Influence of the difference of lower extremity alignment during single leg landing on knee joint stress

Abstract

We asked 12 healthy women to perform a single leg landing on a force plate from a 40 cm board with three lower extremity alignments, Neutral, Knee-in & Toe-out and Knee-out & Toe-in, and electromyographic data and ground reaction force were measured. The maximum muscle discharge and the integral of the rectus femoris muscle, the integral of the lateral vastus muscle and the ground reaction force to inside of the body in the conditions of Knee-in & Toe-out were significantly larger than those in Neutral. The ground reaction force to outside of the body in Knee-out & Toe-in was significantly large. The results show that by contracting the rectus femoris and lateral vastus muscles, the tibia is drawn out, and a shear force occures on the inside of the tibia in response to the ground reaction force received by the femur in the Knee-in & Toe-out condition. Thus we consider that ACL damage happens easily. In the Knee-out & Toe in conditions, we consider ACL damage can happen easily because in addition to raising the extension force on the ACL through rotation of the lower leg, a shear force occurs on the outside of the tibia in reaction to the femur.