ACL injuries occur when an athlete rapidly decelerates, followed by a sharp or sudden change in direction. In order to improve surgical results and understand the disease, it is necessary to evaluate how kinematics of the knee changes. Rotational instability in ACL insufficient knee addresses the symptom or the abnormal motion, which can be subjectively evaluated in the clinical exam. The clinically available quantitative measurement for this instability has not been established, and this prevents providing the definite diagnosi. In order to solve the problem, a measurement system for 6 degree of freedom in knee motions has been developed. This system consists of two plates connected by six linear potentiometers that expand or contract to fit the knee movement. By using this system, the pivot shift test was evaluated in the ACL injured knee.
