Objective- To compare the biomechanical properties of 3.5 locking compression plate (LCP) fixation to 3.5 limited contact dynamic compression plate (LC-DCP) fixation in a canine cadaveric, distal humeral metaphyseal gap model in static axial compression and cyclic axial compression and torsion. Study Design- Biomechanical in vitro study. Sample Population- 30 paired humeri from adult, medium to large breed dogs. Methods- Testing was performed monotonically to failure in axial compression on ten pairs of humeri, cyclically in axial compression for 10,000 cycles on ten pairs and cyclically in torsion for 500 cycles on the last ten pairs. Results- Humeral constructs stabilized with LCPs were significantly stiffer than those plated with LC-DCPs when loaded in axial compression (P=0.0004). When cyclically loaded in axial compression over 10,000 cycles, the LC-DCP constructs were significantly stiffer than those constructs stabilized with LCPs (P=0.0029). Constructs plated with LC-DCPs were significantly more resistant to torsion over 500 cycles than those plated with LCPs (P<0.0001), though no difference was detected during the first 280 cycles. Conclusions- The increased stiffness of LCP constructs in monotonic loading compared to constructs stabilized with non-locking plates may be attributed to the stability afforded by the plate-screw interface of locking plates. The LCP constructs demonstrated less stiffness in dynamic testing in this model, likely due to plate-bone offset secondary to non-anatomic contouring and occasional incomplete seating of the locking screws when using the torque-limiting screw driver. Clinical Relevance- LCPs yield less stiff fixation under dynamic loading than conventional LC-DCPs when applied to severely comminuted, metaphyseal fractures. Improving anatomical contouring of the plate and insuring complete screw insertion into the locking plate hole may improve stiffness when using LCPs in comminuted fractures. / Master of Science

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En soudage en phase solide, si la température peut avoir un rôle favorable, une sollicitation mécanique est également nécessaire pour s’affranchir de la couche d’oxyde recouvrant naturellement l’aluminium. Dans ce travail, on a ainsi cherché à comprendre l’importance de la sollicitation mécanique vis-à-vis de la création des jonctions métalliques. Dans ce but, 2 essais de soudabilité à froid ont été mis en place. L’essai de compression plane (CP) a pour but d’augmenter la surface à l’interface de soudage, de sorte à morceler la couche d’oxyde. Grâce à la microscopie, à une analyse par EF et à un modèle tensoriel de caractérisation de l’évolution des surfaces, les essais ont montré que, plus que l’importante déformation globale, le soudage se produit dans les zones de cisaillement maximum.Par conséquent, le second essai repose sur le cisaillement de l’interface de soudage : un tube sectionné est soumis à un effort de compression et de torsion alternée. Comme pour l’essai de CP, l’influence de divers paramètres a été étudiée. Parmi ceux-ci, l’état de surface (rugosités et propreté), l’angle de torsion (faible amplitude) et le nombre de cycles ont un rôle prépondérant. Les assemblages soudés ont ensuite été caractérisés mécaniquement et observés en microscopie (MEB-FEG, EBSD). Par rapport à l’essai de CP, on a pu constater une meilleure quantité et qualité des jonctions en compression-torsion alternée. De plus, un modèle thermodynamique a permis de conclure que les énergies mises en jeu sont trop faibles pour permettre un échauffement significatif : le soudage, sur environ 50% de l’interface en l’état actuel des choses, n’est réalisé que par des effets mécaniques locaux. / In solid-state welding, if the temperature generally has an important role (diffusion, recrystallization, etc.), a mechanical load is also necessary to override the oxide layer which naturally covers aluminium alloys. This work aims to understand the influence of the mechanical load on the formation of metallic bonds. To this end two cold weldability tests have been introduced. Firstly the plane strain channel-die compression of two cuboids sample aims to increase the surface at the welding interface in order to break up the oxide layer. Thanks to microscopy, a FEA model and a tensorial model of surfaces evolution, those results showed that, more than the important global deformation, welds were created in areas with maximum shear. Subsequently the second test aims to shear the welding interface: a tube is cut through its section and undergoes both a compression and a cyclic torsion load. As for our first weldability test, the influence of some parameters has been studied. Among them, the surface condition (roughness and cleanliness), the torsion angle (low amplitude) and the number of cycles are the most influential. Then the welded joints have been mechanically tested and microscopically observed (FEG-SEM and EBSD). In comparison with our first test, a higher quality and quantity of the joining has been showed. Moreover, a thermodynamic model concludes that the energies involved in this experimental process are too low to imply any local heating: the joining, on 50% of the welding interface as things stand, is only achieved thanks local mechanical effects.