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dc.contributor.advisorPankaj, Pankajen
dc.contributor.advisorSimpson, Hamishen
dc.contributor.authorMacLeod, Alisdair Rodericken
dc.date.accessioned2017-04-26T09:33:04Z
dc.date.available2017-04-26T09:33:04Z
dc.date.issued2015-06-29
dc.identifier.urihttp://hdl.handle.net/1842/21693
dc.description.abstractA large number of bone fractures are treated with stabilisation devices that utilise metal wires or screws, which traverse the bone and are connected to an external frame or internal plate. Clinically, fixation devices are required to be able to: sustain loads; minimise patient discomfort and possible implant loosening; and promote healing. In the recent years locking plates have become increasingly popular for osteoporotic or complex fractures, which can be difficult to manage. It, however, remains unclear as to how these devices need to be configured for optimum clinical performance. This thesis investigates the mechanics of locking plates, factors that influence their performance and provides guidance to optimise the placement of screws. Finite element simulation and analytical models were developed and validated using lab-based experimental models. The local behaviour around the screw-bone interface is considered and the implications of different modelling assumptions assessed. A novel method of simulating the effect of radial interference due to pilot-hole size is proposed. Different screw types are evaluated: osteoporotic bone is found to be particularly susceptible to the screw tightening preload used in compression screws; far-cortical locking screws are found to slightly reduce device stiffness but substantially increase strain levels around screw holes. Finite element simulations show that many of the local effects, such as preloads and contact modelling, can profoundly influence the prediction of strains around screws but do not generally influence the global load-displacement behaviour; the screw-plate connection and bone/plate material and geometric properties are found to have an influence on global stiffness predictions. The key determinants of load-displacement behaviour evaluated through models are the loading and restraint conditions, which explain the huge range of stiffness predictions in the literature (three orders of magnitude). An analytical model based on 7 bone-plate construct parameters is developed. Despite its simplicity, the model is found to be able to predict the axial stiffness for experimental tests conducted and for 16 other cases from five previous studies with an average error of 20%. The manner of load application, not considered in the literature, is shown to dramatically alter predictions of plate stress, strains within the bone and conclusions regarding screw placement. Even with the inclusion of muscles forces, the choice of restraint condition dominates the mechanical behaviour. Using the models, the influence of screw position is systematically evaluated in varying bone qualities under axial loading and torsion and guidance for optimising fixation is developed.en
dc.contributor.sponsorotheren
dc.language.isoen
dc.publisherThe University of Edinburghen
dc.relation.hasversionAlisdair R. MacLeod, Pankaj Pankaj, A. Hamish R.W. Simpson, The reasons conventional screws are inferior to locking screws in osteoporotic bone: a finite element explanation, Computer methods and in Biomechanics and Biomedical Engineering, 2014; 18(16):1818-25. DOI: 10.1080/10255842.2014.974580.en
dc.relation.hasversionAlisdair R. MacLeod, Pankaj Pankaj, A. Hamish R.W. Simpson, Does screw-bone interface modelling matter in finite element analyses?, Journal of Biomechanics 2012; 45(9):1712-6. http://dx.doi.org/10.1016/j.jbiomech.2012.04.008en
dc.relation.hasversionMacLeod A, Pankaj P, 2014, Computer simulation of fracture fixation using-extramedullary devices: an appraisal. In Computational Biomechanics in Medicine, Springer, 87-99.en
dc.relation.hasversionMacLeod, A., Pankaj, P., and Simpson, H., 2012, The Effect of Varying Screw Configuration of the Mechanical Response of Locking Plate Fixators. Journal of Biomechanics, 45, Supplement 1(0), S218. http://dx.doi.org/10.1016/S0021- 9290(12)70219-1en
dc.relation.hasversionMacLeod, A., Pankaj, P., and Simpson, H., 2012, Screw-Bone Interface Modelling in Locking Plate FE Models. Journal of Biomechanics, 45, Supplement 1(0), S333. http://dx.doi.org/10.1016/S0021-9290(12)70334-2en
dc.relation.hasversionMacLeod, Alisdair; Pankaj, Pankaj; Simpson, Hamish, A. Finite Element Comparison of Locking Plate and Compression Plate Fracture Fixation, The Proceedings of the 10th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering, 357-362, Berlin, 2012.en
dc.relation.hasversionAlisdair R. MacLeod, Pankaj Pankaj, A. Hamish R.W. Simpson, The Importance of Modelling Bone-Implant Interface in Locking Plate FE Models, Journal of Bone Joint Surgery (British) 2012 vol. 94-B no. SUPP XXXVI 84.en
dc.subjectlockingen
dc.subjectplatesen
dc.subjectscrewen
dc.subjectboneen
dc.subjectfractureen
dc.subjectstrainen
dc.subjectstressen
dc.titleModelling and optimising the mechanical behaviour of fractures treated with locking platesen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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