The anterior cruciate ligament (ACL) is a commonly injured ligament in the knee. Ligaments are tough bands of tissue that connect the ends of bones together.
The ACL is located in the center of the knee joint, where it runs from the backside of the femur (thigh bone) to connect to the front of the tibia (shin bone). It has two main functions:
The ACL plays an especially important role when performing activities that require quickly changing direction, such as soccer, football and basketball. If the knee receives too much stress, the ACL could be strained or completely torn.
Athletes who tear their ACL sometimes report a sensation of their knee "giving out." Short term, this makes it difficult to play sports. Long term, it is believed that this "giving out" causes damage to other structures in the knee, including the cartilage, which can cause arthritis.
Anyone can suffer an ACL injury; however, proper training can help athletes minimize their risk. Females are approximately six times more likely to tear their ACL than males, due to reasons ranging from differences in bone structure to muscle imbalances.
Research has shown that about one in every 60 young athletes will experience an ACL tear at some point during their athletic career. Unfortunately, these numbers are increasing due to the increased intensity of sports.
Impact to the outside of the knee or sudden changes in direction can stretch, fray or tear the ACL completely. Too much strain on the knee joint from sharp pivots or quick stops can also injure the ACL. An ACL injury can also occur without any contact.
Prevention starts with understanding the importance of balancing the strength of the muscles around your knee and core. The ACL is at highest risk when the hamstrings do not fire with enough force or at the right timing to protect the ACL. Good muscle strength and coordination minimizes injuries - this includes strength in your hamstrings, quadriceps and your core (abdominal and gluteal muscles).
Many anterior cruciate ligament (ACL) injuries happen while playing sports, but not necessarily from a hard collision. In fact, most ACL injuries are what we call "non-contact," meaning they occur during a sudden change in direction, not when struck by another player.
Outside of traditional sports, ACL injuries can occur whenever someone is doing something active - at a playground, riding a bike or playing tag. ACL tears are also often caused by from car accidents or other traumatic events.
Athletes who have suffered an ACL injury typically experience rapid swelling of the knee within 24 hours of the injury. Some may be able to walk after the injury, or even continue to play their sport. Many people report that they hear or feel a "pop" in their knee when the injury occurs. As the swelling subsides over the following days or weeks, most people notice that their knee feels unstable or "gives out."