What Is It?
Ligaments are tough bands of fibrous tissue that connect two bones. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are inside the knee joint. These ligaments connect the thigh bone (femur) and the large bone of the lower leg (tibia) at the knee joint. The ACL and PCL form an "X" inside the knee that stabilizes the knee against front-to-back or back-to-front forces.
An ACL injury is a sprain, in which the ligament is torn or stretched beyond its normal range. In almost all cases, when the ACL is torn, it's almost always due to at least one of the following patterns of injury:
Like other types of sprains, ACL injuries are classified by the following grading system:
Overall, most ACL injuries are severe Grade IIIs, with only 10% to 28% being either Grade I or Grade II. Currently, between 100,000 and 250,000 ACL injuries occur each year in the United States, affecting approximately one out of every 3,000 Americans. Although most of these injuries are related to athletic activities, especially contact sports, about 75% occur without any direct contact with another player.
Women who play contact sports injure their ACLs about seven times more often than men who play such sports. So far, sports medicine experts have not been able to determine why women athletes have a higher risk of ACL injuries. Some researchers believe it's related to a slight difference in the anatomy of the knee in males and females. Others blame it on the effects of female hormones on body ligaments. Still others point to differences between females and males in skill, training, conditioning or even athletic shoes.
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