The thickness of the cement mantle around the femoral component of total hip replacements is a contributing factor to aseptic loosening and revision. Nevertheless, various designs of stems and surgical tooling lead to cement mantles of differing thicknesses. This thesis is concerned with variability in cement thickness around the Stanmore Hip, due to surgical approach, broach size and stem orientation, and its effects on stress and cracking in the cement. The extent to which cement mantle thickness varies in clinical practice as a result of surgical approach was investigated, through retrospective radiographic analysis. The posterior approach was associated with a thicker and more uniform cement mantle. Stress distributions in the cement mantle around Stanmore hips and surrounding cortical bone were investigated using finite element analysis, under a simulated gait load. Thicker cement was found to produce lower maximum principal stress in the cement and to reduce the likelihood of bone resorption due to stress shielding. Bone density was found to strongly affect stress levels in the bone and cement, but not to alter this result. Stanmore Hips were implanted into synthetic femurs with different cement thicknesses and stem alignments. Crack measurement and analysis was conducted, following fatigue testing under a simulated stair-climbing load. Crack length was found to be independent of overall cement mantle thickness, suggesting that thinner mantles would fail sooner. However, crack length was highly sensitive to local cement thickness, with regions of 1 mm or less containing longer and more concentrated cracks. Stem alignment and cement mantle uniformity are thus more critical to cement damage than broach size. Finite element simulations incorporating creep and nonlinear damage accumulation were performed to investigate cracking in the cement mantles around Stanmore Hips with varied cement thickness, interfacial bonding and collar design. Simulations represented the simple stair-climbing joint contact load used in fatigue tests and a more realistic stair-climbing load incorporating muscle forces and physiological bone properties. In all cases, damage levels were much higher when the stem-cement interface was bonded. Cement mantle thickness was of limited importance to cement damage in debonded cases, in agreement with fatigue test results, but was critical in bonded and collarless cases. Damage around a smooth, debonded stem with a collar is thus much less sensitive to cement thickness than around rough/bonded or collarless stems.

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Propuisive force generated by swimmers' hand/forearm is the key factor determining performances in human competitive swimming. This work analysed the propulsion given by swimmer's arm performing front crawl stroke by using two complimentary methods: experimental tests and computational methods. The experimental part of the project aimed to derive both appropriate input and validation data from wind tunnel experiments on two models of human arm in order to obtain Drag and Lift values and related pressure distribution. However, due to the limitations in the experimental methods in terms of added terms, numerical approach becomes an invaluable tool in such simulations. The most prominent approach is the Computational Fluid Dynamics (CFD). The main results reported that the Drag was the one that contributes more for the proplllsioD An important and innovative element that has been analysed in this work is the special consideration to the dynamic of structures surrounded by water in term of induced acceleration and production of extra force on the structure in addition to the fluid-dynamic drag force. These results pointed out that the acceleration of hand/arm provides more propulsion to swimmers, confirming that some unsteady mechanism must be present in swimming propulsion. Another important aspect of this work has been focusing on the real swimmer stroke trajectory, as a three dimensional approach, by recording a competitive swimmer during training with three underwater cameras and by analysing the swimmer arm movement performing stroke. Drag and Lift forces have been calculated and the results obtained showed a lower profile for both forces, compared to those ones obtained in a configuration with straight or fixed elbow angle (20 analysis). This innovative and original approach to the study of swimming made these results more reliable for a complete, comprehensive and reliable analysis.

Hydroxyapatite (HA) is a bioactive calcium phosphate based ceramic commonly used. as a bone graft substitute. The bioactivity of this material has been reported to be enhanced through site specific substitution of 0.8wt% silicate for phosphate into the HA lattice (SiHA). The aim of this thesis was to explore the possible mechanisms behind this bioactivity enhancement. Two hypothesises were proposed whereby bioactivity may be enhanced by either (1) an 'indirect effect', where alterations in the ion concentrations in the fluid surrounding the graft materials influenced osteoblast development or metabolism and/or (2) by a 'direct effect', where differences in the material physiochemistry influenced protein adsorption, which in subsequently promotes osteoblast attachment and consequently development or metabolism. In order to probe these two hypotheses a broad area of activity was undertaken, including production of morphologically matched HA and. SiHA, analysis of surface physiochemistry and chemical interactions under cell culture conditions in addition to analysis of material-protein interactions, cell attachment, metabolism and development. . Whilst the morphological parameters of the microporous HA and SiHA were matched, differences in the physiochemical properties were noted, such' as the increase in surface free energy from 29.43±6.39mJ/m2 (HA) to 56.67±1.07mJ/m2 (SiHA). Exposure of HA and SiHA to cell culture . medium led to a depletion of 10.8% and 27.1 % phosphate ions in medium respectively. Moreover, exposure to SiHA resulted in a significant increase in pH and release of up to 0.22mM silicon in the medium. Serum proteins were identified to influence the ionic interactions between the apatite and medium. However, these significant changes in ion composition were not seen to impact on the development of osteoblast-like cells. Impro\red bioactivity through the 'indirect effect' of ionic interactions between SiHA and the surrounding medium was therefore not established. Analysis of serum protein adsorption demonstrated that within 24 hours, 50±5.2J.lg and 35.9±4.0J.lg total protein was adsorbed to SiHA and HA specimens respectively. Further to the determination of ...

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