Mechanical Engineering - Theses
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ItemHealthy patellofemoral kinematics and contact forces during functional activities( 2020)A better understanding of normal knee function is critical to the treatment of knee disorders. Limited data are available on knee biomechanics during functional activities such as walking, particularly in relation to the articulation of the patella. Three aims were formulated to address this gap in knowledge: 1) analyse the kinematics of the patellofemoral joint during functional activities, 2) determine the region of cartilage contact in the patellofemoral and tibiofemoral joints and their relationship to cartilage thickness, and 3) calculate the distribution of medial-lateral contact loads in the patellofemoral and tibiofemoral joints during level walking. These aims were achieved by first accurately measuring three-dimensional kinematics of the patellofemoral joint as healthy young people performed six activities: level walking, downhill walking, stair descent, stair ascent, open-chain knee flexion, and standing. These data were examined for notable kinematic characteristics of the patella during ambulatory activities and to determine how the motion of the patella and the tibiofemoral flexion angle are linked (i.e., coupled) together. Cartilage models were created of each participant’s knee in order to determine the region of cartilage contact for each of the activities performed, and to identify correlations between cartilage contact and cartilage thickness. Finally, musculoskeletal models with full six degree of freedom patellofemoral and tibiofemoral joints were created, used to calculate the medial-lateral contact loads at the knee during level walking, and finally validated against the measured kinematic data. These procedures have revealed important findings. Patellar flexion and anterior translation were coupled and linearly related to the tibiofemoral flexion angle. Medial shift and superior translation were likewise coupled to tibiofemoral flexion, and both displayed notable characteristics for all ambulatory activities: the patella shifted laterally at low tibiofemoral flexion angles and underwent rapid superior translation just prior to heel strike. Based on the activities tested here, the patellofemoral joint can effectively be modelled as a one degree of freedom joint. The centroid of cartilage contact for both joints appears to be determined by the tibiofemoral flexion angle, and hence geometry, rather than activity. Patellofemoral contact was concentrated on the lateral side of both the patella and the femur. In each pair of contacting regions within the knee, one side of the pair exhibited a positive relationship between cartilage thickness and contact (i.e., the medial and lateral tibial plateaus and the patella), while the other exhibited a weak or non-existent relationship (i.e., the medial and lateral femoral condyles in the tibiofemoral joint and the femur in the patellofemoral joint). The patellofemoral joint displayed two peaks in the contact force during level walking, one in early stance and one in swing phase, both at approximately 0.55-times bodyweight. Most of the patellofemoral contact force was transmitted through the lateral facet of the patella. The posterior component of hamstring muscle force contributed to the load transmitted to the patellar facets. These findings may assist with the diagnosis and treatment of many common knee disorders and will provide a useful source of information for future investigations into the knee.
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ItemIn vitro measurement and computational modelling of knee-joint contact mechanics during simulated load-bearing activity( 2016)The knee is one of the most complex joints in the human body. Knee joint disorders, such as osteoarthritis (OA), undermine the mobility and quality of life of those affected. Abnormal joint loading is widely acknowledged to be one of the primary causes of the onset and progression of knee OA. Yet, knee joint contact mechanics is still not well understood. This lack of understanding is partially due to the practical and ethical challenges involved in obtaining in vivo contact stress measurements at the patient-specific level. As a result of these difficulties, computational finite element (FE) modelling has emerged as a non-invasive alternative for research into knee joint contact mechanics. The present dissertation aimed to improve the current state of art of knee joint FE modelling and to enhance the techniques used to validate model contact predictions. An apparatus was designed and built to enable physiological dynamic loading simulations on cadaveric knee joints whilst bony kinematics and joint contact distributions were measured using a bi-plane fluoroscopy system and a real-time pressure measurement system, respectively. A subject-specific knee joint FE modelling framework incorporating a hyperelastic constitutive cartilage material model was developed, and the contact predictions of the tibiofemoral and patellofemoral joints were individually validated against in vitro experimental data. Contact mechanics of the tibiofemoral and patellofemoral joints were analysed during a simulated stair descent activity and a knee flexion task under quadriceps load, respectively. Sensitivity analyses were performed to identify the model parameters that had the greatest influence on the accuracy of model-predicted joint contact mechanics. The FE models closely reproduced the contact pressure patterns of both joints observed in the experimental measurements. Specifically, the shape and location of the contact region were qualitatively similar between the FE results and experimental data throughout the trial cycles, and the high contact pressure sub-regions were also successfully predicted. The FE model predictions of peak contact pressure, contact area, contact force and centre of pressure (COP) matched reasonably well with the experimental data for both joints. The root mean square errors (RMSE) were on the order of 15% (as a percentage of the corresponding peak experimental values). The average distance between the COPs of the model and experimental results was around 2.5 mm. The element-wise contact pressure comparison showed a typical error of about 25%. Strong correlations existed between the predicted and measured contact variables over time, with Pearson correlation coefficients typically larger than 0.8. The patellofemoral joint contact force was higher on the lateral facet in both the experimental and the FE results, consistent with previous findings by other studies. The results showed that changes in the stiffness of cartilage and meniscus, contact friction coefficients and model geometries consistently affected the predictions of the contact variables in both joints. Furthermore, inaccurate model geometries decreased the correlations between the experimental and calculated results. In general, the peak contact pressure was more sensitive to changes in model inputs compared to contact force and contact area. This finding demonstrates that peak contact pressure predictions require more accurate model inputs, in particular, the material properties and geometries of the deformable soft tissues. Overall, the present dissertation provided a novel experimental and FE modelling framework to investigate joint contact mechanics in the human knee joint. It is hoped that the validated subject-specific knee FE model can be used in future in vivo studies to explore knee joint biomechanical function, simulate different joint pathologies, assist clinical diagnosis and assess the likely outcomes of therapeutic treatments.
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ItemPost-traumatic knee osteoarthritis after anterior cruciate ligament reconstruction: Psychological, functional and biomechanical factors and the effect of a targeted brace( 2015)Post-traumatic knee osteoarthritis (OA) after anterior cruciate ligament reconstruction (ACLR) is prevalent in younger adults and has the potential to cause substantial knee-related symptoms and limit physical function. Physical and psychological impairments are likely to adversely affect quality of life and work participation. Knowledge of modifiable risk factors associated with knee OA post-ACLR has the greatest capacity to lead to new interventions that could change the natural history of knee OA. What are the modifiable factors associated with knee OA post-ACLR? Section A of this thesis describes the results of two cross-sectional studies which revealed that individuals with knee OA five to 12 years post-ACLR have worse knee confidence and greater kinesiophobia compared with individuals who have no OA five to 12 years post-ACLR. In individuals with knee OA five to 20 years post-ACLR, those with worse knee confidence have worse knee-related symptoms, poorer function, greater kinesiophobia, and poorer perceived self-efficacy and health-related quality of life. Section B of this thesis investigated knee biomechanics during walking in individuals post-ACLR. Pooled data from a systematic review revealed that, compared to healthy controls and uninjured contralateral knees, ACLR knees have abnormal knee biomechanics, particularly in the sagittal plane. Systematic review findings also revealed that the type of graft (hamstring or patellar) and time post-surgery could also influence knee biomechanics. A cross-sectional study also evaluated biomechanics in people with lateral knee OA post-ACLR. Compared to healthy controls, individuals with lateral knee OA five to 20 years post-ACLR had greater knee flexion and lower knee internal rotation angles, as well as greater pelvic anterior tilt, and hip flexion angles. Is there a potential intervention for modifiable risk factors associated with knee OA post-ACLR? A targeted knee brace was investigated for individuals with knee OA post-ACLR. First, a within-subject randomized study investigated the immediate and four-week effects of a targeted knee brace on knee-related symptoms and function in individuals with knee OA post-ACLR. The brace produced improvements in knee-related symptoms immediately and following four weeks of intervention. Second, a within-subject randomized study evaluated the immediate effects of varus bracing on gait characteristics in individuals with lateral knee OA post-ACLR. Results revealed that the unloader brace significantly altered gait characteristics associated with lateral knee OA post-ACLR. Overall, this thesis sheds light on some of the modifiable risk factors associated with knee OA post-ACLR, and investigated one targeted intervention with the potential to improve quality of life of individuals with knee OA post-ACLR. Targeting psychological, functional and biomechanical risk factors in individuals post-ACLR may aid in optimal recovery, and slowing disease progression in individuals with knee OA post-ACLR.