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.