Total knee arthroplasty has been effective in reducing pain, but less so in restoring function, especially for activities requiring deep knee flexion. The philosophy of this dissertation was that more functionally effective and optimally designed artificial knees could be created for high flexion activities, if the knee joint kinematics and joint contact forces applied during finite element testing, knee simulator testing, and fatigue testing were more physiologically accurate. The objective of this work was to determine knee joint kinematics and contact forces that could be used in high flexion total knee replacement design and pre-clinical testing. Knee kinematics were determined during high flexion activities for total knee replacement patients and asymptomatic subjects by tracking the motion of skin-mounted sensors. In addition, a protocol was developed to determine the effect of soft tissue artefact on the accuracy of the skin-mounted sensor system in high flexion. The ranges of motion determined for the studied activities can be used as a benchmark to measure the functional success of high flexion total knee replacements. Tibiofemoral joint contact forces were estimated during high flexion activities of daily living using a simple, non-invasive, inverse dynamics based model. The accuracy of the joint contact force estimates was investigated by comparing the estimated forces to in vivo forces measured directly using implanted instrumented tibial components. The comparison showed that the model underestimates the measured axial joint contact force, most likely because the model neglects antagonistic muscle co-contraction. The measured and modeled joint contact forces and the measured knee kinematics could be used to form industry standards for knee simulator and fatigue testing to ensure that the implants are being tested physiologically. Healthy target populations can be studied using the methods outlined in this thesis to define testing standards for target populations: Kinematics can be determined as they were in this work for a group of Middle Eastern subjects, and the non-invasive inverse dynamics based model (with some consideration for the underestimation of forces) could be used to determine the tibiofemoral joint contact forces that the implant might be subjected to during activities of daily living. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2010-10-25 11:33:06.162

Knee osteoarthritis (OA) is a debilitating disease affecting the entire knee joint by inducing pathological changes to the cartilage and menisci. Currently, the etiology of OA is not completely understood. However, altered gait mechanics, specifically increased joint loading, of OA patients have a clear association with both symptomatic and structural OA progression. Non-surgical intervention tools, such as variable stiffness shoes (VSS), have been developed as a way to decrease loading within the knee joint. However, with external moments being surrogate measures for knee loading, it is unclear if changes in knee moments with the footwear are sufficient to result in a clinical benefit. Therefore, this project’s purpose was to investigate whether a VSS intervention can alter knee joint loading and menisci function in a knee OA population. We used gait analysis, musculoskeletal modeling, and finite element (FE) analysis to determine the effect of VSS on gait mechanics, knee joint contact force, and menisci stress and strain, compared to a control shoe. We found knee moments did not decrease with the VSS intervention. Furthermore, participants who did experience a decrease in knee adduction moment did not always experience a decrease in medial compartment contact force. However, results from our FE modeling of the tibiofemoral joint indicate significant changes in knee joint contact force can influence stress placed on the menisci. Results from this study suggest knee contact forces and tissue stress, not only external moments, should be considered when investigating if VSS can positively impact an OA population.