The purpose of this study was to increase knowledge about the landing posture that induces anterior cruciate ligament (ACL) injury. Analysis was done to determine the knee abduction moment during single limb landing using our previously proposed mathematical model. Our model has proven that the criterion of knee abduction occurring is when the acting line of the ground reaction force is directed laterally to the lower leg segment. Based on this, we predicted a medial shift of the knee joint and a lateral leaning of the trunk segment to induce the knee abduction moment. To verify the results of our model prediction, we conducted a motion analysis experiment with a single limb-landing task. Three male and four female subjects participated in the experiment. Subjects were instructed to fall from a 30 cm high box and land on a target which was assigned by PC-controlled laser pointers. Since the landing target was unexpectedly moved during landing, the subjects were perturbed and exhibited various landing postures. The results of the landing experiment showed that trunk leaning laterally towards the landing limb and medially shifted knee alignment induced the knee abduction moment. These results are consistent with the results predicted by our model. In conclusion, appropriate control of both lower limb alignment and trunk motion in the frontal plane in essential for reducing the risk of ACL injury.

The aim of this study is to examine the potential of the two-dimensional posture evaluation method as a screening tool for detecting the high-risk population for anterior cruciate ligament injury.Eleven healthy adults participated in this study. They jumped from a 31 cm-high box and landed on their dominant leg. Three-dimensional knee flexion/extension, knee valgus/varus and hip adduction/abduction angle during single-legged landing were calculated. At the same time, the Frontal-plane Knee Displacement index (FKD)-the knee joint position relative to the line between the hip and ankle joint-was measured.FKD reflects the time variation of three-dimensional knee valgus and hip adduction angle very well.Our results suggest that FKD has potential as a screening tool particularly for movement occurring primarily in the frontal-plane.

The higher anterior cruciate ligament (ACL) injury rate of females is one of the most sever athletic-related problems today. The purpose of this study is to compare the lower extremity kinematics between male and female during single leg landing.Six male and four female healthy subjects participated in this study. They jumped from a 32 cm high box and landed with the dominant leg. The landing action was filmed with three video cameras. The knee flexion, knee valgus/varus, and hip adduction/abduction angle and angle velocity were calculated.In female subjects, the knee flexion angle and hip adduction angle were greater compared to males. Also, the knee valgus velocity and hip adduction velocity were higher in females.Our results suggest that knee valgus kinematics may be related to hip adduction. It is important to evaluate hip kinematics when considering knee kinematics to prevent knee ligament injuries.