Anterior Cruciate Ligament (ACL) Injuries
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Anterior Cruciate Ligament (ACL) Injuries

What Are ACL Injuries?

A torn anterior cruciate ligament (ACL) is a serious knee injury, especially for athletes. Ligaments are long, rope-like bands that fasten bones together. The ACL helps give the knee its stability.

How Do ACL Injuries Happen?

Teens who get ACL injuries usually play contact sports (like football) or sports that feature swift, abrupt movements such as pivoting, stopping, or turning on a dime.

People also can tear an ACL when they do movements they're used to doing all the time, like jumping and landing hard on the feet. If the quadriceps muscles aren't strong enough, a movement a player is used to doing can suddenly put too much pressure on the knee joint and cause the ACL to tear or break apart.

Teen girls are much more likely than guys to tear an ACL. There are several reasons why, including the fact that girls and guys have different body shapes and limb alignment. Hormones can play a role too. Female hormones may loosen the ligaments.

ACL injuries can really hurt. They can also lead people to be unsteady on their feet during sports. Depending on the person's age and the severity of the injury, a torn ACL usually heals best with surgery in addition to 6 to 12 months of rehabilitation. Getting surgery can prevent a player from getting arthritis or other knee damage later on.

What Are the Signs of an ACL Injury?

Here's what most people notice after tearing an ACL:

  • pain, which may be intense
  • inability to put weight on the affected leg
  • swelling in the knee joint within 24 hours of the tear

Many people report hearing a "pop" sound when the injury happens. This is the sound of the shinbone popping out and back into place when the ligament tears. Others also report the knee feeling looser than it was before. Sometimes, though, people with ACL injuries don't notice anything different. It all depends on how severe the injury is.

If you injure your knee — whether out on the field or at home — stop all activity to prevent further injury. See a doctor as soon as possible. In the meantime, keep your knee iced and elevated to reduce swelling. If it feels painful, don't put weight on your knee.

How Are ACL Injuries Diagnosed?

A doctor will examine the knee and probably do imaging tests to see how it might be injured and, if so, how badly.

These tests can help diagnose an ACL injury:

  • Lachman test. During this exam, a person will lie down flat on his or her back with the affected knee lifted and flexed at a 20- to 30-degree angle. The doctor then places one hand on the person's calf and the other on the top of the thigh, applying pressure to move the shin forward. If it moves too far forward, it can signal a torn ACL.
  • Anterior drawer test. During this test, the hip is flexed at 45 degrees and the knee at 90 degrees. The examiner grasps the back of the shin, just below the knee, placing index fingers on hamstring tendons and thumbs on the side of the kneecaps to feel any shift of the knee joint and surrounding areas while attempting to pull the tibia forward.

Doctors may order X-rays with knee injuries, but that's usually to see if a bone is fractured, since X-rays only image bone. So some doctors will order an MRI, which images tissue (like ligaments and muscles), to confirm a partial or complete ACL tear.

How Are ACL Injuries Treated?

Doctors highly recommend surgery for teens with ACL injuries.

A torn ACL usually is treated with a procedure called an ACL reconstruction. Surgeons replace the damaged ligament with new ACL graft tissue — either taken from the patient's own body (tissue from the main patellar tendon or the hamstring) or donated from someone else (called an allograft).

What Is Recovery Like?

After surgery, patients will need to use crutches, limit physical activity, and wear a knee brace for a while, depending on what the surgeon advises.

Recovery from ACL surgery can take 6 months to a year. Rehabilitation ("rehab") therapy is needed to help heal the knee and to:

  • restore range of motion
  • regain strength in the knee, thigh, and shin muscles
  • prevent atrophy (the breakdown of muscle tissue)
  • reduce pain and swelling
  • improve balance

Most people do rehab at a center three times a week, with daily exercises they practice at home. Accelerated rehab programs involve more frequent therapy, but they won't necessarily speed recovery.

In the early stages of recovery, a doctor may recommend a leg brace or knee brace. Keeping the knee iced and raised can help to reduce swelling. Doctors usually prescribe painkillers and anti-inflammatory medicine to help you deal with the pain and feel more comfortable. In some cases, doctors may give you steroid injections to ease pain and help reduce swelling.

While most sports are off limits — especially the activity that caused the injury in the first place — you might try some low-impact activities like swimming, bike riding, or protected running. Talk to your doctor about what activities might help you; some of these may even count as therapies.

Looking Ahead

Being told that you can't do the things you love — like running or playing football, field hockey, or softball — can be frustrating. Recovering from an ACL injury might make you feel angry or even depressed, especially if you're no longer playing team sports with your friends.

But in the meantime, there are ways to still feel like part of the team. Keeping score, being a coach's assistant, or bringing water to your teammates may help. If you don't want to do these, start something new, like playing the guitar, painting, drawing, or another activity that won't put strain on the knee.

In time, you can do the things you love. If you feel like you're struggling with recovery, consider talking to a counselor for support.

Date reviewed: October 2015