Abstract: The aim of the invention is to make improvements to the “GNRB®” device for detecting and following up an ACL injury, one improvement comprising a system for positioning the knee at a flexion of 20° to 90°, characterized by two separate seat portions which are pivotable relative to one another (300 and 400) and by a system for measuring the angle of the pivotal movement, and another improvement comprising a foot-supporting assembly (200), characterized by two portions, one of which is movable relative to the other on a shaft of a rotation sensor (204). The device according to the invention enables the seat of the ACL injury to be identified in the event of a partial tear (PL bundle or AM bundle) and enables the rotational instability of the knee to be measured during the translational movement of the tibia relative to the femur.