1. TWU Department of Kinesiology Denton, Texas TWU Biomechanics Laboratory TWU Biomechanics Laboratory TWU Biomechanics Laboratory Biomechanical Knee Risk Factors Between Horizontal and Vertical Landing Conditions M. Vining, A. Neally, K. Fuller, S. Lee, Y. H. Kwon ABSTRACT INTRODUCTION PURPOSE METHODS RESULTS CONCLUSIONS This study determines biomechanical risk factors for knee injury between horizontal and vertical landing conditions. To do so ground reaction force, knee orientation angle, and sagittal and frontal joint knee moment were analyzed. It was found that knee flexion angle was greater in the vertical direction, and varus knee moment, knee extension moment, and loading rate were all greater in the horizontal direction. This shows that the horizontal landing condition results in greater risk of knee injury. The purpose of this experiment was to determine the biomechanical risk factors for knee injury between horizontal and vertical landing conditions. Participants (n = 12) Twelve physically active females between the ages 18-25 participated. Procedure This experiment was performed using a 3D-motion camera system, reflective markers, and two force plates. The participants performed three trials of both the vertical and horizontal landing. The Vertical distance was 40cm. and the horizontal height was 91.44cm. Measurements Ground reaction force (GRF) using force plates. The magnitude of GRF was divided by time to determine loading rate. Knee orientation Angle/ Knee flexion angle, and sagittal and front knee joint moment using the Vicon 3D motion camera system. All measurements were analyzed using the Kwon-3D computer program. For each variable four events were analyzed: contact point, max vertical force, lowest point, and the end position. Importance: 6.6 million knee injuries were reported to United States emergency rooms from 1999 to 2008; 49.3% of which were sport related. Understanding knee injury risk in different landing positions in sports would help prevent knee injury. To assist in developing safer training skills to reduce risk of knee injury long term. Prevention of daily or work related injuries of the knee. Other studies have found: Increasing vertical height or horizontal distance increases ground reaction force (GRF) magnitude. Larger knee flexion angle reduces GRF and risk of knee injury. Horizontal landing results in greater GRF, lower knee flexion angle, and less knee moment. Vertical landing results in less GRF which usually results in lower knee flexion angle, causing less reliance on muscles and tendons for stability (less risk of injury). However, many studies have used peak GRF as a variable of risk, rather than the loading rate which better correlates with the amount of force being applied to the knee joint at a given time. Fig. 1: Horizontal Landing Condition DISCUSSION Fig. 2: Vertical Landing Condition Graph 1: The vertical component had a higher peak GRF, but the horizontal component had a greater loading rate. Graph 2: Moment was greater in the horizontal component than the vertical during the down phase (CO– LP). Graph 3: The horizontal component consisted of more varus torque while the vertical component consisted of more valgus torque. Graph 4: The vertical component produced greater knee flexion angle. Ground reaction force produced a higher peak in the vertical component, but there was a higher loading rate in the horizontal component. The greater horizontal loading rate creates a higher risk of knee injury because more force is applied to the knee joint over the landing time. For sagittal resultant joint moment, the horizontal component had greater joint moment about the medio-lateral axis during the down phase. The down phase (CO-LP) starts when the feet contact the floor and stops at the lowest point, just before extension begins. This higher joint moment results in more force being applied to the knee joint, increasing the risk of injury. For sagittal resultant joint moment, the vertical component had less joint moment about the medio-lateral axis during the down phase. Lower joint moment results in less force being applied to the knee joint which will result in a lower risk of knee injury. As the knee flexion angle increases, so does the joint knee moment in order to counteract the downward motion and high loading rate. The horizontal component produced a higher varus torque than the vertical component which increases the risk of injury. This is because varus movement puts the most force on the ligaments of the knee. Knee flexion angle was greatest overall in the vertical component. With this higher angle more force is absorbed at the knee joint which reduces the risk of knee injury. The horizontal landing condition resulted in a greater risk of knee injury because there was a higher loading rate, greater varus knee torque, and greater knee extension moment.