Anterior Cruciate Ligament Tears
Introduction
The anterior cruciate ligament (ACL) suffers more injuries than any other ligament in the knee. Injuries to the ACL are often accompanied by collateral ligament tears or a torn meniscus.
If you've hurt your ACL, chances are it happened while playing sports. The number of ACL injuries has grown steadily in recent years, particularly among women. For example, women basketball players are twice as likely as men to suffer an ACL injury. Among soccer players, women are four times more likely to tear an ACL than their male counterparts.
Anatomy
As discussed in the Anatomy section of The Knee Joint, ligaments hold the bones of the knee in place. The "anterior" in ACL means "front," reflecting the fact that the ACL controls the front-to-back motion of the knee joint. It can tear in two ways.
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Causes
The excessive twisting or hyperextension of the knee that typically causes an ACL injury is most likely to happen in contact (football) or pivoting (basketball, skiing, soccer) sports. A football player, for example, might twist his knee running in a zigzag pattern or have it hyperextended during a tackle. In basketball, a player might plant his foot and then quickly change direction, turning his knee too far.
It's unclear why women suffer ACL tears more often than men. Some experts think the female anatomy may leave women more vulnerable. Others say the female hormone estrogen may weaken the ligaments.
Symptoms
Although the symptoms of an ACL tear aren't the same in everyone, there's often a loud "pop" when it happens. After falling to the ground, the victim usually needs help getting up. The knee begins to swell soon after the injury. It may also be unstable, sometimes collapsing or "giving way" when you walk.
Pain and swelling usually last 2 to 4 weeks, but the instability doesn't go away. It's this problem that prompts many people to seek treatment.
Diagnosis
As discussed in the Diagnosis section of Arthritis and other Joint Problems, a history and physical exam will help your doctor make the diagnosis. For example, your doctor will suspect an ACL tear if you tell him your knee swelled soon after the injury. When an ACL ruptures, torn blood vessels often bleed into the knee joint. The blood accumulates quickly, typically causing swelling within 2 hours of the injury. After giving you a local anesthetic, your doctor may insert a needle under your kneecap and drain the fluid. This will relieve swelling and help the doctor confirm the diagnosis. When blood is found in the fluid, a torn ACL is the problem in seven out of 10 cases.
Your doctor can also use other diagnostic tools to confirm an ACL tear. See the sections on X-ray films and MRI scans for more information.
Treatment
To reduce pain and swelling, you'll need to rest for a few days and perhaps use crutches to keep weight off your knee. When using crutches, put your weight on your arms and hands rather than your armpits and bend your elbows. Keep your injured leg off the floor by bending your knee. Move both crutches forward. Then swing your uninjured foot between the crutches, landing heel first.
Once you feel better, you can start exercises to restore range of motion and strengthen knee muscles so they can take over some of the ACL's work of stabilizing the knee. Wearing a special brace should also stabilize your knee.
The need for surgery depends on several factors:
- Age
- Lifestyle
- Other injuries, such as a collateral ligament or meniscal tear
- How much exercises and a brace are helping
- The stability of the knee
The decision to operate is made on a case-by-case basis. For example, a young professional football player who injures his ACL needs surgery to continue his career. A middle-age weekend athlete who tears his ACL playing touch football, on the other hand, may decide not to have surgery.
Repairing an ACL is most often done using arthroscopy. For more on this procedure, see the section on Arthroscopy. Patients often go home shortly after the operation. Occasionally a brief hospital stay is needed.
Using arthroscopy, the surgeon removes the damaged ACL and replaces it with another piece of tissue that will work in the same way the original, uninjured ACL did. In most cases, the doctor uses a bone-patellar tendon-bone graft. He takes about one-third of the patellar tendon (the tendon that connects the kneecap to the lower leg bone) as well as a small piece of bone on either end of the tendon. Using screws, he attaches the piece of bone at one end to the femur and the other to the tibia.
The doctor may also replace the ACL with one or two hamstring tendons from the back of the knee or an allograft (a donated piece of tissue taken from a tissue bank).
To regain motion and strengthen your knee muscles after surgery, your doctor is likely to recommend exercises such as those discussed under Arthroscopy. Gradually, you’ll start walking, jogging, swimming, and biking. Your recovery should take about 6 months and depends on the type of graft you had and the activities you want to resume.
Illustration by: Calhoon, Borman, Mueller
