Predictors of Anterior Shear Force During Reactive and Planned Jumps

Abstract

1574 Jumping and landing tasks combined with a deceleration component have been implicated as a mechanism of noncontact ACL injury. To date, researchers have studied these movements in controlled laboratory tests with the intent of determining at-risk movement patterns for noncontact ACL injury. It is not known whether these same movement patterns are observed during reactive tasks designed to simulate tasks similar to those implicated as a potential cause of injury. PURPOSE: To compare the neuromechanical characteristics between a planned and reactive stop-jump task, and to determine which characteristics would predict anterior shear force. METHODS: A neuromechanical analysis of the knee was conducted on 19 male and 17 female, healthy basketball players (Age: 16.1 ± 1.3 years) while performing planned and reactive vertical stop-jump tasks. For the reactive jump, subjects were required to react to a visual cue during the approach jump that provided the direction they were to jump after the initial landing on the force plates. For the planned jump, subjects were instructed to jump vertically prior to the initiation of the task. Knee flexion and valgus angle; knee flexion and valgus moment; anterior shear force; posterior ground reaction force; and EMG activity of the vastus lateralis and medial hamstrings were analyzed during the initial landing of the reactive vertical stop-jump. Independent t-tests were used to compare neuromechanical variables between jumps and separate stepwise multiple linear regression procedures were used to determine which of these characteristics would predict anterior shear force for each type of jump. RESULTS: Individuals demonstrated a decreased knee flexion angle, a decreased knee flexion moment, and an increased peak posterior ground reaction force during the reactive jumps (p<0.05). Posterior ground reaction force, knee flexion moment, and EMG activity of the vastus lateralis were significant predictors of anterior shear force for both jumping tasks (p<0.05). Knee valgus moment was also a predictor of anterior shear force during the planned jumps (p<0.05). CONCLUSION: Individuals utilized different movement patterns during the reactive jumps that better simulated actual athletic competition. These movement patterns include landing in less knee flexion with a greater deceleration component. The results suggest that reactive jumps should be included in research protocols when trying to determine the at-risk movement patterns for noncontact ACL injury. Supported by the Jewish Healthcare Foundation