Evaluation of Lower Extremity Energy Absorption Strategies in Adolescent Males and Females with and without an ACL Injury

Abstract

Introduction: Anterior cruciate ligament (ACL) injuries are the most common ligamentous injury in the adolescent knee, resulting in long-term health consequences including early onset knee osteoarthritis and a high predominance of re-injury. The current ACL rehabilitation measures need improvement, in particular for adolescents. Information surrounding energy absorption strategies during demanding tasks may provide important insight into functional capacity and movement quality and could be a variable that is considered in ACL rehabilitation programs. The purpose of this thesis was therefore to evaluate energy absorption strategies in adolescent males and females with and without ACL injuries. Specifically, to first identify sex and injury status differences in lower extremity kinematics and kinetics in adolescent males and females with and without an ACL injury, and then secondly, determine if there is a generalizable relationship between strength and energy absorption strategies within these populations during drop-vertical jumps. Methods: Fifty-two ACL injured (17 males) and 68 control adolescent (34 males) males and females between the ages of 10 and 18 performed five trials of a lunge and drop vertical jump (DVJ) task. Ankle plantarflexion, and knee extension and flexion maximum voluntary isometric contractions (MVIC) were collected, along with 3D kinematics and kinetics including joint angles, joint moments, and energy absorption at the hip, knee, and ankle joint. Two-way analyses of variance (ANOVA), statistical non-parametric mapping (SnPM), and multiple linear regressions were used to determine statistically significant differences and relationships in joint kinematics, kinetics, and MVIC's between the male and female ACL injured and control individuals. Results: Males displayed greater knee extension torque compared to females, while controls displayed greater knee extension and ankle plantarflexion torque compared to ACL injured. There were no energy absorption differences found during the DVJ, however, during the lunge male controls display greater energy absorption compared to females. Furthermore, small effect sizes were found in the hip, knee, and ankle joint energy absorption for knee strength (knee extension or knee flexion), sex, and injury status. However, sex, injury status, and knee strength did not significantly add to the prediction of energy absorption. Conclusion: These findings indicate that isometric strength might be an important variable to be considered in ACL injury rehabilitation and injury prevention programs with injured individuals displaying weaker knee extension and ankle plantarflexion torques. However, energy absorption may not be as important of a variable to consider as there were limited statistically significant differences between injury status and sex at the hip, knee, and ankle joints. Additionally, there does not appear to be a generalizable relationship between hip, knee, and ankle energy absorption and knee flexion and extension isometric strength in male and female control and ACL injured individuals. Injured individuals absorb similar energy levels at each joint compared to controls, with isometric strength showing a weak relationship with energy absorption. Therefore, it is possible that there is not a specific energy absorption or muscular strength strategy that can be used to improve adolescent ACL rehabilitation measures.