Anatomy: The ACL is one of the four main stabilizing ligaments in the knee joint. The others include the posterior cruciate ligament (PCL), medial collateral ligament (MCL) and lateral collateral ligament (LCL). The PCL works with the ACL. It prevents the tibia from sliding backwards under the femur. The MCL runs along the inner part (side) of the knee and prevents the knee from bending inward. The LCL runs along the outer part of the knee and prevents the knee from bending outward. The ACL attaches to the femur at the back of the joint and passes down through the knee joint to the front of the flat upper surface of the tibia. It passes across the knee joint in a diagonal direction and the PCL passes it in the opposite direction, forming a crossing pattern between the two, hence the name cruciate ligaments. The role of the ACL is to prevent forward movement of the tibia from underneath the femur. The PCL prevents movement of the tibia in a backwards direction. Together these ligaments are extremely important for the stability of the knee joint, especially in contact sports and those that involve fast cutting and changing directions quickly, twisting and pivoting. By definition, a knee sprain is an injury to a knee ligament. A sprain is a joint injury that causes a stretch or a tear in a ligament, and ligaments function to connect bone to bone. The ACL connects the thigh bone to the shin bone. ACL sprains are graded I, II, or III depending on their severity: grade I sprain: pain with minimal damage to the ligaments, grade II sprain: more ligament damage and mild looseness of the joint, grade III sprain: the ligament is completely torn and the joint is very loose or unstable.
Causes of Injury: ACL sprains may be due to contact or non-contact injuries. A blow to the side of the knee, which can occur during a football tackle, may result in an ACL sprain or tear. Coming to a quick stop, combined with a change in direction while running, pivoting,