ACL repair surgery refers to a surgical procedure performed to address a torn anterior cruciate ligament (ACL) in the knee. The ACL is one of the major ligaments in the knee, and its primary function is to stabilize the joint by preventing excessive forward movement of the tibia (shinbone) relative to the femur (thighbone). Injuries to the ACL are common, especially among athletes involved in sports that require sudden stops, changes in direction, or jumping.