Anterior cruciate ligament

The anterior cruciate ligament (ACL) is a ligament inside the knee that connects the femur to the tibia. It restrains forward movement and rotation of the tibia, helping stabilize the joint.

Knee joint: The synovial joint between the femur, tibia, and patella that enables movement of the leg. The ACL is one stabilizer within this joint’s complex, moving structure.
Anterior cruciate ligament injury: Damage to the ACL, ranging from a sprain to a complete tear. Injury interrupts the restraints this ligament normally provides.
Medial collateral ligament: A ligament on the inner side of the knee that resists forces pushing the knee inward. Unlike the ACL, it lies outside the joint and primarily resists valgus stress.
Noncontact ACL injury: An ACL injury occurring without direct impact to the knee, often during abrupt deceleration or direction change. This frequent injury pattern reflects loading during cutting, landing, or sudden stopping.
Posterior cruciate ligament: A ligament inside the knee that connects the femur and tibia and restrains backward movement of the tibia. It crosses the ACL and resists tibial motion in the opposite direction.
Lachman test: A physical examination maneuver that assesses anterior translation of the tibia with the knee slightly flexed. Excessive translation can indicate ACL insufficiency.
Posterolateral corner injury: Damage to structures on the outer-back side of the knee that resist rotational and varus forces. It can cause instability resembling ACL deficiency but involves a different restraint system.
ACL injury in alpine skiing: An ACL injury sustained during alpine skiing, often through falls or twisting forces on the knee. Skiing exposes the ligament to distinctive combinations of rotation and external force.
Meniscus: A crescent-shaped fibrocartilage structure that distributes load and improves fit between the femur and tibia. Meniscal support works alongside ligament restraints to stabilize the knee.
Pivot-shift test: A clinical maneuver that elicits rotational instability associated with ACL deficiency. It tests a functional consequence of losing ACL control of tibial rotation.

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Human legBroader topic: It is commonly injured during pivoting sports that load the knee.