Combined ACL–MCL Injuries: Anatomy, Biomechanics, and Clinical Management

Combined injuries of the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) represent the most frequent pattern of two-ligament knee injury and pose significant diagnostic and therapeutic challenges. While isolated MCL lesions typically respond well to conservative treatment, persistent medial instability in the setting of ACL-MCL injuries has been associated with increased biomechanical stress on the ACL graft and a higher risk of failure. This review synthesizes current anatomical and biomechanical knowledge of the ACL-MCL complex, exploring therapeutic strategies, ranging from non-operative protocols for selected low-grade lesions to advanced surgical reconstructions tailored to injury severity, location, and associated instability patterns.