Proximal Tibia Anterior Shear Force in Stop-Jump Tasks

Abstract

Introduction: Anterior cruciate ligament (ACL) injuries are common in sports. The majority of ACL injuries involve no or little direct physical contact between athletes when injuries occur. Female athletes injure their ACLs at four to eight times the rate of male athletes depending on the sport and level of training. Recent studies found that ACL injuries frequently occur in stop-jump related tasks performed in sports such as soccer, basketball, and volleyball. Athletes in these sports frequently perform stop-jump tasks and have an increased incidence of lower extremity injury, including ACL injuries in comparison to other sports. The purposes of this study were (1) to compare selected knee kinetics and kinematics between male and female recreational athletes in three stop-jump tasks: forward stop-jump task, vertical stop-jump task, and backward stop-jump task; and (2) to determine the relationship between selected knee kinetics and kinematics that may contribute to the risk for non-contact ACL injuries. Methods: Seventeen male and Seventeen female healthy recreational athletes volunteered to be subjects for this study. Two Bertec 4060A force plates (Bertec Corporation, Worthington, OH) were used to collect ground reaction forces and moments at a sampling rate of 540 Hz. Four video cameras were used to record each subject's performances during the experiment at a frame rate of 180 frames/second with setup for the Direct Linear Transformation procedure. Each subject performed five successful trials for each task. Three-dimensional coordinates of reflective markers on body landmarks and ground reaction force data were collected in each trial. Lower extremity joint centers were estimated from the coordinates of reflective markers. Joint resultant forces and moments at the knee on the tibia were estimated using an inverse dynamic model. The estimated knee joint resultant force and moment vectors were translated to the tibia reference frames. The peak proximal tibia anterior shear force during landing of each task was identified. The knee flexion-extension moment, valgus-varus moment, and knee flexion angle at the peak proximal tibia anterior shear force were also determined. Two-way analyses of variance with mixed design were conducted to compare the selected knee kinetics and kinematics between genders and tasks. A multiple regression analysis was conducted to determine the relationship between peak proximal tibia anterior shear force and other selected knee kinetics and kinematics. Results: Female subjects had significantly greater peak proximal tibia anterior shear force, knee extension moment, knee valgus moment, and smaller knee flexion angle than male subjects (p = 0.00). Task did not significantly affect the knee flexion-extension and valgus-varus moments at the peak proximal tibia anterior shear force. Task also significantly affects the knee flexion angle at the peak proximal tibia anterior shear force (p = 0.00). Peak proximal tibia anterior shear force was significantly correlated to the knee flexion-extension moment and knee valgus-varus moment with an overall regression determinant of r2 = 0.52 (p = 0.00). Discussion: The results of this study provide significant information related to the risk factors and possible prevention of non-contact ACL injuries. Proximal tibia anterior shear force has been identified as a major contributor to the anterior tibia translation, a motion resisted by the ACL. An increased proximal tibia anterior shear force is likely to increase the strain on the ACL and increase the risk of ACL injuries. The altered lower extremity neuromuscular motor controls in risky tasks are likely to be an important contributor to the increased risk for non-contact ACL injuries in women. An increased knee extension moment can be considered as an indication of an increased quadriceps force or decreased hamstring force. Knee varus-valgus moment can also be considered as the rotation effect generated by the muscle contractions across the knee joint. The significant correlation of these two knee kinetic measures to the peak proximal tibia anterior shear force indicates that the increased peak proximal tibia anterior shear force in female subjects is likely due to altered lower extremity motor controls. Women's altered lower extremity neuromuscular motor controls may bring them close to those awkward body positions or uncoordinated motions and increase their risk for non-contact ACL injuries. Technical training to correct altered lower extremity neuromuscular motor controls may assists in preventing non-contact ACL injuries by keeping athletes away from awkward body positions and uncoordinated motions.