ACL (Anterior Cruciate Ligament) Injuries
Key points
- Ligaments are tough bands of fibrous tissue that connect two bones, providing stability.
- In diagnosing an ACL sprain, your doctor will want to know exactly how you hurt your knee.
- How long you have problems depends on the severity of your injury, your rehabilitation program and the types of sports you play.
- Your doctor also may suggest that you wear a knee brace, and that you take a nonsteroidal anti-inflammatory drug, such as ibuprofen (Advil, Motrin and others), to relieve pain and ease swelling.
What Is It?
Ligaments are tough bands of fibrous tissue that connect two bones, providing stability. 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, which is a tear of a ligament. In almost all cases, the ACL is torn during at least one of the following patterns of injury:
- A sudden stop, twist, pivot or change in direction at the knee joint — These knee movements are a routine part of football, basketball, soccer, rugby, gymnastics and skiing. For this reason, athletes who participate in these sports have an especially high risk of ACL tears.
- Extreme hyperextension of the knee — Sometimes, during athletic jumps and landings, the knee straightens out more than it should and extends beyond its normal range of motion, causing an ACL tear. This type of ACL injury often occurs because of a missed dismount in gymnastics or an awkward landing in basketball.
- Direct contact — The ACL may be injured during contact sports, usually as the result of a direct impact to the outside of the knee or lower leg. Examples are a sideways football tackle, a misdirected soccer kick that strikes the knee or a sliding tackle in soccer.
Like other types of sprains, ACL injuries are classified by the following grading system:
- Grade I — A mild injury that causes only microscopic tears in the ACL. Although these tiny tears may stretch the ligament out of shape, they do not affect the overall ability of the knee joint to support your weight.
- Grade II — A moderate injury in which the ACL is partially torn. The knee can be somewhat unstable and can "give way" periodically when you stand or walk.
- Grade III — A severe injury in which the ACL is completely torn through and the knee feels very unstable.
Overall, most ACL injuries are severe Grade IIIs, with only 10 percent to 28 percent 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 percent 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.
Written and revised by
David Cohen, M.D.
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