What is anterior cruciate ligament (acl) injury?

The anterior cruciate ligament (ACL) is one of the four ligaments that join the thighbone (femur) to the shinbone (tibia). The ACL helps keep the knee stable. You can tear it when you plant your foot and then push off, change direction, or twist. This can happen during sports like soccer or basketball. Your ACL can also tear when you get hit around your knee. This is more common in a sport like football.

Treatment usually starts with staying off the leg and elevating it, icing the knee, and using a compression bandage.

Your doctor may discuss letting your knee heal with time and physical therapy (PT). You may choose surgery to repair your ACL, especially if you're very active, if other parts of your knee are injured, or if your knee is unstable. Whether you have surgery or not, PT to help you strengthen the muscles around your knee is important.

You'll most likely know it when you have an ACL injury. You may feel or hear a pop. The knee may give out, causing you to fall. The knee swells and often is too painful or unstable for you to keep doing any activity.

An ACL injury can cause partial tears of the ligament or a complete tear (rupture). It can also cause the ligament to separate from the upper or lower leg bone (avulsion). Or it can cause the ligament and part of the bone to separate from the rest of the bone (avulsion fracture). When any of these occur, the lower leg bone moves abnormally forward on the upper bone, with a sense of the knee giving out or buckling.

An ACL injury can lead to long-term knee pain and instability. This is more likely to happen if the injury isn't treated. Treatment to strengthen muscles that support the knee may help.

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.

Treatment for an ACL injury includes using first aid right away. For example, put ice on the knee, prop up the leg, and use over-the-counter pain medicines. You may need to use crutches or a knee immobilizer. You will have exercises and training (rehab) or surgery. If you have surgery, you'll need rehab afterward.

One way to help prevent ACL injuries is to stretch and strengthen the muscles in the legs and body. There are also training programs that teach movements that may prevent injury and help with balance. Warming up before training or competing may also help. Some ACL injuries can happen anyway.

To diagnose an ACL injury, your doctor will ask you to describe how you injured your knee and what you felt. The doctor will check your knee for swelling or tenderness. They may gently push and pull on your leg to see if the knee joint moves in an abnormal way. The exam is usually done on both legs so the doctor can compare one leg to the other to see what's normal for you.

You may have an X-ray to help make sure there isn't a different injury, like a broken bone. Ligaments can't be seen on an X-ray. An MRI is an imaging test that can help show the ACL. It can help your doctor see if you have an ACL tear. Often an injury that causes an ACL tear also injures other ligaments or the cartilage called the meniscus. An MRI can help your doctor diagnose these other injuries.

• 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.

Surgery for an ACL tear can help you stabilize your knee and return to activity. Surgery may include:

• Reconstruction surgery. The surgeon replaces the ACL with tissue called a graft. Usually an autograft is used. For an autograft, the surgeon uses tendon tissue from your own body. This can be done safely. For an allograft, the tendon tissue is from a deceased donor.
• When the damaged ACL pulls a piece of bone off, it is called an avulsion fracture. The surgeon may reconnect the bone fragment to the area it was pulled from.

Things that increase your risk of ACL injuries include:

• Playing sports that involve sudden changes in direction or cutting around other players or obstacles, such as skiing, football, soccer, basketball, baseball, and tennis.
• Having torn your ACL in the past.
• Being female. Females have a higher risk of noncontact ACL tears. These are injuries that did not involve a blow to the knee. For example, if you change direction quickly while your foot is planted.
• Having unbalanced leg muscle strength, such as if the muscles in the front of your thigh (quadriceps) are stronger than the muscles at the back of your thigh (hamstrings).

You can tear your ACL when you plant your foot and then push off, change direction, or pivot. This can happen during certain sports, like soccer or basketball.

You can also tear it from getting hit in your leg or knee during a contact sport like football or in high-speed sports like skiing.

Injuries like those from a car crash, stepping in a hole, or jumping or falling from a height can also cause an ACL tear.

An anterior cruciate ligament (ACL) injury is a tear in one of the knee ligaments that joins the upper leg bone with the lower leg bone. Injuries range from mild, such as a small tear, to severe, such as when the ligament tears completely.

Rehabilitation (rehab) is needed after most ACL injuries, with or without surgery. It'll help you regain normal range of motion and flexibility in your knee. Rehab programs also strengthen the knee and the muscles around it, leading to better knee stability.

Your doctor or physical therapist will design a rehab program for you that considers your normal level of activity, your physical fitness, and the extent of your injury.

A rehab program should include exercises for:

• Flexibility.
• Strength.
• Endurance.
• Coordination and agility training.

How quickly you recover from your ACL injury depends on how severe the injury was, how extensive any surgery was, and how consistent you are to follow the program. The rehab program usually lasts from several months to a year.