The anterior cruciate ligament, or ACL, is one of the strongest ligaments about the knee and is an important stabilizer of the joint. It restrains forward sliding of the leg bone (tibia) on the thigh bone (femur). The ACL also helps to control rotation of the femur on the tibia. A ligament such as the ACL, will tear when the force on it exceeds its strength. When a person tears the ACL, the knee frequently becomes painful and swells. The swelling of the knee is usually a result of bleeding of the vessels in the ligament which causes the knee to fill with blood. Limiting motion and applying ice to the knee can help decrease this swelling. When the anterior cruciate tears, it it not uncommon to injure other structures about the knee, such as a meniscus or articular cartilage.
ACL tears usually occur with activities that require that require cutting and pivoting, such as football, skiing, basketball and soccer. Women athletes are more susceptible to tearing their anterior cruciate ligament than men. As we age, our ACL, as well as other ligaments, become weaker and tear with less force. Studies have shown that by the time we are 50 years old, our ACL is 30% as strong as it was when we were 21 years of age.
Anterior cruciate tears may involve the entire ligament or just part of the ligament. If just part of the ligament tears, the remaining fibers may be stretched to the point that the ligament does not function as designed leaving the knee unstable. ACL tears do not heal. Even if the ligament is sewn together after a tear, it will not heal to a functioning structure. To repair a torn ACL requires the ligament to be reconstructed.
Without an anterior cruciate ligament, the knee can “give out” with certain activities, especially running and pivoting. Every time the knee “gives out,” other structures can be damaged. Individuals without functioning anterior cruciate ligaments, can develop early arthritis due to repeated episodes of instability as well as abnormal knee kinematics.
Treatment after an ACL tear depends on numerous factors and should be individualized for each patient. People that are less active and not likely to expose their knee to forces that could cause the joint to “give out,” might do well by strengthening the leg and possibly protecting the joint with a brace during strenuous activity. However, if the person plans on continuing with activity that places stress on the knee, such as sports, than reconstructing the anterior cruciate ligament could be their best option. Most athletes with an unrepaired ACL state their knee feels unstable and they cannot return to their prior activity level. Reconstruction of the anterior cruciate ligament is done using tendons around the person's knee (autograft) or tendons from a deceased person (allograft). Autographs are frequently made from the person's patellar tendon, quadriceps tendon, or one or two of the hamstring (semitendinosis or gracilis) tendons. Allografts can be made from a number of tendons harvested from the donor.