What is the ACL?
The Anterior Cruciate Ligament (ACL) is a very strong ligament in the center of the knee. It's function is to prevent the lower leg, or tibia, from sliding forward on the thigh bone, or femur. The ACL attaches on the femur in a tight boney notch. The roof of this notch can shear off the ligament in an injury, tearing the ligament. Females in general have a tighter notch, leading to seven more times the rate of ACL tears compared to males.

How is the ACL injured?
The ACL is torn when the lower leg is driven forward on the thigh bone. This often occurs when a person attempts to plant his/her foot and cut to the side while running. A similar twisting injury occurs with skiing, or when coming down from a jump in sports such as volleyball or basketball. Contact injuries in football or soccer are also common mechanisms. Unfortunately, the collateral ligaments on either side of the knee, and the meniscus cartilages inside the knee, are frequently torn at the same time.

What is the problem?
Athletes with a torn ACL may experience giving way of the knee when they attempt running, jumping, or twisting sports. With each giving way episode, they may further injure other structures inside the knee. An athlete with an unstable knee therefore has two basic choices: avoid sports that involve running, jumping, or twisting, or have surgical reconstruction. Braces sometimes help, but they are not strong enough to prevent giving way episodes in an unstable knee.

Do I need surgery?
Not all knees with ACL tears are functionally unstable. That is, some people's knees are not as loose as others with similar injuries, and their knees do not give way with the activities they want to continue. These individuals probable do not need surgery. They can maintain optimal thigh muscle strength (especially the quadriceps) through a non-impact program such as bicycling, and do very well. However, if a person is unwilling to give up running, jumping, or twisting sports, and has an unstable knee, then surgery is recommended; especially for younger patients with many years of athletics ahead. Also, people who experience giving way with daily activities, even if not involved in sports, may need surgery to avoid further knee injury.

Surgery
Reconstruction of the ACL involves using a graft (a substitute ligament) from another part of the knee like the patella tendon or hamstring tendons. The graft is placed within bone tunnels drilled in the femur and tibia, then fixed with metal screws on either end of the position of the original ACL. Surgery takes between one and two hours and is largely done athroscopically. The arthroscope is roughly the size of a pencil and allows the surgeon to see inside the knee on a TV monitor. Patients may spend one night in the hospital. Rehabilitation takes an average six months to completely regain muscle strength. At that point, an athlete may resume any sport he chooses. In fact, many professional athletes have had their ACL reconstructed to return to productive careers, usually without need of a brace.