Effect of previous hamstring strain on Anterior Cruciate Ligament (ACL) forces

Introduction: Anterior Cruciate Ligament (ACL) injuries are very common in the athletic population. While the hamstring muscles help protect the ACL, hamstring strain injuries (HSI) are also common in sports. After HSI, the muscle goes through many different adaptations that often alter the overall function of the hamstrings. Therefore, it is possible that the associated deficits to hamstring muscle function after HSI may alter ACL loading. Methods: Nine subjects were included in the study. Six in the healthy control group, and three in the previous HSI group. We used an ultrasound based subject-specific musculoskeletal model to estimate muscle forces and ACL forces during walking, squatting, and landing from a jump. Ultrasound data, along with static calibration from motion capture, were used to develop the subject specific model. The purpose of this study was to determine if people with a previous hamstring strain had increased ACL forces during common activities of daily living and sport compared to healthy controls. We hypothesize that people who have had a previous hamstring strain injury will have increased forces on the anterior cruciate ligament compared to individuals with no history of hamstring injury. Results: Our results did not support our hypothesis. People with a previous HSI did not have increased ACL forces compared to healthy controls. Discussion: Three subjects in the previous HSI group move differently compared to the control group. In three of the four dynamic tasks, the previous HSI subjects demonstrated significantly less sagittal plane hip range of motion compared to healthy controls. We also found significant differences in hamstring EMG during the drop jump task. We concluded that people may move differently after sustaining a HSI to compensate and ultimately decrease their risk of further injury