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Technical Briefs

A New System to Improve Screw Fixation to Bones

[+] Author and Article Information
A. Yánez1

Department of Mechanical Engineering, Biomechanical Laboratory,  Las Palmas University, Engineering Departmental Building, Campus de Tafira Baja, 35017 Las Palmas de Gran Canaria, Spain e-mail: myanez@dim.ulpgc.esHospital Perpetuo Socorro and Department of Medical and Surgical Science,  Las Palmas de Gran Canaria University, c/León y Castillo 407, 35017 Las Palmas de Gran Canaria, SpainDepartment of Mechanical Engineering, Biomechanical Laboratory,  Las Palmas University, Engineering Departmental Building, Campus de Tafira Baja, 35017 Las Palmas de Gran Canaria, Spain

G. L. Garcés, J. A. Carta, A. Cuadrado

Department of Mechanical Engineering, Biomechanical Laboratory,  Las Palmas University, Engineering Departmental Building, Campus de Tafira Baja, 35017 Las Palmas de Gran Canaria, Spain e-mail: myanez@dim.ulpgc.esHospital Perpetuo Socorro and Department of Medical and Surgical Science,  Las Palmas de Gran Canaria University, c/León y Castillo 407, 35017 Las Palmas de Gran Canaria, SpainDepartment of Mechanical Engineering, Biomechanical Laboratory,  Las Palmas University, Engineering Departmental Building, Campus de Tafira Baja, 35017 Las Palmas de Gran Canaria, Spain

1

Corresponding author.

J. Med. Devices 5(4), 044501 (Nov 07, 2011) (5 pages) doi:10.1115/1.4005227 History: Received December 15, 2010; Revised September 10, 2011; Published November 07, 2011; Online November 07, 2011

Plates and non-locked screws used in the treatment of osteoporotic bone fractures frequently become loose due to everyday mechanical demands. Currently, locking plates and screws are the gold standard treatment for these fractures. However, their use has several limitations and complications as they are technically demanding, and their cost is very expensive. To improve the fixation strength of traditional unlocked plate and screw constructs, we have developed a new fixation system based on a very old concept. The system consists of a screw locking element (SLE) manufactured from PEEK, which is attached to the end of the screw shaft once it has traversed both bone cortices. A specially designed tool is used to facilitate its attachment to the screw. This tool makes it possible for the screw to traverse an osteosynthesis plate or lockwasher as well as both bone cortices and to easily find the SLE, fixing it against the far cortex. We tested the pull-out strength of SLEs and compared the results with previously published data for human femoral cortex pull-out strength. Our laboratory tests demonstrate that the mean SLE pull-out strength was 3864 ± 47.61 N, while that observed for a human femoral diaphysis cortex was 4071.54 ± 1461.69 N. This difference was not significant (p > 0.05). This new system can easily be used with any type of osteosynthesis in osteoporotic or osteopenic bones, with the screws being placed on weakened areas of the bone (e.g., fissure lines, previous orifices, or thinned metaphyseal bone cortex), or to replace over-torqued screws. It is particularly suitable for veterinary trauma, where immediate weight-bearing protection after fracture treatment is nearly impossible.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Scheme of a screw locking element and the device used for its insertion. H = handles, M = male part, F = female part, P = pivoting jaw, G = interchangeable drill guide, O = drill guide receptor, and S = clamp bolt.

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Figure 2

Outline of the working procedure. (a) Fixing device, including an SLE to be inserted on the far cortical. (b) The correct position is maintained by the clamp bolt (S). (c) Drill bit passing through the appropriate guide. (d) Screw insertion. (e) Withdrawing of the fixing device. (f) Screw locked by the SLE.

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Figure 3

Pull-out strength test of a screw-SLE model

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Figure 4

Pull-out test of a screw-bone surrogate-SLE system

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Figure 5

Load-displacement curve from one of the 10 specimens of isolated SLEs

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Figure 6

Load-displacement curves from specimens of screw-bone surrogate and screw-bone surrogate-SLE

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