Anterior cruciate ligament (ACL) ruptures are one of the most common knee ligament injuries suffered by both male and female athletes. These injuries are severe in nature and also have long-term impacts on activities of daily living. Significant research has been conducted utilizing a drop landing task to attempt to better understand the mechanics behind the injury and to help identify at-risk athletes for targeted intervention. However, there have not been any published standards for the height of the drop landing activity, and previous researchers have also raised some concerns about the ability of a drop landing task to replicate the landing mechanics of a sport-specific task. To examine possible differences in performance based on specific landing tasks, the first study compared the landing mechanics of male and female high school athletes in three different landing conditions (drop landing, DL; adjusted height drop landing, AHDL; and a vertical jump task, VJL) (Chapter 3). Thirty-seven (37) athletes completed bilateral landings in the three conditions, and their kinetic and kinematic landing mechanics were compared across conditions. For the male participants, maximum knee flexion during landing was greater in AHDL condition as compared to the DL and VJL conditions. Both male and female participants demonstrated greater hip adduction at impact and overall maximum value in the VJL condition as compared to the two drop landings. As drop landing tasks have been used to identify at-risk athletes, it was important to examine the three different tasks’ ability to predict lower extremity ligamentous injuries, and whether those 3D motion analysis predictors were more precise than a quick clinical symmetry screening tool (Chapter 4). One-hundred-and-sixty-five (165) athletes completed the clinical symmetry screen, and a subgroup of thirty-seven (37) athletes completed the 3D motion analysis. All of these participants were surveyed for lower extremity ligamentous injuries over the course of a season. Due to a small number of reported injuries, none of the injury predictor models based on 3D motion analysis landing mechanics or the clinical symmetry screening tool were able to produce accurate predictor models of injury. Knee abduction moment has been shown to be one of the strongest predictors of ACL injuries, and due to the collection of bilateral kinetics for a previous study (Chapter 3), there was a need to examine differences in KAM between the three different landing tasks (Chapter 5). Ten (10) recreational athletes completed bilateral landings in the three conditions, with foot placement relative to force plates to enable KAM calculation. The participants did not demonstrate any difference in KAM between the three landing conditions; however, a test for constant variance showed that the AHDL resulted in significantly less variance in KAM than DL or VJL. The results of these studies suggest that while easy to standardize, a set height drop landing task does not produce identical landing mechanics to those from an adjusted height drop landing task or a vertical jump task. Further research is needed to create or justify standardized landing tasks for researchers to utilize that produce consistent results that best duplicate the landing mechanics athletes performed during sporting activities. While the landing mechanics demonstrated in the three tasks and the results from the clinical screening were not able to predict injuries, future studies should examine quick clinical screening tools to identify athletes at a high risk of injury.

The use of wearable sensors in consumer health and medicine is a rapidly developing topic of interest. The main purpose of the series of studies in this thesis is to identify novel uses of technology that can provide clinicians and scientists clinically feasible, low cost approaches to obtain meaningful information about functional limb symmetry in patients with knee injuries. In Study 1, individuals undergoing knee surgery were evaluated as they walked and stepped down onto a force platform in a manner similar to how one would step off a curb to cross a street. When subjects stepped onto their uninvolved leg, peak vertical ground reaction force was greater and occurred earlier than when stepping onto their involved leg. Asymmetries were greater in those with higher quadriceps neuromuscular impairment. In Study 2, the reliability and validity of using wearable accelerometer sensors was evaluated for estimating single leg vertical hop height in healthy people and individuals after ACL reconstruction surgery. The reliability and concurrent validity of using accelerometers to estimate single leg hop height were excellent, and were similar for healthy and ACL-reconstructed subjects. Error for this method was low, in particular when the accelerometer was worn at the lower leg. Asymmetry in hop height was greater in those with higher quadriceps neuromuscular impairment. In Study 3, wearable accelerometers were compared to a system of motion capture cameras and force platform as a method to assess functional movement asymmetry in healthy people and individuals after ACL reconstruction. While walking and stepping down, accelerometers worn at the waist were able to detect underlying movement asymmetry when it exists in people after ACL reconstruction. Acceleration at the waist was strongly associated with vertical ground reaction force and moderately associated with knee extension moments. Collectively, these studies provide evidence that functional movement symmetry can be measured with simple, inexpensive methods that can be used in a variety of clinical or field-based settings.

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