Biomechanical and Physiological Risk Factors for Anterior Cruciate Ligament Injury in Female Soccer Players: a Prospective Study
Elizabeth C. Letchford, MS, ATC
Background: Anterior Cruciate Ligament (ACL) injuries are common in female athletes and often result in long-term consequences due to the compromised integrity of the knee joint. The underlying mechanism responsible for ACL injury is likely a result of several different factors. No study has prospectively examined both physiological and biomechanical risk factors for injury and how the combination of risk factors may affect female soccer players. Additionally, limited information exists on the extent to which these factors change from pre to post season.
Research Aims: In order to create a comprehensive risk profile of the ACL-injured athlete, this study is being conducted with the following research aims: (1) To evaluate the biomechanical and physiological factors that are most influential in predicting risk for ACL injury in female soccer players age 14-25, (2) To investigate the ability of the LESS to identify risk for ACL injury in a high-school age female soccer population, (3) To evaluate the effect of participation in a single soccer season on changes in biomechanical and physiological variables.
Methods: The investigation will be a prospective cohort study of 200 female high school and collegiate soccer players. Players will be screened for biomechanical and physiological risk factors for ACL injury at the beginning and end of the playing season. Updates to lifestyle factors will be collected via monthly questionnaires. Multivariable logistic regression will be used to model the association between risk factors and ACL injury, controlling for confounding factors. Comparisons between pre and post-season findings will be evaluating using a paired t-test.
Significance and Innovation: Prior studies of ACL injury risk were limited by small sample sizes, retrospective analyses, limited generalizability, and failure to recognize the effects of confounding variables. The proposed study design includes a series of prospective investigations that will examine multiple factors and their combined effects on risk for ACL injury. The goal is to build a comprehensive profile of the non contact injured athlete in order to help create a better screening tool to decrease the instance of ACL injury in female athletes.
Each year, over 200,000 Anterior Cruciate Ligament (ACL) injuries occur in the United States and often result in long-term consequences due to the compromised integrity of the knee joint 1,2. Female athletes have up to 6 times higher incidence of ACL injury than male athletes of the same sport involvement 2,3. Despite consistent investigation, the precise mechanisms responsible for non-contact injury continue to remain ambiguous and prevention programs continue to fail to reduce the instance of ACL injury. The overall goal of this prospective cohort study is to build a comprehensive profile of the non-contact ACL-injured athlete in order to create a more effective and comprehensive prevention protocol to better recognize those athletes who may be at high risk for ACL injury.
Eligible female soccer players (n=200) will be recruited from the greater San Francisco and greater Honolulu, Hawaii areas. Data collection will occur at the beginning of the athletic season and include measurements of physiological (Iron, Vitamin D, Cortisol) and biomechanical (LESS scores, shoe type, surface type) variables. Instance of ACL injury will be confirmed by a physician and reported to the investigators. An identical data collection procedure will be conducted on the un-injured subjects at the conclusion of the competitive season. Markers for ACL injury in injured subjects will be compared with those of uninjured subjects to determine the correlation of each marker with instance of ACL injury. Comparisons will be made between pre-season data and post-season data on un-injured subjects to evaluate the extent to which these predictive risk factors may change over the course of a playing season. Significant biomechanical and physiological predictors of injury will be used to create a prediction equation to best identify risk for ACL injury in female soccer athletes.
Specific Aim #1: To evaluate the existence of a correlation between physiological and biomechanical risk factors and instance of ACL injury.
Hypothesis #1: Compared to subjects who do not sustain an ACL injury, ACL-injured subjects will have higher levels of Iron insufficiency, Vitamin D insufficiency, increase in markers for inflammation ( IL-6) and higher LESS scores during the pre-season evaluation.
Specific Aim #2: To investigate the ability of the LESS to identify risk for ACL injury in a high school age female soccer population.
Hypothesis #2: Among high-school age female soccer players, there will be an positive relationship between LESS score and incidence of ACL injury.
Specific Aim #3: To evaluate the effect of participation in a single soccer season on changes in biomechanical and physiological variables.
Hypothesis #3: Biomechanical and physiological variables change from the beginning to the end of a single soccer season.
Strengths of the study include prior experience with recruitment and follow-up of the study population, the racial/ethnic diversity of the population, the use of multidimensional risk factors (physiological and biomechanical) for ACL injury and collaboration among a team of scientists representing multiple disciplines. By combining the expertise of laboratory-based investigators with clinical-based investigators, this study offers the opportunity to investigate a much wider range of risk factors. Additionally, this collaboration allows for access to compare the laboratory-based results with the clinically based results in order to create the most effective injury-screening tool that is clinically applicable. This study is innovative in that it will be the first to build a comprehensive profile of the non-contact ACL-injured athlete in order to create a more effective and comprehensive prevention protocol to better recognize those athletes who may be at high risk for ACL injury. The significance of the study lies in the fact that creation of a more accurate profile of the non-contact ACL-injured athlete may allow for more comprehensive injury prevention practices leading to a decrease in the risk of ACL injury in female soccer athletes.
Supporting Studies to be conducted by University of Hawaii Graduate students separately from the current study:
1. Validating the Landing Error Scoring System for use with female soccer athletes age 14-25
Scores measured via the LESS will be compared with scores measured through a simultaneous three-dimensional motion capture system.
2. Evaluating neurocognitive deficits as a risk factor for lower extremity injury in high school athletics.
Pre-season cognitive baseline measurements (IMPACT) will be evaluated as a risk factor for lower extremity injury in contact sports over the course of a single high school athletic season.