Revising a loosened cancellous screw with a larger screw does not restore original pull-out strength – A biomechanical study |
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| Institution: | 1. Department of Orthopaedic Surgery, Woodlands Health, Singapore;2. School of Mechanical & Aerospace Engineering, College of Engineering, Nanyang Technological University, Singapore;3. Department of Orthopaedic Surgery, Khoo Teck Puat Hospital, Singapore;1. University of Cologne, Faculty of Medicine, Department of Orthopedic and Trauma Surgery, Cologne, Germany;2. Department of Anesthesia, Heiliggeist Hospital, Cologne, Germany;3. Department of Anatomy, University of Cologne, Cologne, Germany;1. Amsterdam UMC, Vrije Universiteit Amsterdam, Department of Rehabilitation Medicine, Amsterdam Movement Sciences, de Boelelaan 1117, Amsterdam, the Netherlands;2. Amsterdam UMC, University of Amsterdam, Medical Imaging Quantification Center (MIQC), Department of Radiology and Nuclear Medicine, Amsterdam Movement Sciences, Meibergdreef 9, Amsterdam, the Netherlands;3. Centre for Health, Exercise and Sports Medicine, Department of Physiotherapy, School of Health Sciences, The University of Melbourne, Melbourne, VIC, Australia;4. Delft University of Technology, Department of Biomechanical Engineering, Delft, the Netherlands;5. Erasmus Medical Center, Department of Orthopedics, Rotterdam, the Netherlands;6. Amsterdam Rehabilitation Research Center, Reade, Amsterdam, the Netherlands;7. Centre of Expertise Urban vitality, Center of Applied Research, Faculty of Health, Amsterdam University of Applied Sciences, Amsterdam, the Netherlands;1. Research Centre of Movement Science, University of Iceland, Sæmundargata 2, 102 Reykjavík, Iceland;2. Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, School of Engineering and Natural Sciences, University of Iceland, Sæmundargata 2, 102 Reykjavík, Iceland;3. Össur hf., Grjótháls 5, 110 Reykjavik, Iceland;1. AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland;2. Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gußhausstraße 27-29, A-1040 Vienna, Austria;3. Institute for Surgical Technology & Biomechanics, Universität Bern, Stauffacherstrasse 78, CH-3014 Bern, Switzerland;4. Department of Trauma Surgery, Medical University of Vienna, Austria;5. Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria;1. Third Faculty of Medicine, Charles University, Prague, Ruska 2411/87, 100 00 Praha 10-Vinohrady, Czech Republic;2. Regional Hospital in Liberec, Husova 10, Liberec 46001, Czech Republic;3. Colleague of Polytechnics Jihlava, Tolsteho 1556, Jihlava 58601, Czech Republic;4. Technical University of Liberec, Studentska 2, Liberec 46117, Czech Republic;1. Department of Orthopedics, Huashan Hospital, Fudan University, 12 Middle Wulumuqi Road, Shanghai 200040, China;2. Department of Orthopedics, Huashan Hospital North, Fudan University, 108 Luxiang Road, Shanghai 200040, China |
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| Abstract: | BackgroundCancellous screw fixation is often used in fracture fixation. When this screw is over-tightened, damage to the bone and other non-linear processes such as fracture and construct failure would be involved. The objectives of this study were (1) to determine the reduction in pull-out strength when a cancellous screw spins and (2) to determine how much pull-out strength can be restored by revising with a larger diameter screw.MethodsA biomechanical study using synthetic polyurethane foam (320 kg/m3) was performed to assess (1) the pull-out strength of a 6.5 mm cancellous screw, (2) the pull-out strength of a loosened 6.5 mm cancellous screw and (3) the pull-out strength of a loosened 6.5 mm cancellous screw revised with a 7.3 mm cancellous screw.FindingsThe baseline pull-out strength of the 6.5 mm cancellous screw was 2213.91 ± 200.51 N. There was a 79.1% (463.79 ± 99.95 N) reduction in pull-out strength once spinning occurs (p = 0.027). When a spinning 6.5 mm cancellous screw was revised to a 7.3 mm cancellous screw, the pull-out strength increased to 1313.65 ± 93.23 N, 59.3% of the baseline pull-out strength (2213.91 ± 200.51 N) (p = 0.027).IntepretationA loosened 6.5 mm cancellous screw results in a 79.1% reduction in pull-out strength. Revising a loosened cancellous screw by inserting a larger 7.3 mm diameter screw partially improves the pull-out strength to 59.3% of the baseline. Surgeons should consider the use of “two-finger tight” torque when inserting a screw to avoid stripping. |
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