Background: Total knee arthroplasty (TKA) is a well-established surgical operation. Some epidemiology studies showed that TKA operations continue to improve in developed and developing countries. However, among these operations, the satisfaction rating of TKA outcomes was much lower than those of total hip arthroplasty (THA) (75% vs. 97%). / The knee joint is kinematically more complex than the hip joint because of its wider range of movement, including sliding and rotation during flexion, which make it difficult to restore function. Many investigations demonstrated that malalignment and unbalanced soft tissue tension are two major factors that influence the functional restoration of knee joints after TKA. Restoration of the lower limb mechanical axis is now easier to achieve owing to the development of the computer navigation system. However, balancing soft tissue tension still remains a problem, making it a subject of great interest in research. / A group of researchers pointed out that the conventional TKA method focuses too much on the restoration of the mechanical axis but neglects its anatomic and kinematic considerations. This notion led to their proposal of another method, namely, kinematical alignment, which is not perpendicular to the mechanical axis but parallel to the posterior condylar axis. Some clinical studies showed that the short-term and mid-term outcomes of kinematically aligned TKA knees achieved pain relief and functional restoration better. However, the underlying mechanisms have not been studied. / The current study aims to investigate the underlying mechanisms of the kinematical alignment method in four aspects: anatomy, kinematics, biomechanics, and bone preservation. We hypothesize the following. 1. The posterior condylar axis is more reliable than the epicondylar axis as a reference for TKA operations and anthropometrical studies of the knee joint. 2. The kinematical alignment method preserves the bone cutting volume better than the mechanical alignment method. 3. Varus deformation influences the kinematics and biomechanics in the tibiofemoral joint of the normal knee during static standing and flexion. 4. Kinematical alignment is better than the mechanical alignment in restoring normal kinematics and biomechanics for TKA knees during flexion. 5. Kinematical alignment may increase stress at the medial side of the tibiofemoral joint of TKA knees at static standing posture. / Methods: 1. In this study, a clearer and easily reproducible marking area on the posterior femur condyle surface was defined, from which an axis was obtained, namely, the newly defined posterior condylar axis (NPCA). Based on the NPCA, a coordinate system of the knee joint was established. Anthropometrical study of the NPCA and the clinical epicondylar axis (CEPA) were carried out on 52 normal Chinese subjects (50–80 years old, female: male = 1:1). 2. A weight-bearing magnetic resonance imaging (MRI) experiment was further designed and carried out on the normal subjects and the knee osteoarthritis (OA) patients. Eight MRI scans were performed at flexion angles of 0°, 20°, 40°, and 60° with and without placing an 18 kg weight on each volunteer. After scanning, the three-dimensional geometries of the knee bones were reconstructed, and abduction angles of the normal and varus knees were measured and compared. 3. Simulations of bone osteotomy according to mechanical alignment and kinematical alignment methods were performed on 12 varus OA knees. Bone volumes of the distal femur cut, proximal tibial cut, anterior and posterior femur cut, and anterior and posterior chamfer cut of the two alignment methods were measured and compared. 4. From the MRI image of a young healthy volunteer, a finite element model of the normal knee with a varus angle of 0° was constructed. Based on this initial construction, another 5° deformed varus knee model was also constructed. Varus deformation simulation was perform on the normal knee. Static standing simulation and flexion simulation were applied on both normal and varus knee models. 5. Two finite element models of the mechanically and kinematically aligned TKA knees were constructed based on the normal knee model. Static standing simulation and flexion were also applied on the two TKA knee models. / Results: The anthropometrical study showed that the angle between the NPCA and CEPA was about 3.5° on the coronal plane and 1.2° on the axial plane regardless of alignments. Moreover, the CEPA was nearly perpendicular to the lower limb mechanical axis in all alignment groups, whereas the NPCA was more orthogonal to the femoral mechanical axis in the varus group. The NPCA was also almost parallel to both inferior and posterior condylar lines in all alignment groups, whereas the CEPA was only parallel to the posterior condylar line. / The weight-bearing MRI experiment showed that as the knee flexed from 0° to 60°, the abduction angles of normal knees increased from -1° to 2°, whereas those of varus knees decreased from 4° to 3°. Significant differences in abduction angles were found between normal and varus knees at flexion angles of 0°, 20° and 40° with or without weights. No significant difference was found between weight-bearing and non-weight-bearing conditions in both normal and varus knees. / The bone osteotomy simulation showed that the kinematical alignment method saved 49.1±6.0% of bone volume in the distal femur cut, 26.3±10.4% in the posterior femur cut, 35.6±5.4% in the tibial plateau cut, and 28.4±4.4% in total. / The varus deformation simulation showed that as the knee varus angle increased from 0° to 5°, the peak stress linearly increased at a rate of 0.8 MPa per varus angle in the medial tibial cartilage, but decreased at a rate of 0.2 MPa per varus angle in the lateral tibial cartilage. Moreover, stress was almost equally distributed in the medial and lateral tibial cartilages of the normal knee at static standing posture, whereas stress localized in the medial tibial cartilage of the varus knee. / Flexion simulation of the normal and varus knees showed that peak stress in the medial tibial cartilage of the varus knee decreased sharply from 2.18 MPa to 0.87 MPa as the knee flexed from 0° to 20°. Peak stress in the medial and lateral tibial cartilages of the normal knee was also almost equal at all flexion angles, whereas similar peak stress was observed in the varus knee only after a flexion angle of 20°. / Static standing simulation of both TKA knees showed that lateral tibial peak stress in the mechanically aligned TKA knee was approximately 0.2–0.8 MPa higher than that in the kinematically aligned TKA knee. Meanwhile, the medial tibial peak stress in the kinematically aligned TKA knee was approximately 0.5–1.2 MPa higher than that in the mechanically aligned TKA knee. / Flexion simulation of post-operative knees showed that stress was nearly equally distributed in the medial and lateral tibial inserts of the kinematically aligned TKA knee as the knee flexed from 0° to 50°. Moreover, axial rotation angles in the kinematically aligned TKA knee were approximately equal to those in the normal knee during flexion, whereas in the mechanically aligned TKA knee, the femur condyle was axially rotated in the opposite direction. Load partially transferred through the medium spine after a flexion angle of 40°, and peak stress in the medium spine was at least four times higher than those in the concaves of the insert component. / Conclusion: NPCA is more reliable than CEPA as a reference to determine the axial and rotational alignments of the femoral condyle for TKA surgeries and anthropometrical studies of the knee. Kinematical alignment is also better than the mechanical alignment in preserving the bone cutting volume by nearly 30%. / Varus deformation significantly shifts the stress to the medial side of the knee in a static standing posture, but its effect is reduced during flexion. It indicates that the inferior side of medial femoral condyle would be more likely to suffer knee OA rather its posterior side from the biomechanical view. / Kinematical alignment increases stress at the medial tibiofemoral joint of the TKA knee in a static standing posture, which may influence its long-term condition. However, kinematical alignment is better than mechanical alignment in restoring normal kinematics and biomechanics for TKA knees during flexion. Peak tibiofemoral contact force in the normal and TKA knees can reach four to six times the body weight in a squatting position. Thus, restoring normal kinematics and biomechanics during flexion is important. / 背景：全膝关节置换术（TKA）已成为一种常规手术。一些流行病学研究显示TKA在发达国家和发展中国家都呈持续增长趋势；然而与全髋关节置换术（THA）相比，TKA的满意度要明显低于THA（75% vs 97%）。 / 从运动学角度观察，膝关节运动学结构要比髋关节复杂：在膝关节弯曲过程中，其内既有滑动又有轴向转动，以至于很难恢复其功能。许多研究人员证明下肢力线错位和膝关节内部软组织不平衡是影响TKA术后其功能恢复的两个主要原因。得益于计算机辅助导航系统的发展，正常下肢力线已经能够较容易实现恢复；但是如何做好膝关节软组织平衡还是一个悬而未决的问题，目前许多相关研究正在进行当中。 / 最近有一组研究人员指出传统的TKA手术方法太过于关注恢复下肢力线，而忽略了其解剖和运动学方面的因素，而这对实现软组织平衡至关重要。基于上述原因，他们提出了一种新的截骨方法——运动学对线。基于这种截骨方法，其股骨远端截骨面不再垂直于下肢力线，而是平行于股骨后髁轴线。一些临床研究结果已经表明运动学对线的TKA术后的短期疼痛舒缓和中期功能恢复效果都要优于力学对线的TKA；然而其内在机理尚未被研究。 / 本次课题拟从四个方面去研究运动学对线的截骨方法的内在机理：解剖学、运动学、生物力学和节约骨量。我们假设： 1. 股骨后髁轴线比股骨髁间轴线更加稳定，更适合作为膝关节置换术和膝关节形态测量的参考轴线； 2. 相比力学对线的方法，运动学对线的方法能够有效减少截骨量； 3. 膝关节畸形内翻会改变其胫股关节在站立位和弯曲过程中的运动学和生物力学特性； 4. 运动学对线的方法可能会增加TKA术后的胫股关节在站立位时的内侧应力； 5. 运动学对线的方法比力学对线的方法更能有效的恢复TKA术后膝关节在弯曲过程中的正常运动学和生物力学特性。 / 方法： 1. 本次研究提出一种更加清晰的、易重复的股骨后髁接触表面的边界定义方法；基于这个表面拟合出一个圆柱，其轴线即为——新股骨后髁轴线（NPCA）。基于NPCA建立了膝关节的坐标系统，且设计了一套人体形态学测量方法测量了52位中国人的股骨NPCA和髁间轴线（CEPA）（年龄：50~80；男：女=1:1）。 2. 设计了一组负重核磁共振（MRI）试验去测量健康和膝关节炎（OA）患者的胫股关节运动学特性。基于特殊设计的试验工具，每一位志愿者都进行了0°、20°、40°和60°膝关节弯曲角度下的，以及负重与非负重状态下的共8组MRI扫描。扫描完成后，膝关节骨性结构的三维几何模型被重建出来，其正常与内翻膝关节的外展角度也被测量出来并进行比较。 3. 对12只内翻膝关节分别进行了力学对线和运动学对线的两种不同截骨方法的截骨模拟。两种截骨方法下的股骨远端截骨、胫骨近端截骨、股骨前髁与后髁截骨、以及股骨前髁与后髁倒角截骨的骨量都被分别计算出且进行比较。 4. 基于一位年轻健康志愿者的MRI图像建立了0°内翻的正常膝关节的有限元模型，且在其基础上另建立5°内翻的膝关节模型。之后，对正常膝关节模型进行了内翻模拟分析；且对正常和内翻膝关节模型都分别进行了站立位和弯曲运动的模拟分析。 5. 基于正常膝关节模型建立了力学对线和运动学对线的两种TKA膝关节模型。之后，对两种TKA膝关节模型都分别进行了站立位和弯曲运动的模拟分析。 / 结果：人体形态学测量结果显示正常、内翻和外翻膝关节的NPCA与CEPA之间的夹角在冠状面都约为3.5°，在横断面都约为1.2°。此外，三组膝关节的CEPA都几乎与下肢力线垂直；而内翻组的NPCA比其CEPA更加垂直于其股骨力线。再者，所有膝关节组的NPCA都几乎同时平行于股骨下髁和后髁切线，而其CEPA却只平行于股骨后髁切线。 / 负重MRI实验结果显示在膝关节0°至60°弯曲过程中，正常膝关节的外展角从-1°增至2°；而内翻膝关节外展角从4°减至3°。正常与内翻膝关节在0°、20°和40°弯曲角度时的外展角表现出显著差异；然而正常与内翻膝关节在负重与非负重情况下的外展角都无显著差异。 / 截骨模拟结果显示运动学对线的截骨方法节约了49.1±6.0%的股骨远端截骨骨量、26.3±10.4%股骨后髁截骨骨量、35.6±5.4%胫骨近端截骨骨量，总计节约28.4±4.4%的截骨骨量。 / 内翻模拟分析结果显示在正常膝关节从0°內翻至5°过程中，其内侧胫骨软骨中的最大应力以0.8MPa每内翻角的速率线性递增；而其外侧胫骨软骨中的最大应力却以0.2MPa每内翻角的速率线性递减。此外，站立位时正常膝关节的内外侧胫骨软骨中的应力呈均匀分布；而内翻膝关节中的应力则高度集中在内侧胫骨软骨中。 / 正常和内翻膝关节的弯曲模拟分析结果显示内翻关节在从0°弯曲至20°过程中，其内侧胫骨软骨中的最大应力从2.18MPa急剧减少至0.87MPa。此外，在所有弯曲角度下，正常膝关节内、外侧胫骨软骨中的最大应力值相近；而在内翻关节中类似情况仅在20°弯曲角度后出现。 / 两种TKA膝关节模型的站立位模拟分析结果显示：力学对线的TKA膝关节的外侧胫骨衬垫最大应力比运动学对线的TKA膝关节的外侧胫骨衬垫的最大应力要高0.2至0.8MPa；而运动学对线的TKA膝关节的内侧胫骨衬垫最大应力比力学对线的TKA膝关节的内侧胫骨衬垫的最大应力要高0.5至1.2MPa。 / 两种TKA膝关节模型的弯曲模拟分析结果显示：在膝关节从0°弯曲至50°过程中，运动学对线的TKA膝关节胫骨衬垫内外侧的应力近于平均分布。此外，运动学对线的TKA膝关节在所有弯曲角度下的轴向旋转角度都与正常膝关节的近乎一致；而力学对线的TKA膝关节的轴向旋转角度却与其方向正好相反。在40°弯曲角度以后，部分应力将通过衬垫中部突柱传递；且中部突柱内的最大应力要高出衬垫凹窝内的最大应力至少四倍。 / 结论：NPCA是比CEPA更为稳定的能判定股骨髁轴向和弯曲旋转对齐状态的参考轴线，可更好的辅助TKA手术和膝关节形态学测量研究。此外，与力学对线的截骨方法相比，运动学对线的截骨方法能节约将近30%的截骨骨量。 / 内翻畸形形变会显著增大膝关节在站立位时的内侧应力，但这一影响会在弯曲过程中削弱。这一结果表明从力学角度观察股骨下髁比股骨后髁更容易患骨性关节炎及更容易产生形变。 / 运动学对线的方法增加了其TKA膝关节在站立位时内侧应力，这可能会影响其关节假体的远期使用寿命；然而在弯曲运动过程中，运动学对线的方法比力学对线的方法能更好的恢复其TKA膝关节的正常运动学和生物力学特性。由于在下蹲过程中，正常与TKA膝关节中胫骨关节内最大接触压力可达人体体重的4至6倍；因而恢复弯曲过程中的正常运动学与生物力学特性显得更为重要。 / Shi, Dufang. / Thesis Ph.D. Chinese University of Hong Kong 2015. / Includes bibliographical references (leaves 281-289). / Abstracts also in Chinese. / Title from PDF title page (viewed on 14, September, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 80-82).

Concrete is probably the most widely used construction material in the world. In the Arabian Gulf region, deterioration of concrete due to the aggressive environment is recognized to be the main factor affecting their structural integrity. The durability of concrete structures can be preserved by various protection methods; however, using cement replacement materials is one of the most effective and economic methods of maintaining their stability as well as extending their service life. The aim of this project is to study four interrelated aspects, namely, (1) the effect of hot environment on the properties of fresh concrete incorporating mineral admixtures, (2), the influence of exposure environment on the engineering properties of hardened concrete, under various curing conditions, without and with mineral admixture, (3), the differences in porosity and pore structure of the same set of mixes, and, (4) the effect of outdoor exposure on the durability-related properties of concrete. To achieve the above aims, the experimental programme involved the study of five different mixes of combinations of silica fume/slag and silica fume. The effects of real exposure to the Arabian Gulf environment of these mixes subjected to four curing regimes, namely, continuous water curing, no water curing after demolding, and air drying after 3 and 7 days of initial water curing were investigated. The properties investigated include (1) consistency and setting times of cement pastes, workability and workability loss with time, (2) engineering properties such as compressive strength, dynamic modulus of elasticity, pulse velocity, shrinkage, expansion and thermal expansion, (3) microstructural properties such as porosity and pore size distribution, (4) durability-related properties such as permeability, water absorption and carbonation depth. The results show that exposure to hot environment results in rapid setting times, faster loss of slump, higher porosity, coarser pore structure and more permeable concretes. It was found that part cement replacement by silica fume and slag improves the quality of concrete mixtures, refined the pore structure and produced concretes with very low porosity and continuous pore diameter in both indoor and outdoor environment. The properties of concrete containing mineral admixture appear to be more sensitive to poor curing than the plain concrete, with the sensitivity increasing with increasing amount of slag in the mixture.

Unemployment and the duration of stay in this labour market state have motivated many empirical studies in the last three decades. The main focus of the empirics, up until recently, has been to model the total duration of unemployment, defined by the termination of a job and the commencement of a new labour market state. This new labour market state is most often defined by the start of a new job. However, many labour markets function within a system of wage replacement benefits for unemployed workers via state-run Unemployment Insurance (UI) programmes. More recent studies have focused on the period of insured unemployment in relation to specific programme rules such as wage replacement level (the benefit level) and maximum weeks of benefit entitlement. This thesis takes advantage of rule changes to the benefit level and maximum entitlement within the Canadian UI programme in the early 1990s to examine their impact on UI durations. A random sample of UI claims filed by male claimants from thirteen geographic regions within the four provinces of Atlantic Canada was selected. Unemployment Insurance durations are defined both by the last week of UI benefit receipt and the first week of active labour market activity while on claim. The analysis uses non-parametric, semi-parametric and parametric estimation techniques in obtaining covariate and baseline hazard influences on the duration of UI claims. The estimation results indicate that there are statistically significant benefit and entitlement effects as well as UI duration differences by region, occupation and industry. Unique UI durations were also revealed for exit events defined by the start of part-time earnings, full-time earnings and the start date of training while on a UI claim. Overall, programme changes which have reduced programme generosity have shortened UI durations primarily by reducing the maximum number of weeks ofUI entitlement

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