There are 4 major ligaments in the knee. Ligaments are elastic bands of tissue that connect bones to each other and provide stability and strength to the joint. The four main ligaments in the knee connect the femur (thighbone) to the tibia (shin bone).
The anterior cruciate ligament prevents the femur from sliding backward on the tibia (or the tibia sliding forward on the femur).
The posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backward on the femur).
The medial and lateral collateral ligaments prevent the femur from sliding side to side.
You can injure a ligament through a sharp change in direction, landing wrong from a jump, or the most common a blunt force hit to the knee, such as in football tackle. The incident usually needs to happen at speed. Muscle weakness or incoordination predispose you to a ligament sprain or tear. The anterior cruciate ligament (ACL) is one of the most common ligaments to be injured. The ACL is often stretched and/or torn during a sudden twisting motion (when the feet stay planted one way, but the knees turn the other way). Skiing, basketball, and football are sports that have a higher risk of ACL injuries. The posterior cruciate ligament (PCL) is also a common ligament to become injured in the knee. However, the PCL injury usually occurs with sudden, direct impact, such as in a car accident or during a football tackle. The medial collateral ligament is injured more often than the lateral collateral ligament. Stretch and tear injuries to the collateral ligaments are usually caused by a blow to the outer side of the knee, such as when playing hockey or football.