Anterior Cruciate Ligament (ACL) Injury

What is an anterior cruciate ligament (ACL) injury?

The anterior cruciate ligament (ACL) is one of the major ligaments in the middle of the knee. Ligaments are strong bands of tissue that connect one bone to another. The ACL connects the thighbone (femur) to the shin bone (tibia). This ligament, along with the posterior cruciate ligament, helps keep the knee stable and protects the femur from sliding or turning on the tibia. A sprain is a joint injury that causes a stretch or a tear in a ligament.

Sprains are graded 1, 2, or 3 depending on their severity:

• grade 1 sprain: pain with minimal damage to the ligaments
• grade 2 sprain: more ligament damage and mild looseness of the joint
• grade 3 sprain: the ligament is completely torn and the joint is very loose or unstable

The ACL may be completely torn or partially torn. Most injuries are complete tears.

How does it occur?

The anterior cruciate ligament is frequently injured in forced twisting motions of the knee. It may also become injured when the knee is straightened further than it normally can straighten (hyperextended). It sometimes happens when the thigh bone is forcefully pushed across the shin bone, such as with a sudden stop while you are running or a sudden transfer of weight while you are skiing.

What are the symptoms?

There is usually a loud, painful pop when the joint is first injured. This is often followed by a lot of swelling of the knee within the first several hours after the injury. This swelling is called an effusion and is made up of blood in the knee joint. You may find it hard to fully bend or straighten your knee.

If you tore your anterior cruciate ligament months or years ago and you haven't had reconstructive surgery, you may have the feeling that the knee is giving way during twisting or turning movements.

How is it diagnosed?

Your healthcare provider will examine your knee and may find that your knee has become loose. If you have swelling in the joint, he or she may decide to remove the blood in your knee with a needle and syringe. You may need X-rays to see if there is an injury to the bones in your knee. An MRI (magnetic resonance imaging) scan may also be done and should clearly show the condition of your ACL (as well as that of other ligaments and cartilage).

How is it treated?

To treat this condition:

• Put an ice pack, gel pack, or package of frozen vegetables, wrapped in a cloth on the area every 3 to 4 hours, for up to 20 minutes at a time.
• Raise the knee on a pillow when you sit or lie down.
• Take an anti-inflammatory medicine such as ibuprofen, or other medicine as directed by your provider. Nonsteroidal anti-inflammatory medicines (NSAIDs) may cause stomach bleeding and other problems. These risks increase with age. Read the label and take as directed. Unless recommended by your healthcare provider, do not take for more than 10 days.
• Follow your provider’s instructions for doing exercises to help you recover.

Your provider may recommend that you:

• Wrap an elastic bandage around your knee to keep the swelling from getting worse.
• Use a knee immobilizer initially to protect the knee.
• Use crutches.

For complete tears, you and your healthcare provider will decide if you should have intense rehabilitation or if you should have surgery followed by rehabilitation. The torn anterior cruciate ligament cannot be sewn back together. The ligament must be reconstructed by taking ligaments or tendons from another part of your leg and connecting them to the tibia and femur.

You may consider having reconstructive ACL surgery if:

• Your knee is unstable and gives out during routine or athletic activity.
• You are a high-level athlete and your knee could be unstable and give out during your sport (for example, basketball, football, or soccer).
• You are not willing to give up an athletic lifestyle.
• You want to prevent further injury to your knee. An unstable knee may lead to injuries and arthritis.

If you can do your normal activities without pain and are willing to give up playing sports that put extra stress on the knee, you may not need surgery. If a growing child tears an ACL, the healthcare provider may recommend that surgery be postponed until the child has stopped growing.

How long will the effects last?

When you tear your ACL you will have pain and swelling for several weeks. You need to stop doing the activities that cause pain. If you continue doing activities that cause pain, your symptoms will continue.

If you have a completely torn anterior cruciate ligament the effects will be chronic. Your knee may feel loose and feel like it will give way when you are running and making quick turns. Rehabilitation exercises and a special brace will help improve these symptoms.

When can I return to my normal activities?

Everyone recovers from an injury at a different rate. Return to your activities depends on how soon your knee recovers, not by how many days or weeks it has been since your injury has occurred. In general, the longer you have symptoms before you start treatment, the longer it will take to get better. The goal of rehabilitation is to return you to your normal activities as soon as is safely possible. If you return too soon you may worsen your injury.

You may safely return to your normal activities when, starting from the top of the list and progressing to the end, each of the following is true:

• Your injured knee can be fully straightened and bent without pain.
• Your knee and leg have regained normal strength compared to the uninjured knee and leg.
• Your knee is not swollen.
• You are able to walk, bend and squat without pain.

How can I prevent an anterior cruciate ligament sprain?

You may be able to help avoid injuries to knee ligaments by having strong thigh and hamstring muscles and maintaining a good leg-stretching routine.

Practicing coordinated jumping and landing may help prevent ACL injuries. In activities such as skiing, make sure your ski bindings are set correctly by a trained professional so that your skis will release when you fall.