The anterior cruciate ligament (ACL) is one of the bands of tissue that connects the femur, or thigh bone, to the tibia, or shin bone, in your knee joint. The ACL crosses the posterior cruciate ligament (PCL) to form an X. Together, these ligaments control the back-and-forth motion of your knee.

When your knee experiences a great force or more stress than it can bear, an ACL tear or sprain may result.