A finite element study of a fractured tibia treated with a unilateral external fixator: The effects of the number of pins and cortical thickness |
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| Institution: | 1. Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran;2. Bone and Joint Diseases Research Center, Shiraz University of Medical Sciences, Shiraz, Iran;3. Institute of Fundamental Technological Research, Polish Academy of Sciences, Pawińskiego 5B, 02-106 Warsaw, Poland;1. Reconstructive Sciences Unit, School of Medical Sciences, Health Campus, Universiti Sains Malaysia, Kelantan, Malaysia;2. Department of Plastic Surgery, Hospital Universiti Sains Malaysia, Kelantan, Malaysia;3. Department of Pathology, School of Medical Sciences, Health Campus, Universiti Sains Malaysia, Kelantan, Malaysia;1. Department of, Institution of Clinical Sciences, Intervention and Technology (CLINTEC). Karolinska Institutet, Stockholm, Sweden;2. Unit of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet;3. Division of Orthopaedics, Karolinska University Hospital, Stockholm, Sweden;1. Medisch Spectrum Twente, Koningstraat 1, Enschede, KZ 7512, The Netherlands;2. OLVG Hospital, Oosterpark 9, Amsterdam, AC 1091, The Netherlands;3. LUMC Leiden and OLVG Hospital, Oosterpark 9, Amsterdam, AC 1091, The Netherlands;1. Research Service, VA Central Western Massachusetts Healthcare System, 421N Main, Leeds, MA 01053 USA;2. Department of Population and Quantitative Health Sciences, University of Massachusetts Medical School, 368 Plantation St, Worcester, MA 01655 USA;3. VA Salt Lake City Health Care System, 500 Foothill Blvd, Salt Lake City, UT 84148 USA;4. Department of Internal Medicine, Division of Epidemiology, University of Utah School of Medicine, 295 Chipeta Way, Salt Lake City, UT 84132 USA;5. Center for Mental Healthcare & Outcomes Research, Central Arkansas Veterans Healthcare System, 2200 Fort Roots Dr, North Little Rock, AR 72114 USA;6. Department of Psychiatry, University of Arkansas for Medical Sciences, 4301W Markham St, Little Rock, AR 72205 USA;7. South Texas Veterans Health Care System, 7400 Merton Minter Blvd, San Antonio, TX 78229 USA;8. Department of Population Health Sciences, Long School of Medicine, University of Texas Health San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78229 USA;9. United States Army Institute of Surgical Research, JBSA Fort Sam Houston, San Antonio, TX 78234 USA;10. Louisiana State University Health Science Center - New Orleans Department of Orthopaedic Surgery, New Orleans, LA USA;11. Geriatric Research, Education & Clinical Center, South Texas Veterans Health Care System, 7400 Merton Minter Blvd, San Antonio, TX 78229 USA;12. Department of Surgery, University of Texas Health San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78229 USA;13. Departments of Primary Care & Population Health and Medical Physiology, College of Medicine, Texas A&M Health, 2900 E 29th St, Bryan, TX 77802 USA;1. Registrar in Trauma & Orthopaedics, Royal Free London NHS Foundation Trust. London, United Kingdom;2. Registrar in Trauma & Orthopaedics., Barking, Havering & Redbridge University Hospitals NHS Trust. London, United Kingdom;3. Consultant Orthopaedic & Trauma Surgeon. University Hospitals Birmingham NHS Foundation Trust. Birmingham, United Kingdom;4. Consultant Orthopaedic & Trauma Surgeon. Royal Free London NHS Foundation Trust. London, United Kingdom;5. Consultant Paediatric Orthopaedic & Trauma Surgeon, University Hospitals Coventry and Warwickshire NHS Trust. Coventry, United Kingdom |
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| Abstract: | IntroductionIn the early stage of fracture fixation, the aim of a unilateral external fixator (UEF) to stimulate healing and maintain stability may be suppressed by using inadequate number of pins. Cortical thinning due to age or osteoporosis endangers a successful fracture fixation.Materials and methodsThis study evaluates the initial strength and stability of the fracture fixation and tissue differentiation under the influences of variable cortical thickness (5 mm to 1 mm) and variable number of pins (1 to 4 in each bone fragment). A finite element program was utilised to develop 20 three-dimensional models of simplified diaphyseal tibia with fracture callus fixed with UEF. A mechano-regulation code based on the deviatoric strain theory was written and applied to simulate tissue differentiation. The values of von Mises stress, interfragmentary strain (IFS), and fibrocartilage index (FCI) were evaluated.ResultsCortical thinning from 5 mm to 1 mm increased IFS and FCI by an average of 30.3% and 18.7%, respectively, and resulted in higher stresses in the UEF and bone. Using 1 pin in each bone fragment produced excessive IFS in the models with 1 mm, 2 mm and 3 mm cortical thickness. Inserting the second pin into the bone fragment could considerably reduce the IFS and fibrocartilaginous tissue formation in the fracture site and improve load transmission to the fixator. Whereas inserting the fourth pin could minimally affect the mechano-biological environment of healing.ConclusionsThis study suggests that initial instability due to cortical thinning can be efficiently alleviated by adding the number of pins up to 3 in a UEF; additionally, it may improve the knowledge about applying UEFs adequately stable, whilst promoting inclination toward endochondral ossification, simultaneously. |
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