A Mechanical Analysis of Lachman Test Using a Quantitative Measurement System with Force Sensor

The anterior cruciate ligament (ACL) is one of strong ligaments in the knee. The ACL has a role to prevent excessive internal rotation and forwarding movement of the tibia. The ACL reconstruction often occurs while doing sports. Lachman test is one of manual tests for examining the ACL. An examiner discriminates an injured degree of the ACL by feeling his/her finger stress. Rapidly stop motion during the Lachman test which is called as Endpoint, should be examined. Some measurement devices for Lachman test have been reported. However, these devices aim to analyze not the stress but a motion of the knee joint. Therefore, we set the goal of this study to develop a measurement system for the finger stress with force sensor during Lachman test. A quantitative measurement system during Lahcman test with force sensor was developed. Control method that was proposed to adjust sensor initial value for finger thickness by using fuzzy control was experimented to confirm the usefulness. Basic experiment before numerical analysis of Endpoint was revealed that the inclination of force can separate characteristic of string and elastic. Lachman test was measured by nine experts and one non-expert with this system. The five analyzed results of nine examiners were consistent with the estimated bimodality. It implies that the proposed analysis method and system have usefulness because they can estimate the bimodality from the measurement data in half of the all data. This study focused on not the injured knee but the normal knee. A future work is to apply this system to the injured knee.