Motion analysis of the knee : Kinematic artifacts, EMG normalisation and joint forces

Sammanfattning: The non-contact anterior cruciate ligament (ACL) injury is the most common and serious debilitating knee joint injury in male and female athletes. To create an ACL injury paradigm that will lead to improved treatment and prevention it is necessary to understand how ACL injuries occur. Currently this information is lacking for reasons such as differing methodologies used in studies of neuromuscular control of the leg muscles, lack of information related to the role of sports equipment in affecting knee joint forces, and insufficient measurement accuracy of 3D knee joint kinematics. The aim of this thesis is to address some of these issues by: (1) evaluating techniques of electromyography (EMG) analysis with ACL patients; (2) investigating the contribution of sports equipment to reducing knee joint forces in skiing; (3) assessing the accuracy of non-invasive motion analysis techniques in measuring true bone motion and verifying techniques to improve the accuracy. We identified that EMG normalisation methods would significantly affect the ability to detect neuromuscular alterations between injured and non-injured leg muscles in ACL injured subjects. We found that clinical outcome measures of neuromuscular control were dependant on normalisation and that the MVC method was most sensitive at detecting injured to non-injured limb neuromuscular alterations. We also provided evidence of reduced gastrocnemius muscle activity in ACL injured patients. We found that the release and rotation of the ski boot cuff both increased knee joint compressive force and reduced anterior shear force. The important role of sports equipment in contributing to injury prevention was established. Finally, by measuring in-vivo tibio-femoral motion and comparing it with noninvasive skin marker techniques we found average rotation errors of 4.4 degrees and 13.1 degrees and translation errors of 13.0 and 16.1 mm for rotations during walking and cutting respectively. Skin markers did not accurately reflect tibio-femoral joint motion. The error introduced due to skin movement artifact affected both the magnitude and direction of reported tibio-femoral motions during the walk and cut. Although we were not able to improve the measured kinematics by reducing intermarker movements, we have proposed a standard error of measurement to be used when reporting knee joint motion data in the future. We believe that the content of this thesis provides a solid foundation from which to build an ACL injury paradigm and provides insight into factors associated with performing motion analysis of the knee.