The Influence of Sports-Related Concussion on Lower Extremity Injury Risk in Adolescent and Collegiate Athletes

Sports-related concussion (SRC) represents a major epidemiological concern in the adolescent and collegiate athlete populations, with conservative estimates of approximately four million SRCs occurring each year in the United States. While the majority of previous research has emphasized the management and recovery of the cognitive aspects of SRC, recent data indicates subtle motor behavior is altered following a concussive event. Injury surveillance literature indicates that adolescent and collegiate athletes are at an approximately 2–4 greater risk for lower extremity (LE) injury following an SRC when compared to matched controls and pre-SRC LE injury rates. Furthermore, athletes with a previous SRC history are sustaining high rates of LE injuries at time periods well-beyond clinical clearance to resume sport, in certain cases upwards of one year after SRC occurrence. However, the biomechanical and cognitive mechanisms that underpin the relationship between SRC and LE injury have yet to be fully elucidated by the present literature. Further study of sport-specific tasks, in conjunction with cognitive performance markers, is necessary to provide a mechanistic rationale as to why athletes with SRC histories are sustaining LE injuries at a greater rate than controls. Therefore, multiple literature reviews (Chapters 1–3) were warranted to orient the reader to the current knowledge base surrounding SRC and its associations with LE injury risk. The purposes of the literature reviews were as follows: 1) to provide a comprehensive overview of the current literature relating to SRC; 2) to examine current SRC management strategies and their utility in identifying concussed athletes at-risk for LE injury; and 3) to systematically investigate the influence of cognitive performance on LE injury risk. The overall purpose of these dissertation studies was to identify whether adolescent and collegiate athletes with and without an SRC history demonstrated differences in LE biomechanics and cognitive performance during sport-specific jump-landing maneuvers. Additionally, this dissertation sought to identify biomechanical and cognitive predictors of SRC injury history in collegiate athletes. This dissertation utilized common LE biomechanical and cognitive testing tools to assess whether previously concussed adolescent and collegiate athletes were at greater risk for LE injury compared to non-concussed controls. The first study (Chapter 4) examined group differences in drop-landing biomechanics in adolescent athletes with and without an SRC history. LE kinematic and kinetic patterns previously associated with LE injury risk during landing tasks were measured and it was determined that previously concussed adolescents performed drop-landings with significantly less sagittal plane landing motion versus controls. In the second quantitative study (Chapter 5), the associations between LE landing biomechanics during a land-and-cut task and cognitive performance on various assessments were measured in a collegiate athlete cohort with and without an SRC history. Pearson correlation coefficients indicated significant associations between functional visuomotor reaction time and peak knee flexion, as well as associations between knee abduction moment and computerized cognitive performance, only in collegiate athletes with an SRC history. In the final study (Chapter 6), LE landing biomechanics were measured in collegiate athletes with a previous SRC history and healthy matched controls during a reactionary jump-landing maneuver. Additionally, cognitive performance was measured with a battery of clinical and functional tasks in both cohorts. Group-based (ANOVA) and predictive modeling (binary logistic regression and a C5.0 decision algorithm tree) were implored to identify the most relevant LE landing biomechanics and cognitive performance variables associated with SRC history. Compared to the control cohort, previously concussed collegiate athletes demonstrated significantly less knee flexion on both dominant (DOM) and non-dominant (NDOM) limbs during the land-and-cut tasks. Additionally, Multiple Object Tracking score and knee flexion (binary logistic regression) as well as Verbal Memory, knee flexion, and Go / No Go total score (C5.0 decision tree algorithm) were identified as the strongest indicators of previous SRC injury history. In summary, this dissertation utilized a multifaceted approach to identify subtle biomechanical and cognitive mechanisms in previously concussed athletes that may provide an objective rationale for the relationship between SRC and future LE injury risk. Specifically, adolescent and collegiate athletes performed landing tasks with significantly less sagittal plane motion versus control athlete, suggesting a potential biomechanical mechanism for LE injury after an SRC. Additionally, worsening performance on cognitive measures of working memory and attentional capacity were indicative of a previous SRC history. The present findings suggest clinical management of an SRC should incorporate specific assessments to monitor both motor and cognitive performance in concussed athletes. Future research should examine both pre- and post-SRC biomechanical performance during sport-specific tasks with an imposed cognitive load to further our understanding of LE injury risk in athletes who sustain an SRC