducers. Displacements of bone fragments were measured by means of digital image correction. FINDINGS In the case of a fixator with 3 distraction rods, configuration of implants has no statistically significant effect on the forces occurring in distraction rods. In the case of a fixator with 4 distraction rods, there are statistically significant differences in the forces in distraction rods. The highest transverse stiffness coefficients occurs in the system with 4 distraction rods and the configuration of 1K1S implants, while the smallest transverse stiffness coefficients occurs in the fixator with 4 distraction rods and the configuration of 0K1S implants. INTERPRETATION Based on the results of experiments on the physical model, we observed an asymmetry in the distribution of forces transmitted through distraction rods. The configuration with 3 distraction rods provides more uniform distribution of forces in distraction rods and reduces the impact of the implant configuration on transverse stiffness coefficients. The use of a configurations with 4 rods may be advantageous when we want to obtain greater transverse stiffness coefficients of a system consisting of the fixator and fragments of the lengthened bone.
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Affiliation(s)
- Bartosz Martyniuk
- Wrocław University of Science and Technology, Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Łukasiewicza 7/9, 50-371 Wrocław, Poland
| | - Piotr Morasiewicz
- Wrocław Medical University, Department and Clinic of Orthopaedic and Traumatologic Surgery, Borowska 213, 50-556 Wrocław, Poland.
| | - Sławomir Wudarczyk
- Wrocław University of Science and Technology, Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Łukasiewicza 7/9, 50-371 Wrocław, Poland
| | - Szymon Feliks Dragan
- Wrocław Medical University, Department and Clinic of Orthopaedic and Traumatologic Surgery, Borowska 213, 50-556 Wrocław, Poland
| | - Jarosław Filipiak
- Wrocław University of Science and Technology, Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Łukasiewicza 7/9, 50-371 Wrocław, Poland
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Zhao X, Li J, Chen Y, Tao C, Ji R. Investigation of load transfer process between external fixator and bone model by experimental and finite element methods. J Appl Biomater Funct Mater 2019; 17:2280800019826512. [PMID: 30803304 DOI: 10.1177/2280800019826512] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
INTRODUCTION: Unilateral external fixators are widely used in orthopedics to stabilize fractured bones and to treat limb deformities. One of the main problems is that it is difficult to detect healing status. In addition, whether load transfer progress between the fixator and bone model are the same under axial, torsional, and bending loads has not been studied. METHODS: Therefore the main purpose of this study was to detect the load transfer process between the fixator and a bone model by measuring strains on the fixator-bone system during four healing states using experimental and finite element methods. In the experimental method, 20 strain gauges were used to measure strain on the fixator and bone model under three load conditions. Polyacetal slice models with different material properties were used to simulate the callus model during four growth states. RESULTS: The results indicate that strain on the bone model increased and strain on the fixator parts decreased with maturation of the callus under axial, bending, and torsional loads. Although all curves showed a similar changing trend, they were slightly different under the three loads. DISCUSSION AND CONCLUSIONS: This study provides a useful method to monitor the fracture healing process, and identifies the healing endpoint, detects healing status, and provides useful information for the orthopedist.
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Affiliation(s)
- Xia Zhao
- 1 Beijing University of Technology, Beijing, China
| | - Jianfeng Li
- 1 Beijing University of Technology, Beijing, China
| | - Ying Chen
- 1 Beijing University of Technology, Beijing, China
| | - Chunjing Tao
- 2 National Research Center for Rehabilitation Technical Aids, Beijing, China
| | - Run Ji
- 2 National Research Center for Rehabilitation Technical Aids, Beijing, China
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Li J, Zhao X, Hu X, Tao C, Ji R. A finite element analysis for monitoring the healing progression of fixator-bone system under three loading conditions. Biomed Mater Eng 2018; 29:473-483. [PMID: 30282344 DOI: 10.3233/bme-181003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND Unilateral external fixators are widely used in orthopedics to stabilize fractured bones and in the treatment of limb deformities. The main value for evaluation of mechanical stability of the external fixator is fixator stiffness. The fixator stiffness is an important factor as it will influence the biomechanical environment to which fixator and regenerating tissues are exposed. OBJECTIVE The main objective of this work was to monitor the transmission of stress and the change of displacement generated in fixator-bone system under three loading conditions during healing process. METHODS In this study, a finite element model with changing Young's modulus of the callus is established, finite element analysis was used to investigating stress and deformation of fixator-bone system caused by axial load, torsional load and bending load during three healing stages. RESULTS The results reveal that at different healing stages, stress distribution between the fixator and fractured bone is different, the position of displacement is mainly concentrated in the fracture site and proximal bone and with the increase of healing time, the deformation decreased. CONCLUSIONS This work helps orthopedic doctors to monitor the progression of fracture healing and determine the appropriate time for removal of a fixation device and provide useful information.
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Affiliation(s)
- Jianfeng Li
- Beijing University of Technology, Beijing, China
| | - Xia Zhao
- Beijing University of Technology, Beijing, China
| | - XiaoJie Hu
- Beijing University of Technology, Beijing, China
| | - Chunjing Tao
- National Research Center for Rehabilitation Technical Aids, Beijing, China
| | - Run Ji
- National Research Center for Rehabilitation Technical Aids, Beijing, China
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MacLeod AR, Pankaj P. Pre-operative planning for fracture fixation using locking plates: device configuration and other considerations. Injury 2018; 49 Suppl 1:S12-S18. [PMID: 29929685 DOI: 10.1016/s0020-1383(18)30296-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Most locked plating failures are due to inappropriate device configuration for the fracture pattern. Several studies cite screw positioning variables such as the number and spacing of screws as responsible for occurrences of locking plate breakage, screw loosening, and peri-prosthetic re-fracture. It is also widely accepted that inappropriate device stiffness can inhibit or delay healing. Careful preoperative planning is therefore critical if these failures are to be prevented. This study examines several variables which need to be considered when optimising a locking plate fixation device for fracture treatment including: material selection; screw placement; the effect of the fracture pattern; and the bone-plate offset. We demonstrate that device selection is not straight-forward as many of the variables influence one-another and an identically configured device can perform very differently depending upon the fracture pattern. Finally, we summarise the influence of some of the key parameters and the influence this can have on the fracture healing environment and the stresses within the plate in a flowchart.
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Affiliation(s)
| | - Pankaj Pankaj
- School of Engineering, The University of Edinburgh, UK.
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Li J, Zhao X, Hu X, Tao C, Ji R. A theoretical analysis and finite element simulation of fixator-bone system stiffness on healing progression. J Appl Biomater Funct Mater 2018; 16:115-125. [PMID: 29582693 DOI: 10.1177/2280800017750357] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
INTRODUCTION The unilateral external fixator has become a quick and easy application for fracture stabilization of the extremities; the main value for evaluation of mechanical stability of the external fixator is stiffness. The stiffness property of the external fixator affects the local biomechanical environment of fractured bone. METHODS In this study, a theoretical model with changing Young's modulus of the callus is established by using the Castigliano's theory, investigating compression stiffness, torsional stiffness and bending stiffness of the fixator-bone system during the healing process. The effects of pin deviation angle on three stiffness methods are also investigated. In addition, finite element simulation is discussed regarding the stress distribution between the fixator and bone. RESULTS The results reveal the three stiffness evaluation methods are similar for the fixator-bone system. Finite element simulation shows that with increased healing time, the transmission of the load between the fixator and bone are different. In addition, the finite element analyses verify the conclusions obtained from the theoretical model. CONCLUSIONS This work helps orthopedic doctors to monitor the progression of fracture healing and determine the appropriate time for removal of a fixation device and provide important theoretical methodology.
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Affiliation(s)
- Jianfeng Li
- 1 College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing, China
| | - Xia Zhao
- 1 College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing, China
| | - Xiaojie Hu
- 1 College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing, China
| | - Chunjing Tao
- 2 National Research Center for Rehabilitation Technical Aids, Beijing, China
| | - Run Ji
- 2 National Research Center for Rehabilitation Technical Aids, Beijing, China
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MacLeod A, Simpson AHRW, Pankaj P. Experimental and numerical investigation into the influence of loading conditions in biomechanical testing of locking plate fracture fixation devices. Bone Joint Res 2018; 7:111-120. [PMID: 29363522 PMCID: PMC5805837 DOI: 10.1302/2046-3758.71.bjr-2017-0074.r2] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Objectives Secondary fracture healing is strongly influenced by the stiffness of the bone-fixator system. Biomechanical tests are extensively used to investigate stiffness and strength of fixation devices. The stiffness values reported in the literature for locked plating, however, vary by three orders of magnitude. The aim of this study was to examine the influence that the method of restraint and load application has on the stiffness produced, the strain distribution within the bone, and the stresses in the implant for locking plate constructs. Methods Synthetic composite bones were used to evaluate experimentally the influence of four different methods of loading and restraining specimens, all used in recent previous studies. Two plate types and three screw arrangements were also evaluated for each loading scenario. Computational models were also developed and validated using the experimental tests. Results The method of loading was found to affect the gap stiffness strongly (by up to six times) but also the magnitude of the plate stress and the location and magnitude of strains at the bone-screw interface. Conclusions This study demonstrates that the method of loading is responsible for much of the difference in reported stiffness values in the literature. It also shows that previous contradictory findings, such as the influence of working length and very large differences in failure loads, can be readily explained by the choice of loading condition. Cite this article: A. MacLeod, A. H. R. W. Simpson, P. Pankaj. Experimental and numerical investigation into the influence of loading conditions in biomechanical testing of locking plate fracture fixation devices. Bone Joint Res 2018;7:111–120. DOI: 10.1302/2046-3758.71.BJR-2017-0074.R2.
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Affiliation(s)
| | - A H R W Simpson
- Department of Orthopaedic Surgery, University of Edinburgh, Chancellor's Building, 49 Little France Crescent, Old Dalkeith Road, Edinburgh EH16 4SB, UK
| | - P Pankaj
- The University of Edinburgh, School of Engineering, Institute for Bioengineering, Faraday Building, Edinburgh EH9 3DW, UK
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MacLeod AR, Simpson AHRW, Pankaj P. Age-related optimization of screw placement for reduced loosening risk in locked plating. J Orthop Res 2016; 34:1856-1864. [PMID: 26872689 DOI: 10.1002/jor.23193] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 01/28/2016] [Indexed: 02/04/2023]
Abstract
When using locked plating for bone fracture fixation, screw loosening is reported as one of the most frequent complications and is commonly attributed to an incorrect choice of screw configuration. Choosing a patient-optimized screw configuration is not straightforward as there are many interdependent variables that affect device performance. The aim of the study was to evaluate the influence that locking screw configuration has on loosening risk and how this is influenced by bone quality. This study uses finite element models that incorporate cortical bone heterogeneity, orthotropy, and geometrical nonlinearity to examine the effect of screw configuration on variables associated with loosening and interfragmentary motion. Strain levels within the bone were used as indicators of regions that may undergo loosening. The study found that, in healthy bone under axial loading, the most important variables influencing strain levels within the bone were the size of the bridging span (working length) and the plate rigidity. Unlike healthy bone, osteoporotic bone was found to be particularly sensitive to the spacing of the screws within the plate. Using two empty screw holes between the screws closest to the fracture was found to reduce the strain levels at the first screw by 49% in osteoporotic bone (compared to only 2.4% in healthy bone). The study also found that under torsional loading the total number of screws used was the most important variable with a 59% reduction in the strain around the screws closest to the fracture when using six rather than four screws in osteoporotic bone. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1856-1864, 2016.
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Affiliation(s)
- Alisdair R MacLeod
- School of Engineering, The University of Edinburgh, Edinburgh, EH9 3JL, Scotland, United Kingdom
| | - A Hamish R W Simpson
- Department of Orthopaedic Surgery, The University of Edinburgh, Edinburgh, EH16 4SU, Scotland, United Kingdom
| | - Pankaj Pankaj
- School of Engineering, The University of Edinburgh, Edinburgh, EH9 3JL, Scotland, United Kingdom
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Jabbar Y, Khaleel A. Experimental model for controlling shear using the Ilizarov frame. Clin Biomech (Bristol, Avon) 2015; 30:995-1001. [PMID: 26194448 DOI: 10.1016/j.clinbiomech.2015.06.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Revised: 06/22/2015] [Accepted: 06/23/2015] [Indexed: 02/07/2023]
Abstract
OBJECTIVE This study has been designed to ascertain whether a standard configuration Ilizarov tibial frame can control shear motion at the fracture site of an oblique fracture within acceptable limits for axial micro-motion, and therefore promote bony union. If not, are there simple modifications to the frame design that can achieve this? METHODS Four Ilizarov frame designs were tested on a load test rig. Fracture site shear displacement was measured using a clip gauge attached to an automated data recording system. FINDINGS The standard Ilizarov frame allowed 4mm of fracture site displacement at 340N of load. Our fourth frame design, the locked olive frame, allowed a maximum of 0.61mm displacement at 700N. INTERPRETATION This is one of only two studies to look at circular frame fracture site control in oblique fractures. This is the only study to characterise Ilizarov frame stiffness in oblique fractures. We have shown that the standard Ilizarov frame design is inadequate for control of oblique fractures in this mechanical model. Our data show that with the application of simple principles, the Ilizarov frame can be modified to provide better fracture site control. These frame designs can be applied clinically to reduce fracture site shear motion in oblique fractures, resulting in improved union rates.
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Affiliation(s)
- Yaser Jabbar
- Dept. of Orthopaedics, Chelsea and Westminster Hospital, Fulham Road, London, SW10 9NH, UK; Cardiff University, Cardiff, Wales, United Kingdom.
| | - Arshad Khaleel
- Dept. Of Orthopaedics, St. Peter's Hospital, Guildford Road, Chertsey, Surrey, KT16 0PZ, United Kingdom.
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Computational modelling of ovine critical-sized tibial defects with implanted scaffolds and prediction of the safety of fixator removal. J Mech Behav Biomed Mater 2015; 44:133-46. [DOI: 10.1016/j.jmbbm.2015.01.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 01/05/2015] [Accepted: 01/07/2015] [Indexed: 11/23/2022]
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MacLeod AR, Simpson AHRW, Pankaj P. Reasons why dynamic compression plates are inferior to locking plates in osteoporotic bone: a finite element explanation. Comput Methods Biomech Biomed Engin 2014; 18:1818-25. [PMID: 25473732 DOI: 10.1080/10255842.2014.974580] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
While locking plate fixation is becoming increasingly popular for complex and osteoporotic fractures, for many indications compression plating remains the standard choice. This study compares the mechanical behaviour of the more recent locking compression plate (LCP) device, with the traditional dynamic compression plates (DCPs) in bone of varying quality using finite element modelling. The bone properties considered include orthotropy, inhomogeneity, cortical thinning and periosteal apposition associated with osteoporosis. The effect of preloads induced by compression plating was included in the models. Two different fracture scenarios were modelled: one with complete reduction and one with a fracture gap. The results show that the preload arising in DCPs results in large principal strains in the bone all around the perimeter of the screw hole, whereas for LCPs large principal strains occur primarily on the side of the screw proximal to the load. The strains within the bone produced by the two screw types are similar in healthy bone with a reduced fracture gap; however, the DCP produces much larger strains in osteoporotic bone. In the presence of a fracture gap, the DCP results in a considerably larger region with high tensile strains and a slightly smaller region with high compressive strains. These findings provide a biomechanical basis for the reported improved performance of locking plates in poorer bone quality.
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Affiliation(s)
- Alisdair R MacLeod
- a School of Engineering, The University of Edinburgh , Edinburgh EH9 3JL, Scotland , UK
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Roseiro LM, Neto MA, Amaro A, Leal RP, Samarra MC. External fixator configurations in tibia fractures: 1D optimization and 3D analysis comparison. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2013; 113:360-370. [PMID: 24176414 DOI: 10.1016/j.cmpb.2013.09.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2012] [Revised: 09/11/2013] [Accepted: 09/23/2013] [Indexed: 06/02/2023]
Abstract
The use of external fixation devices in orthopedic surgery is very common in open tibial fractures. A properly applied fixator may improve the healing process while one improperly applied might delay the healing process. The several external fixator systems used in clinical today, can be categorized into uniplanar-unilateral, uniplanar-bilateral, biplanar and multiplanar. The stability on the fracture focus and, therefore, the fracture healing process, is related with the type of external fixator configuration that is selected. The aim of this study is to discuss the principles for the successful application of unilateral-uniplanar external fixation, the assembly of its components, for the case of a transverse fractures using computational models. In this context, the fixation stiffness characteristics are evaluated using a simplified 1D finite element model for the tibia and external fixator. The beams are modeled with realistic cross-sectional geometry and material properties instead of a simplified model. The VABS (the Variational Asymptotic Beam Section analysis) methodology is used to compute the cross-sectional model for the generalized Timoshenko model, which was embedded in the finite element solver FEAP. The use of Timoshenko beam theory allows accounting for several kinds of loads, including torsion moments. Optimal design is performed with respect to the assembly of fixator components using a genetic algorithm. The optimization procedure is based on the evaluation of an objective function, which is dependent on the displacement at the fracture focus. The initial and optimal results are compared by performing a 3D analysis, for which different three-dimensional finite element models are created. The geometrical model of a tibia is created on the basis of data acquired by CAT scan, made for a healthy tibia of a 22 year old male. The 3D comparison of the 1D optimal results show a clear improvement on the objective function for the several load cases and, therefore, it is shown that appropriate selection of the external fixator geometrical features can lead to an improvement on the stability of the external fixator. The results obtained show that the optimal position of the side beam and the first pin should be as close as possible to the bone interface and as close as possible to the fracture focus, respectively. Concerning the second pin, it should be placed away from the first pin in case of flexion loads, to axial and torsion loads the second pin should be placed near the first pin.
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Affiliation(s)
- Luis M Roseiro
- Departamento de Engenharia Mecânica - Instituto Superior de Engenharia de Coimbra, Rua Pedro Nunes - Quinta da Nora, 3030-199 Coimbra, Portugal.
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Donaldson FE, Pankaj P, Simpson AHRW. Bone properties affect loosening of half-pin external fixators at the pin-bone interface. Injury 2012; 43:1764-70. [PMID: 22841532 DOI: 10.1016/j.injury.2012.07.001] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 01/17/2012] [Accepted: 07/02/2012] [Indexed: 02/02/2023]
Abstract
INTRODUCTION Local bone yielding at the pin-bone interface of external fixation half-pins has been known to initiate fixator loosening. Deterioration of bone properties due to ageing and disease can lead to an increase in the risk of pin loosening. This study determines the extent, locations and mechanics of bone yielding for unilateral external fixation systems at the tibial midshaft with changes in age-related bone structure and properties. The study also evaluates the effect of the number of pins used in the fixation system and use of titanium pins (in place of steel) on bone yielding. METHODS We employ nonlinear finite element (FE) simulations. Strain-based plasticity is used to simulate bone yielding within FE analyses. Our analyses also incorporate contact behaviour at pin-bone interfaces, orthotropic elasticity and periosteal-endosteal variation of bone properties. RESULTS The results show that peri-implant yielded bone volume increases by three times from young to old-aged cases. The use of three, rather than two half-pins (on either side of the fracture), reduces the volume of yielded bone by 80% in all age groups. The use of titanium half-pins resulted in approximately 60-65% greater volumes of yielded bone. CONCLUSIONS We successfully simulate half-pin loosening at the bone-implant interface which has been found to occur clinically. Yielding across the full cortical thickness may explain the poor performance of these devices for old-aged cases. The models are able to identify patients particularly at risk of half-pin loosening, who may benefit from alternative fixator configurations or techniques such as those using pre-tensioned fine wires.
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Affiliation(s)
- Finn E Donaldson
- School of Engineering, The University of Edinburgh, Edinburgh, UK
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Sternick MB, Dallacosta D, Bento DÁ, do Reis ML. RELATIONSHIP BETWEEN RIGIDITY OF EXTERNAL FIXATOR AND NUMBER OF PINS: COMPUTER ANALYSIS USING FINITE ELEMENTS. Rev Bras Ortop 2012; 47:646-50. [PMID: 27047879 PMCID: PMC4799440 DOI: 10.1016/s2255-4971(15)30017-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Accepted: 02/09/2012] [Indexed: 11/29/2022] Open
Abstract
Objective: To analyze the rigidity of a platform-type external fixator assembly, according to different numbers of pins on each clamp. Methods: Computer simulation on a large-sized Cromus dynamic external fixator (Baumer SA) was performed using a finite element method, in accordance with the standard ASTM F1541. The models were generated with approximately 450,000 quadratic tetrahedral elements. Assemblies with two, three and four Schanz pins of 5.5 mm in diameter in each clamp were compared. Every model was subjected to a maximum force of 200 N, divided into 10 sub-steps. For the components, the behavior of the material was assumed to be linear, elastic, isotropic and homogeneous. For each model, the rigidity of the assembly and the Von Mises stress distribution were evaluated. Results: The rigidity of the system was 307.6 N/mm for two pins, 369.0 N/mm for three and 437.9 N/mm for four. Conclusion: The results showed that four Schanz pins in each clamp promoted rigidity that was 19% greater than in the configuration with three pins and 42% greater than with two pins. Higher tension occurred in configurations with fewer pins. In the models analyzed, the maximum tension occurred on the surface of the pin, close to the fixation area.
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Affiliation(s)
| | - Darlan Dallacosta
- Mechanical Engineer and MSc in Mechanical Engineering with emphasis on Biomechanics, SCiTec, Florianópolis, SC, Brazil
| | - Daniela Águida Bento
- Mechanical Engineer and PhD in Mechanical Engineering with emphasis on Biomechanics, Department of Metal Mechanics, Federal Institute of Education, Science and Technology of Santa Catarina (IF-SC), Florianópolis, SC, Brazil
| | - Marcelo Lemos do Reis
- Orthopedist and MSc in Medical Sciences, University Hospital of the Federal University of Santa Catarina (UFSC), Florianópolis, SC, Brazil
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MacLeod AR, Pankaj P, Simpson AHR. Does screw–bone interface modelling matter in finite element analyses? J Biomech 2012; 45:1712-6. [DOI: 10.1016/j.jbiomech.2012.04.008] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Revised: 04/04/2012] [Accepted: 04/05/2012] [Indexed: 10/28/2022]
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Donaldson FE, Pankaj P, Simpson AHRW. Investigation of factors affecting loosening of Ilizarov ring-wire external fixator systems at the bone-wire interface. J Orthop Res 2012; 30:726-32. [PMID: 22042453 DOI: 10.1002/jor.21587] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Accepted: 10/06/2011] [Indexed: 02/04/2023]
Abstract
The potential for peri-implant bone yielding and subsequent loosening of Ilizarov ring-wire external fixation systems was investigated using non-linear finite element (FE) analyses. A strain-based plasticity model was employed to simulate bone yielding. FE models also incorporated contact behavior at the wire-bone interface, orthotropic elasticity, and periosteal-endosteal variation of bone properties. These simulations were used to determine the extent and location of yielding with change in age-related bone structure and properties for the bone-Ilizarov construct at the tibial midshaft. At critical wire-bone interfaces, the predicted volume of yielded bone with four wires (on either side of the fracture) was ∼40% of that with two wires. Old-aged cases showed considerably greater bone yielding at the wire-bone interface than young cases (1.7-2.2 times greater volumes of yielded bone). The volume of yielded bone at all wire-bone interfaces decreased with an increase in wire pre-tension. The absence of continuous through-thickness yielding offers an explanation for the clinical observation that Ilizarov ring-wire fixation can provide stable fracture fixation even in bone with high porosity.
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Affiliation(s)
- Finn E Donaldson
- School of Engineering, The University of Edinburgh, Edinburgh, United Kingdom
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Wang X, Nyman J, Dong X, Leng H, Reyes M. Fundamental Biomechanics in Bone Tissue Engineering. ACTA ACUST UNITED AC 2010. [DOI: 10.2200/s00246ed1v01y200912tis004] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Eberle S, Bauer C, Gerber C, von Oldenburg G, Augat P. The stability of a hip fracture determines the fatigue of an intramedullary nail. Proc Inst Mech Eng H 2009; 224:577-84. [DOI: 10.1243/09544119jeim664] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The purpose of this study was to address the question of how the stability of a proximal hip fracture determines the fatigue and failure mechanism of an intramedullary implant. To answer this question, mechanical experiments and finite element simulations with two different loading scenarios were conducted. The two load scenarios differed in the mechanical support of the fracture by an artificial bone sleeve, representing the femoral head and neck. The experiments confirmed that an intramedullary nail fails at a lower load in an unstable fracture situation in the proximal femur than in a stable fracture. The nails with an unstable support failed at a load 28 per cent lower than the nails with a stable support by the femoral neck. Hence, the mechanical support of a fracture is crucial to the fatigue failure of an implant. The simulation showed why the fatigue fracture of the nail starts at the aperture of the lag screw. It is the location of the highest von Mises stress, which is the failure criterion for ductile materials.
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Affiliation(s)
- S Eberle
- Institute of Biomechanics, Trauma Center Murnau, Murnau, Germany
| | - C Bauer
- Stryker Osteosynthesis, Schoenkirchen/Kiel, Germany
| | - C Gerber
- Stryker Osteosynthesis, Schoenkirchen/Kiel, Germany
| | | | - P Augat
- Institute of Biomechanics, Trauma Center Murnau, Murnau, Germany
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De Kesel R, Burny F, Schuind F. Mini external fixation for hand fractures and dislocations: The current state of the art. Hand Clin 2006; 22:307-15. [PMID: 16843797 DOI: 10.1016/j.hcl.2006.02.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
External fixation devices for the hand provide a versatile approach to various hand injuries. Some fractures and dislocations urge the use of an external minifixation; in other fractures, external minifixation must be seen as an alternative or companion to other methods of hand stabilization. MiniFix is useful to maintain or restore hand function and hand anatomy.
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Affiliation(s)
- Renata De Kesel
- Department of Orthopaedics and Traumatology, Cliniques Universitaires de Bruxelles, Hôpital Erasme, ULB 808 Route de Lennik 1070, Brussels, Belgium
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