The anterior cruciate ligament (ACL) is most commonly injured during sporting activities such as football, ski, handball etc., when an athlete suddenly pivots or places excessive rotational force on his knee. The ACL can also be torn during severe trauma such as a car accident or as the result of a work injury. Switzerland’s primary accident insurer reports more than 3500 ACL injuries per year. An ACL injury generates knee instability which increases the risk of disease in menisci and cartilage and affects the performance of daily activities. Several studies have shown that injuries of the ACL affect the performance of daily activities. However the three dimensional (3D) knee kinematic after ACL injury and/or surgery and particularly during daily activity is not clearly understood. Moreover, it’s not certain that surgery can restore the complex kinematics of the knee. The purpose of this study was two folds: to develop an ambulatory system which enables 3D knee kinematic evaluation during daily activities and to characterize the knee kinematics in order to compare the deficient ACL with the healthy one. We aimed to provide a new tool for objective outcome evaluation and functional assessment of patients with knee ligaments pathology, a tool that can be used easily by any physician at the hospital or in his office and moreover by the patient himself at home. It will allow measurement of changes in the biomechanics of the knee by noting the effects of these changes on clinical findings and day-living patient activity