High flexion kinematics and kinetics for the improvement of artificial knee joints
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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.