Influence of pilot hole diameter in cancellous screw fixation in a reduced density animal bone model |
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| Institution: | 1. Medical Student, School of Medicine, Stanford University, Palo Alto, CA;2. Medical Student, School of Medicine, University of California San Diego, La Jolla, CA;3. Assistant Professor, School of Medicine, University of California San Francisco, San Francisco, CA;4. Surgeon, Department of Anatomy and Orthopedics, University of California San Francisco, San Francisco, CA;5. Clinical Assistant Professor, Department of Orthopedic Surgery, Stanford University Medical Center, Palo Alto, CA;1. Chair of Fluid Mechanics and Institute of Aerodynamics, RWTH Aachen University, Wüllnerstr. 5a, 52062 Aachen, Germany;2. Department of Plant Physiology (Bio III), RWTH Aachen University, Worringer Weg 1, 52074 Aachen, Germany |
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| Abstract: | BackgroundScrew fixation in osteoporotic bone is clinically challenging. Screw failure rates are growing due to an increasing prevalence of osteoporosis. To address this, biomechanical models are needed to recreate the bone clinically encountered alongside the development of new operative techniques. The first aim of this study was to test whether the use of a smaller than recommended pilot-hole diameter improved pull-out strength for cancellous screws, with the second aim to create a model of low-density porcine bone for biomechanical testing.MethodsThirty porcine tibiae were cut into transverse metaphyseal sections of 20 mm thickness. Bone density was altered using 0.15 M Hydrochloric acid, and measured and pre- and post-demineralisation using HRμCT. Seventy-two screw areas were randomised to either 2.5 mm or 1.5 mm pilot holes and to either be normal or reduced density. Maximum axial pull-out strength was measured.FindingsDemineralisation reduced bone density by 12% (p < 0.0001) and 11% (p < 0.0001) for 2.5 mm and 1.5 mm pilot hole diameters respectively. Pull-out strength reduced by 50% (p = 0.0001) and 44% (p < 0.0001) following demineralisation for both 2.5 mm and 1.5 mm pilot hole diameters. Pull-out strength increased by 51% (p = 0.0008) when inserting screws into 1.5 mm pilot holes in low density bone, and by 28% (p = 0.027) in normal bone.InterpretationPorcine bone can be demineralised to model low density cancellous bone. This novel model showed that pullout force is significantly reduced in lower density screw holes, but that this reduction can be mitigated by reducing pilot hole diameter for cancellous screws. |
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