The Effects of Anterior Cruciate Ligament Thickness, Knee Joint Laxity, Activity Level, Neuromuscular Imbalances and Lower Extremity Muscular Activation Patterns on Anterior Cruciate Ligament Loading

There are numerous known mechanisms of anterior cruciate ligament (ACL) injury risk that span from knee joint laxity to landing mechanics. However, the relationship of these mechanisms to ACL loading during landing is unclear. In addition to landing mechanics, anthropological aspects such as ACL diameter, which can now be obtained via ultrasound, may also be an important mechanism for ACL loading. However, the relationship between ACL diameter to ACL loading and landing mechanics remains unknown. This study was conducted with three primary purposes. The first purpose of this study was to examine the inter and intra-rater reliability of using ultrasound to measure the diameter of the full ACL and anteromedial bundle of the ACL. The second purpose was to examine the relationship between the anteromedial bundle diameter and lower extremity strength, whole body anthropometrics, and previous physical activity levels. The third purpose was to examine the relationship between simulated ACL loading and pre-activation electromyography of lower extremity muscles, anteromedial bundle diameter and knee joint laxity. Two separate raters with differing levels of experience (low: Rater 1 and moderate: Rater 2) used diagnostic ultrasound to image bilateral ACLs of twenty participants. Rater 1 also performed an additional imaging session with the same population. Interclass correlations were conducted to examine 1) intra-rater reliability between sessions for Rater 1 and 2) inter-rater reliability between the Raters 1 and 2. To address the second purpose of this study, anteromedial bundle diameter, height, weight, strength measurements of the knee flexors, knee extensors, hip abductors, and hip adductors and previous physical activity were recorded for 17 participants. Pearson product correlations were conducted between anteromedial bundle diameter and the recorded variables. To address the third purpose of this study, 17 participants\u27 pre-activation of lower extremity muscles, anteromedial bundle diameter and passive knee joint laxity were recorded. Next, participants performed single leg landings from a 40 cm height and a height equal to their maximal jumping capabilities. During landings, three dimensional kinematic and kinetic variables were recorded as well as electromyography (EMG) of the Rectus Femoris, Vastus Medialis, Vastus Lateralis, Medial Hamstring, Lateral Hamstring, Medial Gastrocnemius, and Gluteus Medius. Participant specific musculoskeletal models were generated for each participant. Three dimensional ACL loading was calculated using previously established equations. Pearson product correlations were then utilized to analyze the relationship of ACL loading to knee joint laxity, anteromedial bundle diameter and pre-activation of the lower extremity muscles. Moderate correlations were found for inter and intra-rater reliabilities. There were weak correlations found for the full ACL diameter during inter and intra-rater analyses. The current results show that the anteromedial bundle can be found and measured more reliably than the full ACL. There were no significant correlations between anteromedial bundle diameter and previous exercise activity levels. However, significant correlations were found with quadriceps and adductor strength values. Simulated ACL loading was only found to have significant correlations with lateral hamstring pre-activation for both 40 cm and relative drop landing heights. The current results suggest that the pre-activation of the hamstrings may influence ACL loading if the medial and lateral hamstring groups are activated disproportionately. The results from these studies establish that the anteromedial bundle can be analyzed with moderate reliability from researchers utilizing ultrasound. Future research involving diagnostic ultrasound should consider analyzing the anteromedial bundle to increase reliability and generalizability of their results. Although it may be possible for stressors to cause hypertrophy in the ACL, few factors known to stress the ACL are significantly associated with the size of the anteromedial bundle diameter. Thus, the association between those mechanisms and ACL loading may not be as clear