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Sports fans across the country cringe when they hear about an ACL (Anterior Cruciate Ligament) tear. Many a professional athlete's season has come to an abrupt end thanks to this very common injury.

The anterior cruciate ligament (ACL) is a very important stabilizer of the knee. There are approximately 100,000 to 200,000 ACL ruptures per year in the United States alone. These injuries are common in professional and recreational athletes across multiple different sports.

While ACL tears are common, many questions surround the injury and available treatment. Here are some answers.

What is the ACL and what is its main function?

A ligament is a tough band of tissue that connects one bone to another. The ACL connects the thigh bone (femur) to the shin bone (tibia). It prevents these bones from extending beyond a normal angle and guards against over rotation.

What is the mechanism of an ACL tear?

The ACL can tear with both contact and noncontact maneuvers. Approximately 70 percent of injuries are noncontact and occur when the athlete is trying to change directions, slow down or land from a jump. In contact injuries, a direct blow can cause the knee to hyperextend or bend inward (valgus stress).

Are female athletes more likely to sustain an ACL tear than male athletes?

Yes. Orthopedic studies confirm that female athletes at two to 10 times greater risk than males depending on the sport.  In soccer, females are three to five times more likely to sustain an ACL tear. Among basketball players, females are at two to seven times greater risk.

What are the signs and symptoms of an ACL tear?

An audible "pop" is heard approximately 70 percent of the time. Athletes commonly say they felt one or more "pops" or "cracks." Swelling occurs within a few hours and nearly all patients develop bleeding into their knee joint (hemarthrosis). The person is unable to return to play due to pain and instability. After the swelling subsides, patients generally are able to bear weight on the injured leg, but complain of instability.

What do you do if you think you tore your ACL?

After sustaining the injury the athlete should be removed from the field of play. An ace wrap, ice and a knee immobilizer, if available, should be applied. Crutches should be used. An evaluation in the emergency room is advisable to obtain x-rays, have an exam performed and possibly to remove the blood from the knee to help with the pain.  If there is any question of a possible ACL tear, then a referral to a sports medicine orthopedist is necessary.

Is there a test that can be done to check for an ACL tear?

Yes. The best test is called the Lachman Test, which checks displacement of the tibia on the femur with the knee flexed 30 degrees. The physician also will determine if there is a solid, soft or no end-point of the ligament when doing the test. There are other tests as well that can be done when the swelling subsides called the Anterior Drawer Test and the Pivot Shift Test. MRI scans are routinely done, not only to confirm the diagnosis, but to rule out other injuries of the knee.

Does everyone need surgery?

No. Older, less active patients can do well without reconstruction if they participate in rehabilitation and modify their activities. The goal is to return the function of the quadriceps and hamstring muscles to within 90 percent of the other leg. People who also have moderate or severe arthritis are not good candidates for an ACL reconstruction.  Athletically active patients who wish to continue to participate in running, cutting, jumping and pivoting sports are excellent candidates for an ACL reconstruction.

Can the ACL be repaired?

ACL reconstruction (different from "ACL repair") was developed due to high historical failure rates for ACL repairs. No longer the treatment of choice, ACL repairs in the past involved reattaching the ligament to the bone with staples or other devices. 

How is an ACL reconstruction performed?

Most ACL reconstructions are now performed all-arthroscopically or arthroscopically-assisted with a small incision of about 3 cm. In these minimally invasive techniques, a graft (piece of tendon) is placed into the knee to replace the torn ACL. The grafts are secured into sockets created in the thigh bone (femur) and shin bone (tibia) in very precise positions.  The grafts can be secured with many different types of metal, plastic or bioabsorbable implants to allow for aggressive postoperative rehabilitation.

Do you have to participate in physical therapy after an ACL reconstruction?

Yes. There are now advanced physical therapy protocols that allow the patients to increase their range of motion, decrease swelling and pain and regain control and strength of their muscles more quickly. There are fewer complications when patients participate in a rehabilitation program compared to doing the exercises on their own. Physical therapy generally starts two days after surgery and lasts three to four months.

What are the outcomes after an ACL reconstruction?

When performed with careful surgical technique and appropriate rehabilitation, the outcome is successful  more than 90 percent of the time. The re-tear rates are usually less than 5 percent in most studies. A return to sports usually takes four to six months.

Can ACL injuries be prevented?

Yes. There are many different programs that are being used to help athletes decrease their chances of an ACL tear. The programs focus on exercises that make the muscles surrounding the knee strong and flexible. These programs also include increasing core strength as well as practicing positioning of the limbs when jumping. For more information on these programs, talk to your athletic trainer or primary care physician.