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ACL Injuries

What is an anterior cruciate ligament (ACL) injury?

An anterior cruciate ligament, or ACL, injury is a tear in one of the knee ligaments that joins the upper leg bone with the lower leg bone. The ACL keeps the knee stable.

Injuries range from mild, such as a small tear, to severe, such as when the ligament tears completely or when the ligament and part of the bone separate from the rest of the bone.

Without treatment, the injured ACL is less able to control knee movement, and the bones are more likely to rub against each other. This is called chronic ACL deficiency. The abnormal bone movement can also damage the tissue (cartilage) that covers the ends of the bones. And it can trap and tear the pads (menisci) that cushion the knee joints. This damage can lead to osteoarthritis.

  • Symptoms

    What are the symptoms of an anterior cruciate ligament (ACL) injury?

    Symptoms of a severe and sudden (acute) ACL injury include:

    • Feeling or hearing a pop in the knee at the time of injury.
    • Pain on the outside and back of the knee.
    • The knee swelling within the first few hours of the injury. This may be a sign of bleeding inside the knee joint. Swelling that occurs suddenly is usually a sign of a serious knee injury.
    • Limited knee movement because of pain or swelling or both.
    • The knee feeling unstable, buckling, or giving out.

    After an acute injury, you will probably have to stop whatever you are doing because of the pain. But you may be able to walk.

    The main symptom of chronic (long-lasting and recurrent) ACL deficiency is the knee buckling or giving out, sometimes with pain and swelling. This can happen when an ACL injury isn't treated.

  • Causes

    What causes an anterior cruciate ligament (ACL) injury?

    You can injure your ACL if your knee joint is bent backward, twisted, or bent from side to side. The chance of injury is higher if you do more than one of these movements at the same time. Contact with (being hit by) another person or object also can cause an ACL injury.

    An ACL injury often occurs during sports. The injury can happen when your foot is firmly planted on the ground and a sudden force hits your knee while your leg is straight or slightly bent. This can happen when you change direction quickly, slow down while running, or land from a jump. This type of injury is common in soccer, skiing, football, and other sports with lots of stop-and-go movements, jumping, or weaving.

    Falling off a ladder or missing a step on a staircase are other likely causes.

    This type of injury happens more easily in people older than age 40.

  • Pevention

    Preventing an anterior cruciate ligament (ACL) injury

    A lot of the research on preventing ACL injuries has focused on women: women athletes injure their ACLs up to 8 times as often as men athletes. Although the following tips come from women's programs, they can help anyone prevent ACL injuries.

    • Warm up.

      Always warm up before training or competition. Ways to warm up include jogging easily or riding a stationary bicycle for 5 to 10 minutes. Warming up your muscles reduces the risk of injury.

    • Stretch.

      Make stretching part of your warm-up before the activity and your cool-down after the activity. Stretching can help you keep and improve your range of motion and reduce stiffness in your joints. It may also reduce soreness after exercise and reduce the risk of injury.

    • Practice landing skills.

      This is more important for women, because they don't usually bend their knees as much as men do when landing from a jump. Not bending the knees enough exposes them to more pressure and increases the risk for an ACL injury. When landing after jumping:

      • Land with the knees bent. As the knees bend during landing, make sure they travel in a straight path. Do not let them move closer together.
      • Land softly on the balls of the feet and roll back onto the heels.
      • Keep your knees and hips aligned and your upper body upright. Don't bend too far forward or backward as you land.
      • Try not to land on one foot. If this is not possible, bring the other foot down as soon as possible to spread your weight evenly.
    • Improve agility.

      Women tend to turn and pivot in a more erect position than men, which strains the ACL. Learning to crouch and bend at the knees and hips when turning may reduce the stress on the ACL. Agility exercises include running forward and backward and running in diagonals. (You run diagonally to one spot, then cut the other way and run to another.)

    • Work on muscle strength.

      The muscles in the back (hamstrings) and front (quadriceps) of the thighs work together to bend or straighten the leg. Women tend to use their quadriceps when changing direction quickly. This can result in an ACL injury. You can stretch and strengthen the quadriceps and hamstrings to help reduce the risk.

  • Diagnosis

    How is an anterior cruciate ligament (ACL) injury diagnosed?

    Your doctor can tell if you have an ACL injury by asking questions about your past health and checking your knee. The doctor may ask: How did you injure your knee? Have you had any other knee injuries?

    Your doctor will check for stability, strength, range of movement, swelling, and tenderness in both the injured knee and uninjured knee. You may need tests for stability, such as a Lachman test and a pivot shift test. The Lachman test compares the degree of looseness in your knees.

    You may need X-rays. X-rays can show damage to the knee bones. Or you may need other imaging tests, like an MRI. An MRI can show damage to ligaments, tendons, muscles, and knee cartilage. A procedure called arthroscopy may also be done. During arthroscopy, your doctor inserts a tiny camera through one or more small cuts (incisions) in the knee to look at the inside of the knee.

  • Treatment

    How is an anterior cruciate ligament (ACL) injury treated?

    Treatment for an ACL injury includes:

    • First aid right away.
      • Reduce swelling and pain. To do this, you may rest the knee, apply ice, wrap your knee gently with an elastic bandage, and prop up (elevate) the leg.
      • Move your leg as little as you can.
      • Take over-the-counter pain medicine, such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs).
    • Crutches and a knee immobilizer. These help keep your knee still for the first few days after the injury. But if they're used for too long, the muscles will get weaker from too little activity.
    • Exercises and training, also called rehab. It takes several months of rehab for your knee to get better.
    • Surgery. You and your doctor can decide if rehab is enough or if surgery is right for you. If you have surgery, you will also have several months of rehab afterward.
  • Self-care

    How can you care for yourself when you have an anterior cruciate ligament (ACL) injury?

    • Follow your doctor’s directions for wearing a brace or an immobilizer, which limits movement of your knee. Wrapping your knee with an elastic bandage may help reduce or prevent swelling.
    • Use crutches as directed in the first few days after your injury if your doctor recommends them.
    • Rest your knee when possible. But try to flex your calf muscles often to help blood circulate in your legs.
    • Put ice or a cold pack on your knee for 10 to 20 minutes at a time. Try to do this every 1 to 2 hours during the next 3 days (when you are awake) or until the swelling goes down. Put a thin cloth between the ice and your skin.
    • Prop up your leg on a pillow when you ice it or anytime you sit or lie down during the next 3 days. Try to keep it above the level of your heart. This will help reduce swelling.
    • Take pain medicines exactly as directed.
      • If the doctor gave you a prescription medicine for pain, take it as prescribed.
      • If you are not taking a prescription pain medicine, take an over-the-counter medicine to reduce pain and swelling. These include ibuprofen (Advil, Motrin) and naproxen (Aleve). Read and follow all instructions on the label.
    • Follow your doctor’s or physical therapist’s directions for strength exercises. Exercises to make your thigh muscles stronger and increase knee motion can help you get ready for a physical rehabilitation (rehab) program or surgery with a rehab program. Here are a few exercises you can do if your doctor says it is okay.
      • Quad sets: Lie down on the floor or the bed with your injured leg straight. Fully extend your leg—there should be no or little bend in your knee. Tighten the thigh (quadriceps) of your injured leg for 10 seconds. Do not lift your heel up. Relax your quadriceps for 10 seconds. Repeat 8 to 12 times several times during the day.
      • Straight-leg raises: Lie down on the floor or the bed with your injured leg flat and your uninjured leg bent so that the bottom of your foot is on the floor or bed. Tighten the quadriceps of your injured leg. Keeping your knee as straight as possible, lift your injured leg off the bed until it is about 18 inches above the bed or floor. Lower your leg back down and relax for 5 seconds. Do 3 sets of 8 to 12 repetitions.
      • Heel slides: Lie down on the floor or the bed with your leg flat. Slowly begin to slide your heel toward your rear end (buttocks), keeping your heel on the floor. Your knee will begin to bend. Slide your heel and bend your knee until it becomes a little sore and you can feel a small amount of pressure inside your knee. Hold this position for 15 to 30 seconds. Slide your heel back down until your leg is straight on the floor. Relax for 10 seconds. Repeat 2 to 4 times several times during the day.
      • Side-lying leg lifts: Lie on your side with your legs straight and the injured leg on top. Keeping your leg straight, raise your injured leg up and backward about 6 inches. Lower the leg to the starting position. Do 3 sets of 20 repetitions, or if you tire quickly, 3 sets of 8 to 12 repetitions.

    Copyrighted material adapted with permission from Healthwise, Incorporated. This information does not replace the advice of a doctor.