Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The Oxford Unicompartmental Knee Replacement (UKR) is a commonly performed procedure, with a good clinical outcome at 15 years, however, radiolucent lines are commonly found beneath the tibial tray. With the projected increase in knee arthroplasty, particularly in younger patients, implant longevity is of paramount importance. The aim of this thesis is to understand how fixation is achieved with the Oxford UKR and how it can be improved. A histological study demonstrated that in the presence of a radiolucent line the tibial bone-cement interface is made up of a combination of direct bony contact, fibrocartilage and fibrous tissue. The radiolucency is more marked when there is more soft tissue. However in all cases there is some direct bony contact. Cemented and cementless fixation was compared in a randomised controlled study using radiostereometric analysis and fluoroscopic imaging of the interfaces. In the first year the cementless tibial component subsided on average 0.28 mm and had an increased posterior slope of 0.40°, whereas the cemented component only subsided 0.09 mm, with a 0.10° increase in slope. In the second year both components had very little further subsidence (mean<0.05 mm) and no increase in posterior slope. In the second year a single cementless tibial component subsided greater than 0.15 mm, whereas four cemented components, all with radiolucencies, subsided more than 0.15 mm. At two years the cemented components had a significantly higher prevalence of radiolucency (62% v 29%), with 24% having a complete radiolucency, whereas no cementless components had a complete radiolucency. Two designs of lateral UKR were also compared. These had a flat tibial component that predominantly transmits compressive loading, and a domed component that also transmits shear. There was a lower prevalence of radiolucency in the domed tibia (13% v 60%), even though there was a similar amount of migration as the cemented medial tibial component. In conclusion radiolucent lines, both partial and complete, are common with cemented components, and may, in part, be a result of compressive loading. They are associated with good long-term results and direct bone cement contact indicating satisfactory fixation. However, they are also associated with increased migration and soft tissue at the interface suggesting that the fixation, although satisfactory, is suboptimal. The cementless components had no complete radiolucencies and low levels of migration in the second year. This suggests that bone ingrowth and secure fixation occurs reliably, and therefore that cementless fixation may be better than cemented for the Oxford UKR.

"The understanding of bone healing and principles of fracture fixation have improved greatly over the past fifty years. Plating systems are ideal for use in fracture fixation as they facilitate direct and indirect bone healing due to the stability they provide at the fracture site. Their main failure mode, however, is through fatigue from the consistent loading and unloading of the plated bone when healing. The goal of this study was to evaluate the mechanical properties of the most prominent veterinary plating systems representing a comminuted fracture when mated to a bone model. These assemblies were loaded to acute failure in four-point bending and cycled in torsion to mimic fatigue loading. Based on the analyzed test data we are able to make a number of conclusions. After performing four-point bending tests, the String Of Pearls (SOP) system sustained the highest bending mechanical properties with a bending stiffness of 80.4±12.5 N/mm, bending structural stiffness of 8.7±1.4 N-m2, and bending strength of 11.6±1.7 N-mm. The Advanced Locking Plate System #10 (ALPS10) sustained the lowest bending mechanical properties with a bending stiffness of 40.0±1.9 N/mm, bending structural stiffness of 4.3±0.2 N-m2, and bending strength of 5.1±1.2 N-mm. Analysis of the cyclic fatigue data allow us to conclude that the Dynamic Compression Plate (DCP) system is able to maintain the highest absolute torque value across 15,000 torsion cycles and Fixin the lowest. This translates to 5.4±0.7 N-m and 3.5±0.4 N-m, respectively, when analyzed with Dixon-Mood equations and 5.4±2.5±N-m and 3.5±1.3 N-m, respectively, when analyzed with probability plots. In addition, the ALPS10 system is able to maintain the highest percentage of its failure torque and SOP the lowest. This translates to 76.4±16.3% and 43.6±5.3%, respectively, when analyzed with Dixon-Mood equations, and 72.9±28.6% and 44.2±22.1% when analyzed with probability plots. To aid in proper fracture healing, plating systems offering reduced or no contact with bone when applied in addition to screw holes across the entire plate length are preferred. The results of this evaluation are a start to better understanding plating system mechanics, which to develop further, will require further fatigue life testing in both loading conditions."

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Typescript. Bibliography: leaves [137]-[157]

This work introduces a direct method called FIXATION for solving the general motion vision problem. This Fixation method results in a constraint equation between translational and rotational velocities that in combination with the Brightness-Change Constraint Equation (BCCE) solves the general motion vision problem, arbitrary motion with respect to an arbitrary rigid environment. Neither Correspondence nor Optical Flow has been used here. Recently Direct Motion Vision methods have used the BCCE for solving the motion vision problem of special motions or environments. In contrast to those solutions, the Fixation method does not put such severe restrictions on the motion or the environment.

The use of herbicides in cropping systems is routine in western Canada as is the practice of rotating crops between cereals, oilseeds and pulse crops. Often, herbicides that are appropriate one year in the crop rotation are not compatible with the following crop. Additionally, certain herbicides are designed to target certain enzyme pathways that can interfere with amino acid synthesis. These pathways also exist in the microbial community, including Rhizobium species. Rhizobia have a unique symbiotic relationship with legumes. In return for a carbon source, rhizobia not only fix atmospheric dinitrogen (N2) for the plant, but also can increase soil N reserves for the following year. With herbicides targeting amino acid synthesis in both plants and microbes, there is a possibility that N2 fixation may be inhibited by the application of certain herbicides.<p> This project was designed to examine possible negative effects of herbicide application on N2 fixation in field pea (Pisum sativum L.) and chickpea (Cicer arietinum L.). The study included field, growth chamber and laboratory experiments in which the effects of pre- and post-emergent herbicides, as well as herbicide residues in soil were examined.<p> In the field experiments, some early season measurements suggested that herbicide application had a negative impact on various growth and N2 fixation parameters. However, as the season progressed, plants recovered from early herbicide damage and N2 fixation ultimately was relatively unaffected. Growth chamber experiments similarly revealed that N2 fixation was largely unaffected by herbicide application when the application rates were relatively low (i.e., at rates intended to simulate partial herbicide breakdown, and thus lower than the recommended field rate). Although, N2 fixation was suppressed where high rates of herbicide (i.e., greater than recommended field rate) were applied, the efficiency of the rhizobia to fix N2, (i.e., the amount of N2 fixed per unit nodule mass), was unaffected. This along with a laboratory experiment which monitored growth of rhizobia in vitro, confirmed that rhizobia were not directly affected by the herbicides used in this study and that overall N2 fixation was not inhibited directly by the application of these herbicides. It was concluded that any negative impact on N2 fixation caused by herbicides used in this study, was related to the impact of the herbicide on crop growth, and was not due to any direct effects of the herbicide on the rhizobia.

High levels of soil nitrogen (N) can interfere with N2 fixation of lentil (Lens culinaris) and have variable effects on growth, yield and maturity of this indeterminate crop in Saskatchewan. In a series of field and greenhouse experiments during 2006 to 2008, response of the above-ground biomass (DW), plant N, N2 fixation, yield and days to maturity (DTM) of lentil to different N sources, time of N availability, and also to two no tillage (NT) durations were studied. First, eight cultivars of lentil were grown under three fertility treatments of granular rhizobium inoculant, 50 kg N fertilizer ha-1 and a non-treated control in three environment-years at Saskatoon and Indian Head, SK. The fertility treatments, plant N status and N2 fixation did not alter lentil DTM, but weather did. On average, lentil matured 101 and 84 days after seeding with sufficient rain and with drought, respectively. Growth and yield of the lentil were identical in the inoculant and the N fertilizer treatments. The N fertilizer treatment occasionally restricted N2 fixation, but N shortage was compensated via more N uptake from soil. The greatest N accumulation of lentil occurred during podding to maturity and benefitted pod N content. By maturity, pod, stem and leaf had 60, 24 and 14% of total dry matter and 78, 9 and 13% of total plant N, respectively. Leaf N concentration, which closely resembled soil and plant N status, was reasonably predicted by SPAD chlorophyll meter observations after pod set. Yield of five lentil cultivars was tested for the effects of 25-years (LN) versus 5-years (SN) of no tillage in the Black Soil Zone at Indian Head, SK in 2006, 2007 and 2008. In the same location, CDC Sedley was grown with four N fertilizer rates at the both LN and SN. Under terminal drought in 2006, average DW, N content and yield of the lentil cultivars in SN were greater than in LN, likely because of inhibited N2 fixation by the amplified soil N in the LN. In this year, 60 kg N fertilizer ha-1 reduced the yield difference of CDC Sedley in SN and LN. Lentil yield was identical or tended to be greater in LN than in SN with more rain in 2007 and 2008 that prolonged N mineralization and N uptake. In the greenhouse study, applying N fertilizer from flowering until podding and until maturity increased DW, N content and yield, and delayed maturity of lentil compared to lentil relying on N2 fixation. Later flowering of one cultivar or greater N2 fixation in one soil medium diminished the variation of inoculated lentil with the post-flowering N treatments, suggesting N fixation could supply lentil N requirement. Large-seeded cultivars produced greater yield than the small-seeded cultivars across environments in the fertility treatment study. Cultivar CDC Milestone produced comparable yield to high-yielding cultivars CDC Plato and CDC Greenland, but matured earlier. This cultivar showed promising results under both cool-wet and drought conditions. In contrast, CDC Sedley had lower on N2 fixation and HI values across the experiments. In the Black Soil Zone, CDC Milestone and CDC Robin performance was improved by improved HI and N2 fixation. Overall, results of this thesis do not support the application of N fertilizer for inducing early maturity in lentil. Soil inoculation with commercial strains is suggested for Saskatchewan cropping systems. Applying N fertilizer is not required, unless soil test results suggest otherwise. In places like Indian Head, SK, cultivars with greater N2 fixation and higher HI can better fit the short growing season, cool temperature and high soil N content.

High levels of soil nitrogen (N) can interfere with N2 fixation of lentil (Lens culinaris) and have variable effects on growth, yield and maturity of this indeterminate crop in Saskatchewan. In a series of field and greenhouse experiments during 2006 to 2008, response of the above-ground biomass (DW), plant N, N2 fixation, yield and days to maturity (DTM) of lentil to different N sources, time of N availability, and also to two no tillage (NT) durations were studied. First, eight cultivars of lentil were grown under three fertility treatments of granular rhizobium inoculant, 50 kg N fertilizer ha-1 and a non-treated control in three environment-years at Saskatoon and Indian Head, SK. The fertility treatments, plant N status and N2 fixation did not alter lentil DTM, but weather did. On average, lentil matured 101 and 84 days after seeding with sufficient rain and with drought, respectively. Growth and yield of the lentil were identical in the inoculant and the N fertilizer treatments. The N fertilizer treatment occasionally restricted N2 fixation, but N shortage was compensated via more N uptake from soil. The greatest N accumulation of lentil occurred during podding to maturity and benefitted pod N content. By maturity, pod, stem and leaf had 60, 24 and 14% of total dry matter and 78, 9 and 13% of total plant N, respectively. Leaf N concentration, which closely resembled soil and plant N status, was reasonably predicted by SPAD chlorophyll meter observations after pod set. Yield of five lentil cultivars was tested for the effects of 25-years (LN) versus 5-years (SN) of no tillage in the Black Soil Zone at Indian Head, SK in 2006, 2007 and 2008. In the same location, CDC Sedley was grown with four N fertilizer rates at the both LN and SN. Under terminal drought in 2006, average DW, N content and yield of the lentil cultivars in SN were greater than in LN, likely because of inhibited N2 fixation by the amplified soil N in the LN. In this year, 60 kg N fertilizer ha-1 reduced the yield difference of CDC Sedley in SN and LN. Lentil yield was identical or tended to be greater in LN than in SN with more rain in 2007 and 2008 that prolonged N mineralization and N uptake. In the greenhouse study, applying N fertilizer from flowering until podding and until maturity increased DW, N content and yield, and delayed maturity of lentil compared to lentil relying on N2 fixation. Later flowering of one cultivar or greater N2 fixation in one soil medium diminished the variation of inoculated lentil with the post-flowering N treatments, suggesting N fixation could supply lentil N requirement. Large-seeded cultivars produced greater yield than the small-seeded cultivars across environments in the fertility treatment study. Cultivar CDC Milestone produced comparable yield to high-yielding cultivars CDC Plato and CDC Greenland, but matured earlier. This cultivar showed promising results under both cool-wet and drought conditions. In contrast, CDC Sedley had lower on N2 fixation and HI values across the experiments. In the Black Soil Zone, CDC Milestone and CDC Robin performance was improved by improved HI and N2 fixation. Overall, results of this thesis do not support the application of N fertilizer for inducing early maturity in lentil. Soil inoculation with commercial strains is suggested for Saskatchewan cropping systems. Applying N fertilizer is not required, unless soil test results suggest otherwise. In places like Indian Head, SK, cultivars with greater N2 fixation and higher HI can better fit the short growing season, cool temperature and high soil N content.