Anterior Cruciate Ligament (ACL) Injury Mechanisms in Men's Major League Soccer: A Systematic Video Analysis

Introduction Anterior cruciate ligament (ACL) injuries are common in professional soccer; however, limited research has described the situational mechanisms of injury in men's major league soccer (MLS) in the United States and Canada. Understanding these mechanisms is essential for developing targeted prevention and rehabilitation strategies. Objective This study aims to identify situational patterns and positional characteristics associated with ACL injuries in MLS players. Methods Across five and a half MLS seasons, 65 ACL injuries were identified. Video footage was available for 33 injuries, which were analyzed to determine the mechanism of injury, player activity at the time of injury, knee position, and external factors, including field type, month of injury, and timing within the game. Results Non-contact injuries were most common (64%), followed by direct (21%) and indirect-contact (15%) injuries. Injuries most frequently occurred during defensive pressing (76%) and offensive driving (58%). Knee valgus (82%) and flexion (85%) were the predominant positions at the time of injury. All indirect-contact injuries involved force applied to the upper body, increasing stress on the knee. Injuries occurred more commonly on grass fields during the second half or overtime (61%) and demonstrated a bimodal distribution across the season. Overall, 79% of ACL injuries occurred without direct contact to the affected knee. Conclusion ACL injuries in MLS primarily result from non-contact or indirect-contact mechanisms, often during pressing or driving movements, with the knee loaded in valgus and flexion. These findings can inform sport-specific prevention strategies aimed at reducing ACL injury risk and prolonging athlete participation in professional soccer.