Ambulatory evaluation of 3D knee joint function in patients with ACL rupture using inertial sensors

In orthopaedics, outcome evaluation is currently recognized as a major challenge to improve the knowledge both about injuries and treatments. For anterior cruciate ligament (ACL) rupture, various evaluation tools are available for routine uses: clinical examinations, static knee joint laxity measurements and scores. Although these tools can diagnose an ACL rupture and evaluate the results of a surgery, they are inadequate to answer the current therapeutic issues. Therefore, since two decades, gait analysis was investigated as an objective evaluation approach to quantify more subtle kinematics modifications. However, these analyses need dedicated laboratories including complex and expensive devices for motion capture. Consequently, only few studies focusing on ACL were conducted up to now. These studies enrolled a limited number of patients and reported partly divergent results. Thus, nowadays, surgeons lack a reliable, objective and simple method to evaluate the three-dimensional (3D) knee joint function in field during daily activities and conditions. In this thesis, we propose and assess new devices and algorithms to fulfil these needs. The contributions are driven by four main objectives: to provide appropriate measurement systems, to ensure repeatable quantification according to clinical descriptions, to determine the suitability of the kinematic parameters for outcome evaluation, and to use these new tools in clinical applications, both to show their relevance and provide new insights about the lower limb 3D function. Measurement systems. Three devices are designed in this thesis. The first device consists of a portable data logger and two 3D gyroscopes fixed on the thigh and the shank segments. It quantifies the 3D function of the knee joint. The second system fuses 3D gyroscopes with 3D accelerometers in order to measure the orientations during short periods. By strapping several of these sensors units on the lower limb segments, this system allows ambulatory measurement of 3D kinematics. Finally, an original system combining a portable magnetic tracker and inertial sensors is proposed to measure body segments orientation over long durations. The performances of all systems are assessed against high level reference devices. Functional calibrations. In order to quantify the 3D function of the knee joint independently of the sensors location on the segments, calibration methods suitable for the inertial-based systems are proposed. These methods follow the recommendations of the International Society of Biomechanics (ISB) and avoid the localization of anatomical landmarks. They rely on predefined movements and posture measurements. The angular displacements obtained through these functional calibration procedures when collecting the data with one of the proposed system are positively comparable to previous systems in the literature. Kinematic parameters characterisation. Before using any data to quantify kinematics changes induced by an injury or a treatment, it is essential to evaluate their reliability. The propagation of both, anatomical-based and functional calibration procedures errors to 3D kinematics is investigated. The repeatability of the parameters is also evaluated. Finally, the effects of soft tissues artefacts are estimated using an exoskeleton harness. Clinical applications. The evaluation methods proposed here are involved in three different clinical protocols, both to evaluate their convenience of use and to contribute to the increase of clinical knowledge. Two applications enrol ACL-deficient patients prior and following reconstructive surgery, and a third one considers four groups of patients with various ankle conditions. During these studies, long distance ground level, and incline walking activities are monitored. This thesis proposes original inertial-based methods to evaluate the 3D function of the knee joint. The measurement errors are comparable to those of standard in lab devices, while the new systems allow ambulatory monitoring in clinical field. The characterization of the kinematic parameters confirms the value of the literature when existing. Finally, the clinical applications report promising results and validate the suitability of the methods for routine uses.