Biomechanical characteristics of an anterior cruciate ligament injury in javelin throwing

The purpose of this study was to understand the mechanism of an anterior cruciate ligament (ACL) injury in javelin throwing and javelin throwing techniques relevant to this ACL injury. The patient in this study was an elite female javelin thrower who completed the first three trials and sustained a non-contact ACL injury on her left knee in the fourth trial of javelin throwing during a recent track and field meet. Three-dimensional kinematic data were collected in the injury and non-injury trials. The kinematic data of 52 male and 54 female elite javelin throwers were obtained from a javelin throwing biomechanical database. The patient had greater forward center of mass velocity and less vertical center of mass velocity after the first 25% of the delivery phase in the injury trial compared to non-injury trials. The patient had less left knee flexion angle and angular velocity but similar left knee valgus and internal rotation angles during the first 21% of the delivery phase in the injury trial compared to non-injury trials. The video images showed an obvious tibia anterior translation at the 30% of the delivery phase in the injury trial. The left knee flexion angle and angular velocity at the time of the left foot landing and the maximal left knee flexion angle during the delivery phase were not significantly correlated to the official distance for 52 male and 54 female elite javelin throwers. The ACL injury in this study occurred during the first 30% of the delivery phase, most likely during the first 25% of the delivery phase. A stiff landing of the left leg with a small knee flexion angle was the primary contributor to this injury. Javelin throwers may have a soft left leg landing with a flexed knee, which may help them prevent ACL injuries without compromising performance.