Anterior Cruciate Ligament (ACL) Injuries

Topic Overview

Illustration of the bones of the knee

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. See a picture of the knee and the ACL.

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 can trap and tear the pads (menisci) that cushion the knee joints. This damage can lead to osteoarthritis.

Sometimes other knee ligaments or parts of the knee are also injured. This includes cartilage such as the menisci, or bones in the knee joint, which can be broken.

What causes an ACL injury?

Your ACL can be injured if your knee joint is bent backward, twisted, or bent side to side. The chance of injury is higher if more than one of these movements occurs at the same time. Contact (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 are changing direction rapidly, slowing down when running, or landing 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. Like any other body part, the ACL becomes weaker with age. So a tear happens more easily in people older than age 40.

What are the symptoms?

Symptoms of an 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 ACL deficiency is the knee buckling or giving out, sometimes with pain and swelling. This can happen when an ACL injury is not treated.

How is an ACL injury diagnosed?

Your doctor can tell whether you have an ACL injury by asking questions about your past health and examining 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, movement, and tenderness in both the injured and uninjured knee.

You may need X-rays, which can show damage to the knee bones. Or you may need other imaging tests, such as an MRI. An MRI can show damage to ligaments, tendons, muscles, or knee cartilage. Arthroscopy may also be done. During arthroscopy, your doctor inserts surgical tools through one or more small cuts (incisions) in the knee to look at the inside of the knee.

How is it treated?

Start first aid right away. These first-aid tips will reduce swelling and pain. Use the RICE method. The letters stand for Rest the knee, put Ice on it, use an elastic bandage to give gentle Compression to the knee, and Elevate the leg by propping it up above the level of your heart. And it’s also important to move your leg as little as possible. Take over-the-counter pain medicine.

You may need to walk with crutches and use a knee immobilizer to keep your knee still for the first few days after the injury.

Your knee will need to be checked by your doctor. It's important to get treatment. If you don't, the injury may become a long-lasting problem. There are two ways to treat the injury:

  • 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.

Your treatment will depend on how much of the ACL is torn, whether other parts of the knee are injured, how active you are, your age, your overall health, and how long ago the injury occurred.

There are three main treatment goals:

  • Make the knee stable if it is unsteady, or at least make it stable enough to do your daily activities.
  • Make your knee strong enough to do all the activities you used to do.
  • Reduce the chance that your knee will be damaged more.

How can you prevent ACL injuries?

The best way to prevent ACL injuries is to stretch and strengthen the leg muscles, especially the front and back muscles of the thigh (quadriceps and hamstrings).

Other things you can do that may help prevent ACL injuries include:

  • Avoid wearing shoes with cleats in contact sports.
  • Avoid wearing high-heeled shoes.
  • Avoid sports that involve lots of twisting and contact.

Frequently Asked Questions

Learning about anterior cruciate ligament (ACL) injuries:

Being diagnosed:

Getting treatment:

Living with an ACL injury:

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  ACL injury: Should I have knee surgery?

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  ACL injury: Exercises to do before treatment

Cause

Anterior cruciate ligament (ACL) injuries are caused when the knee is straightened beyond its normal limits (hyperextended), twisted, or bent side to side.

Typical situations that can lead to ACL injuries include:

  • Changing direction quickly or cutting around an obstacle or another player with one foot solidly planted on the ground (as can happen in sports that put high demand on the ACL such as basketball, football, soccer, hockey, and gymnastics).
  • Landing after a jump with a sudden slowing down, especially if the leg is straight (such as in basketball).
  • Falling off a ladder, stepping off a curb, jumping from a moderate or extreme height, stepping into a hole, or missing a step when walking down a staircase. Injuries from these situations tend to be caused by stopping suddenly, with the leg straight.

Inactive people and some older adults who have weak leg muscles may injure their knees during normal daily activities. But they usually injure bones, not ligaments.

When contact causes an ACL injury, it can be from playing a sport, from a sudden and severe accident, or from less obvious contact injuries. In football, receiving a clipping contact injury—in which the bent knee is struck from the outside—can cause an ACL injury. Clipping often damages several knee structures at the same time, including the ACL, the medial collateral ligament (MCL), and the pads in the knee (menisci) that protect and cushion the joint surface and bone ends. Clipping injures the medial meniscus more often than the lateral meniscus.

An ACL injury may develop into long-lasting and recurrent (chronic) ACL deficiency that leads to an unstable knee—the knee buckles or gives out, sometimes with pain and swelling. This can occur if your ACL has not been treated or has been treated unsuccessfully, or if you had an ACL injury in the past and did not know it.

Symptoms

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

  • Feeling or hearing a "pop" in the knee at the time of injury.
  • Sudden instability in the knee (the knee feels wobbly, buckles or gives out) after a jump or change in direction or after a direct blow to the side of the knee.
  • Pain on the outside and back of the knee.
  • Knee swelling within the first few hours of the injury. This may be a sign of bleeding inside the joint (hemarthrosis). Swelling that occurs suddenly is usually a sign of a serious knee injury.
  • Limited knee movement because of swelling and/or pain.

After an acute injury, you will almost always have to stop the activity you are engaged in but may be able to walk.

The main symptom of chronic (long-lasting and recurrent) ACL deficiency is an unstable knee joint. The knee buckles or gives out, sometimes with pain and swelling. This happens more often over time. But not everyone with an ACL injury develops a chronic ACL deficiency.

Other conditions with symptoms similar to ACL knee pain include injuries to other knee structures, such as:

  • An injury to the cartilage lining the knee joint.
  • An injury to the knee cushions (menisci). About 70% of people with an ACL injury also have a meniscus tear.1
  • An injury to the knee ligaments that connect the upper leg bone to the lower leg bone along the inner side of the knee joint (medial collateral ligament) and the outer side of the knee joint (lateral collateral ligament).
  • A break (fracture) in the bones of the knee joint.

For more information on knee injuries, see the topics Knee Problems and Injuries and Patellar Tracking Disorder.

What Happens

If you have a sudden (acute) anterior cruciate ligament (ACL) injury, you generally know when it happens. You may feel or hear a pop and the knee may give out, causing you to fall. The knee swells and often is too painful or unstable to continue any activity.

An ACL injury can cause small or medium tears of the ligament, a complete tear of the ligament (rupture), a separation of the ligament from the upper or lower leg bone (avulsion), or a separation of the ligament and part of the bone 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.

When the ACL ligament tears, the blood vessels around the ligament tear and blood fills the knee joint, causing swelling. When you see a doctor, he or she may not be able to examine the knee thoroughly because of the swelling.

Other parts of the knee can be injured at the same time. These may include one of the pads that act as cushions between the two leg bones (menisci), another knee ligament (medial collateral ligament or lateral collateral ligament), or the dense tissue that covers the ends of bones (cartilage). The bones of the knee joint may also be broken (fractured).

Diagnosis may not be done at the time of injury. Sometimes people think the injury is not serious, especially if the knee gets better in a few days. In this case, or if the diagnosis is missed during the initial examination, the injury may develop into a long-lasting and recurrent (chronic) ACL deficiency, in which the knee moves abnormally and gives way occasionally. This can potentially cause progressive damage to the joint, including osteoarthritis. But not everyone with an ACL injury develops a chronic ACL deficiency.

The course of an ACL injury depends on:

  • The condition of the ACL before this injury, including prior injuries, partial tears, ACL deficiency, and degenerative changes due to age.
  • The general condition and health of all of your knee structures prior to this injury.
  • The amount of damage or injury to the ACL. Injuries to the ACL are usually grouped into grade I, II, or III sprains (tears) according to the amount of damage.
  • Additional injuries to the knee joint, such as to the cartilage or menisci, or to bones in the knee.
  • Your age, how active you are, and how committed you are to treatment and rehabilitation.
  • The time of diagnosis. If the ACL diagnosis is not made soon after the injury, the knee may be further damaged with use.

People with minor ACL injuries usually begin treatment with a physical rehabilitation program. Rehabilitation exercises build strength and flexibility in the muscles on the front of the thigh (quadriceps) and strengthen and tighten the muscles in the back of the thigh (hamstrings). You may use crutches for a short time. Although knee braces may be used to stabilize the knee immediately after injury, they are not usually used long-term. Most people return to their normal activities after a few weeks of rehabilitation.

More serious ACL injuries may require several months of rehabilitation or surgery followed by several months of rehabilitation to regain your knee strength, knee stability, and range of motion. You may use crutches or special knee braces, and it may take several months to a year until you can return to your previous level of activity. The rehabilitation program is intensive—many people think of it as having a second job.

Not all ACL injuries require surgery, but whether you have surgery or not, you need to start strengthening your knee and regaining motion soon after you injure it. This prepares you for your rehabilitation program if you choose not to have surgery and also helps prepare the knee for surgery if you choose to have it.

What Increases Your Risk

Factors that increase your risk of anterior cruciate ligament (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.
  • Making accidental movements that may twist your knee, such as falling off a ladder, jumping from an extreme height, stepping into a hole, or missing a step on a staircase.
  • Losing muscle tone in legs (from aging or inactivity).
  • 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).
  • Previous ACL injuries, especially if your knee sometimes gives out or buckles (chronic ACL deficiency).

Women have more ACL injuries than men. In sports, women injure their ACL up to 8 times as often as men. There are several theories for the increased incidence in women athletes, including differences in men's and women's bodies and how they use muscles, and training that does not help make up for these differences.2, 3

When To Call a Doctor

Call your doctor immediately if you have an injury to your knee and:

  • You have severe pain in your knee.
  • Your knee appears to be deformed.
  • You have signs of damage to the nerves or blood vessels, such as numbness, tingling, a "pins-and-needles" sensation below the injury, an inability to move your leg below the injury, pale or bluish skin, or your leg feels cold.

Call your doctor today if:

  • Your knee begins to swell within 2 hours of the injury.
  • You hear or feel a pop in your knee during an injury.
  • Your knee won't bear weight.
  • You are unable to straighten your leg completely.
  • Your knee is unstable, buckles, or gives out.
  • Your knee “locks” in one position.
  • You have had an anterior cruciate ligament (ACL) injury in the past and you have reinjured your knee.

Before your appointment, do not put weight on the injured knee. Use crutches if necessary. Apply ice and wrap your knee in an elastic bandage or neoprene (synthetic rubber) sleeve. Rest and elevate the knee. Take a nonprescription anti-inflammatory drug to reduce swelling. For more information on first aid steps, see the Home Treatment section of this topic.

Watchful Waiting

Watchful waiting is a period of time during which you and your doctor observe your symptoms or condition without using medical treatment. Watchful waiting is not appropriate if knee pain is severe, your knee is deformed or swells immediately after an injury, or you are unable to bear any weight, either because of pain or instability.

Serious knee injuries need to be checked for possible broken bones as well as ligament or cartilage damage. Whenever immediate swelling follows an injury, there also may be torn blood vessels or damaged nerves in the knee. Your doctor will check your knee to make sure the blood supply to your leg is normal and the nerves are intact.

If you have occasional pain in your knee or your knee sometimes gives way or buckles, have your doctor check it. If you have damaged your ACL, it is important to get treatment so that your knee is appropriately managed, which may reduce the chance that you will get osteoarthritis in your knee.

Who To See

Knee problems can be diagnosed by:

If surgery is considered, you may be referred to an orthopedic surgeon (possibly a sports medicine specialist) who is experienced in knee surgery.

To prepare for your appointment, see the topic Making the Most of Your Appointment.

Exams and Tests

An anterior cruciate ligament (ACL) injury is diagnosed through a medical history and a physical examination. A doctor who specializes in knee injuries (for example, an orthopedic surgeon or sports medicine specialist) will usually be able to accurately diagnose an ACL injury after:

  • Taking your medical history. You will be asked how you injured your knee, about your symptoms at the time of injury, whether you have had any other knee injuries, and general questions about your health.
  • Checking your knees for stability, strength, range of movement, swelling, and tenderness. Tests for stability include a Lachman test and a pivot shift test. The Lachman test compares the degree of looseness (laxity) in your knees.
  • Looking at an X-ray, which is usually done for any knee injury. Although an ACL injury cannot be directly diagnosed by an X-ray, it can determine whether a bone is broken, any bone fragments are in the knee, the ACL is torn from the bone (avulsion), or blood is present in the knee (effusion).

If you see your doctor soon after your injury, the pain and the degree of swelling and muscle tenseness may make it difficult for your doctor to accurately diagnose the condition.

Other tests that may help determine how badly the knee is injured include:

If your knee is red, hot, or very swollen, a knee joint aspiration (arthrocentesis) may be done, which involves removing fluid from the knee joint with a syringe (needle). This is done to:

  • Help relieve pain and pressure, which may make the physical exam easier and make you more comfortable.
  • Check joint fluid for possible infection or inflammation.
  • Identify blood, which may indicate a tear.
  • Identify drops of fat, which may indicate a broken bone.

Fluid removed from the knee joint may be tested to identify blood and fatty droplets from a hidden fracture. Local anesthetic may be injected to reduce pain and make the knee easier to examine. If the ACL is torn, fluid drained from the knee may contain a lot of blood.

Arthrometric testing of the knee may also be done. In this test, your doctor uses an instrument to measure the looseness of your knee. This test is especially useful in people whose pain or physical size makes a physical exam difficult. An arthrometer has two sensor pads and a pressure handle that allows your doctor to put force on the knee. The instrument is strapped to your lower leg so that the sensor pads are placed on the knee cap and the small bump just below it (tibial tubercle). Your doctor then measures pressure by pulling or pushing on the pressure handle.

Arthroscopy is another procedure used in the diagnosis of an ACL injury and is also usually used as a method of surgery. Arthroscopy involves inserting instruments through one or more small incisions in the knee, allowing your doctor to examine the structures inside the knee joint, including the ACL.

Before arthroscopy, you and your doctor will decide what will be done if certain conditions are found. For example, you may decide in advance that if a complete tear of the ACL is found, it will be reconstructed during the arthroscopy. Or, if a more severe condition is found, you and your doctor may agree to discuss the condition rather than proceeding with surgery at that time.

Treatment Overview

There are three main treatment goals. The first goal is to stabilize the knee if it is unstable—or at least stabilize it enough to suit your lifestyle. The second goal is to return your knee to normal or almost normal functioning. The third goal is to reduce the likelihood of further damage to the knee. Treating anterior cruciate ligament (ACL) injuries may also help to reduce pain, prevent osteoarthritis, and prevent loss of strength and decreased movement in the knee.

Initial treatment of an acute ACL injury consists of using first aid steps to stabilize your knee and reduce swelling and pain.

Later treatment may include several months of rehabilitation or surgery with rehabilitation. Not all ACL tears require surgery. Further treatment is nearly always a decision you and your doctor make between rehabilitation only and surgery plus rehabilitation.

Acute (sudden) ACL injuries

If you know you have injured your ACL, initial treatment consists of:

  • First aid steps to reduce swelling and pain. This may include resting the knee, applying ice, using gentle compression with an elastic bandage, elevating the leg, and taking pain medicines, such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs).
  • Using crutches and/or immobilizing splints in the first few days after an injury. If crutches or splints are used for too long, the muscles will become weaker from too little activity, and movement of the knee will become stiff and restricted.
  • Strength and motion exercises to help prepare you for treatment. For more information, see:
    Click here to view an Actionset.ACL injury: Exercises to do before treatment.

For information on specific first aid steps to take immediately after the injury, see the Home Treatment section of this topic.

Further treatment

After initial treatment for an anterior cruciate ligament (ACL) injury, further treatment of the injury depends on:

  • How much of your ACL is torn (whether it is a grade I, II, or III sprain).
  • When the injury occurred and how stable your knee is.
  • Whether other parts of the knee are injured. If other parts of your knee are injured, it will be harder for the strong parts of your knee to compensate and protect the injured parts.
  • Preexisting conditions of the knee, such as prior injuries that resulted in long-term (chronic) ACL deficiency, or osteoarthritis.
  • How active you are.
  • Your age and overall health status.
  • Your willingness and ability to complete a long and rigorous rehabilitation.

Treatment options include:

  • Nonsurgical treatment only, such as a physical rehabilitation program.
  • ACL surgery to reconstruct the ACL or to reconstruct the ACL and repair injuries that occurred at the same time, such as a meniscus tear. Most ACL surgery is done by making small incisions in the knee and inserting instruments for surgery through these incisions (arthroscopic surgery). Open surgery (cutting a larger incision in the knee) is sometimes required. Physical rehabilitation always follows surgery.

For more information, see:

Click here to view a Decision Point. Should I have surgery for an ACL injury?

Recovery from an ACL injury varies with each individual. Your treatment should continue until your knee is stable and strong, not for a certain length of time.

Treatment in children and teens

Anterior cruciate ligament (ACL) injuries in children and teens are less common than in adults, but they do occur, especially in teens. An untreated or unsuccessfully treated ACL injury in children or teens may result in future knee problems. The knee may become more and more unstable and, over time, osteoarthritis may develop.

A child with an ACL injury can sometimes be treated without surgery in order to avoid damage to the child's still-developing bones. Nonsurgical treatment includes rehabilitation exercises, wearing a brace, and avoiding activities that require jumping or twisting. Nonsurgical treatment is not always successful. A child's level of activity is a strong factor in how successful treatment is. Studies suggest that the more active a child is, the less likely nonsurgical treatment will be successful and the more likely surgery will be needed in the future.4

An avulsion fracture (a separation of the ligament and a piece of the bone from the rest of the bone) is more common in young children. It can often be treated with a cast but sometimes needs surgery.

Surgery in a child might be necessary to prevent injury to other structures within the knee, such as the menisci. You may consider surgery if the child's knee is very unstable doing simple daily activities, if the knee's instability cannot be controlled with nonsurgical methods, if the child has both an ACL injury and a meniscus tear, or if the child is a serious athlete in sports that require running, jumping, and decelerating. Postsurgery rest and a sustained rehabilitation program are extremely important.5

The main risks of surgery in a child whose bones are still growing is slowed growth (physeal arrest), which may result in one leg being longer than another. Other risks include the thigh bone pointing inward (distal femoral valgus or angular limb deformity). The closer a child or teen is to skeletal maturity, the lower the risk of these conditions.

What To Think About

Things that you should consider about treatment options include:

  • Your goals for recovery. How stable and strong do you want your knee to be? What activities do you hope to return to?
  • How motivated you are to complete a long and rigorous rehabilitation program. Are you able to complete a rehabilitation program?

Depending on how severe your injury is, surgery with rehabilitation may offer the best chance of making your knee stable again and of continuing an active lifestyle without further pain, injury, or loss of strength and movement in your knee. Age is not a factor, although your overall health may be. Surgery may be done for adults at any age who want to continue activities that require a strong, stable knee.

If your initial injury resulted in an unstable knee that occasionally gives out (chronic ACL deficiency) and you continue to participate in activities that require a stable knee and don't have surgery, you may injure your knee again.

You will need to follow a rehabilitation program whether or not you have surgery. If you do not complete a rehabilitation program, even with surgery you may not regain full stability and function in your knee.

You may choose to start a rehabilitation program to avoid or delay knee surgery by strengthening and developing flexibility in the muscles that support the knee (hamstrings and quadriceps). If you eventually need surgery, you will be much better conditioned for it and for the rehabilitation that follows.

An avulsion fracture (a separation of the ligament and a piece of the bone from the rest of the bone) is rare in adults. But when this fracture occurs in adults, surgery may be needed to reattach the bones.

Prevention

The best way to prevent anterior cruciate ligament (ACL) injuries is to stretch and strengthen the leg muscles, especially the front and back muscles of the thigh (quadriceps and hamstrings).

Other precautions that may help prevent ACL injuries include:

  • Avoid wearing shoes with cleats in contact sports.
  • Avoid wearing high-heeled shoes.
  • Avoid sports that involve lots of twisting and contact.

If you have already had an ACL injury, you can avoid another ACL injury by:

  • Strengthening the injured knee through rehabilitation exercises.
  • Changing your sports techniques to avoid motions that might stress the injured knee.
  • Changing your lifestyle to avoid sports that have a high risk of injuring your knee further, such as skiing, football, soccer, or basketball.
  • Wearing a knee brace during high-risk activities. But braces should be used only if rehabilitation is also being done. Wearing a brace alone may be of little benefit and may give you a false sense of security.

Programs to prevent ACL injuries are available. These programs generally emphasize injury awareness, avoidance techniques, and stretching, strengthening, and jumping exercises to help reduce ACL injuries.

Tips to prevent ACL injuries include practicing landing after jumps with the knees bent and crouching when pivoting and turning.

Home Treatment

If you have an acute (sudden) anterior cruciate ligament (ACL) injury, use the following first aid steps to reduce pain and swelling:

  • Rest and reduce your activity level. Use crutches if it hurts to put weight on your knee, until you can see your doctor. Crutches can be rented from most pharmacies. When you call for an appointment, tell your doctor that you are using crutches. Crutches should not be used for long because a lack of activity can cause muscle tissue to waste away and result in restricted movement of the knee.
  • Ice your knee. To avoid a freeze-burn, do not put the ice directly on your skin. Put a cloth or towel between the ice and your knee.
  • Elevate your knee while applying ice or any time you are sitting or lying down.
  • Wrap your knee with an elastic bandage or neoprene sleeve (available at a pharmacy). This may help ease pain during movement and reduce fluid inside the knee. Don't wrap your knee too tightly, as this may cause swelling below the bandage. Loosen the bandage if it is too tight. Signs of an overly tight bandage include numbness, tingling, increased pain, and coolness in the foot.
  • Take medicine such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce your pain.

After diagnosis of an ACL injury, your doctor may suggest exercises that help strengthen your leg and increase your range of motion. They may be the start of your nonsurgical treatment program or be used to help prepare your knee for surgery. For more information, see:

Click here to view an Actionset. ACL injury: Exercises to do before treatment.

Medications

Medicine is used for an anterior cruciate ligament (ACL) injury to relieve or reduce pain. It also may be used for long-term (chronic) ACL deficiency and during the rehabilitation period. Nonprescription pain medicines such as acetaminophen (Tylenol, for example) or nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, are commonly used.

NSAIDs may cause stomach upset and should be taken with food and a glass of water. They can have side effects and should not be taken with certain other medicines. Let your doctor know what other medicines you are taking. Do not give aspirin to anyone younger than 20 because of the risk of Reye's syndrome.

Surgery

Most surgery for anterior cruciate ligament (ACL) injuries involves replacing the ACL with tissue called a graft. Usually an autograft (tendon tissue taken from another part of the body) is used. Repair is also done when the ACL has been torn from the upper or lower leg bone (avulsion). This type of injury is uncommon. In the case of an avulsion fracture, the bone fragment connected to the ACL is reattached to the bone.

Most ACL surgery is done by making small incisions in the knee and inserting instruments for surgery through these incisions (arthroscopic surgery). Open surgery (cutting a large incision in the knee) is sometimes required.

The goals of surgical treatment for anterior cruciate ligament (ACL) injuries are to:

  • Restore normal or almost normal stability in the knee.
  • Restore the level of function you had before the knee injury.
  • Limit loss of function in the knee.
  • Prevent injury or degeneration to other knee structures.

Surgical techniques and rehabilitation programs used today generally are successful. Between 80% and 90% of people who have ACL surgery have favorable results, with reduced pain, good knee function and stability, and a return to normal levels of activity.6 Unfortunately, 3% to 10% of people who have ACL surgery still have knee pain and instability.7 Athletes and those who participate in sports generally can return to their sports within months, depending on how intense and sports-focused the rehabilitation was.

Not all ACL tears require surgery. You and your doctor will decide whether rehabilitation only or surgery plus rehabilitation is right for you. For more information, see:

Click here to view a Decision Point. Should I have surgery for an ACL injury?

Before ACL surgery, strength and motion exercises are often done to help condition the knee for surgery and the subsequent rehabilitation program. Surgery is followed by a short period of performing home exercises, increased activity, and the use of crutches for walking. An intensive rehabilitation program to strengthen the knee then begins. The rehabilitation program often lasts up to a year. For more information, see:

Click here to view an Actionset. ACL injury: Exercises to do before treatment.

Surgery in a child might be necessary to prevent injury to other structures within the knee, such as the menisci. You may consider surgery if the child's knee is very unstable doing simple daily activities, if the knee's instability cannot be controlled with nonsurgical methods, if the child has both an ACL injury and a meniscus tear, or if the child is a serious athlete in sports that require running, jumping, and decelerating. Postsurgery rest and a sustained rehabilitation program are extremely important.5

The main risks of surgery in a child whose bones are still growing is slowed growth (physeal arrest), which may result in one leg being longer than another. Other risks include the thigh bone pointing inward (distal femoral valgus or angular limb deformity). The risks of these conditions is lower the closer a child or teen is to skeletal maturity.

Surgery Choices

ACL surgery

What To Think About

  • Depending on how severe your injury is, surgery followed by a rehabilitation program may offer the best chance of making your knee stable again and of your continuing an active lifestyle without further pain, injury, or loss of strength and movement in your knee. Without surgery, it is more likely that loss of knee function, osteoarthritis, and other knee problems will develop later.
  • In adults, age is not a factor in surgery, although your overall health may be. Surgery may not be the ideal treatment for people with medical conditions that make surgery a greater risk. These people may choose nonsurgical treatment and try to change their activity level to protect their knee from further injury.
  • Surgery is sometimes delayed until the swelling goes down, you have full range of motion in your knee again, and you can strongly contract (flex) the muscles in the front of your thigh (quadriceps). You and your doctor decide on the timing of your surgery.
  • Whether you have surgery soon after the injury or weeks later does not seem to affect recovery significantly.3
  • You will need to follow a rehabilitation program whether or not you have surgery. If you do not complete a rehabilitation program, even with surgery you may not regain full stability and function in your knee.
  • If your initial injury resulted in an unstable knee that sometimes gives out (chronic ACL deficiency) and you continue participating in activities that require a stable knee and don't have surgery, you may injure your knee again.
  • Possible complications of arthroscopic knee surgery include a loss of motion (most common), pain that does not go away, fluid in the knee joint (postoperative effusion), damage to the knee cartilage from the arthroscope scraping against it, and infection. Other risks include a blood clot in the leg, and in extremely rare circumstances, this blood clot can migrate to the lungs and block blood flow out of the lungs (pulmonary embolism).

You may choose to have surgery if you:

  • Have completely torn your ACL or have a partial tear and your knee is very unstable.
  • Have gone through a rehabilitation program and your knee is still unstable.
  • Are very active in sports or have a job that requires knee strength and stability (such as construction work), and you want your knee to be as strong and stable as it was before your injury.
  • Are willing to complete a long and rigorous rehabilitation program.
  • Have a chronic ACL deficiency.
  • Have injured other parts of your knee, such as the cartilage, meniscus, other knee ligaments, or tendons, or you have broken bones in the knee joint.

You may choose not to have surgery if you:

  • Have a minor tear in your ACL (a tear that can heal with rest and rehabilitation).
  • Are not very active in sports or your work does not require a stable knee.
  • Are willing to stop doing activities that require a stable knee or stop doing them at the same level of intensity. You may choose to substitute other activities that don't require a stable knee, such as cycling or swimming.
  • Can complete a rehabilitation program that stabilizes your knee and strengthens your leg muscles to reduce the chances that you will injure your knee again and are willing to live with a small amount of knee instability.
  • Do not feel motivated to complete the long and rigorous rehabilitation program necessary after surgery.

Other Treatment

Other treatment for anterior cruciate ligament (ACL) injuries includes physical rehabilitation to:

  • Restore function and stability in the knee.
  • Strengthen muscles around the knee.
  • Protect the ACL and your knee joint from further injury.
  • Allow you to return to most activities that you did before the injury. If rehabilitation is done without surgery, recurrent instability may be a problem during some movements.

You may choose to treat an ACL injury with rehabilitation alone. If you have surgery, rehabilitation will also be part of your treatment.

Other Treatment Choices

Physical rehabilitation

What To Think About

Physical rehabilitation to treat ACL injuries, both with and without surgery, can be a long and rigorous program.

Physical rehabilitation done before surgery helps your recovery after surgery.

Some people who initially choose not to have surgery eventually need to have it.

People who choose not to have ACL surgery may be less likely to return to competitive sports than those who choose to have it.

Other Places To Get Help

Organizations

American Academy of Orthopaedic Surgeons (AAOS)
6300 North River Road
Rosemont, IL  60018-4262
Phone: 1-800-346-AAOS (1-800-346-2267)
(847) 823-7186
Fax: (847) 823-8125
E-mail: pemr@aaos.org
Web Address: www.aaos.org
 

The American Academy of Orthopaedic Surgeons (AAOS) provides information and education to raise the public's awareness of musculoskeletal conditions, with an emphasis on preventive measures. The AAOS Web site contains information on orthopedic conditions and treatments, injury prevention, and wellness and exercise.


American College of Sports Medicine (ACSM)
P.O. Box 1440
Indianapolis, IN  46206-1440
Phone: (317) 637-9200
Fax: (317) 634-7817
Web Address: www.acsm.org
 

The American College of Sports Medicine (ACSM) provides general information and publications about exercise and sports medicine.


References

Citations

  1. Shea MA, et al. (2003). Knee pain, swelling, and instability. Physician and Sportsmedicine, 31(9): 31–33.
  2. Seroyer S, West R (2007). Anterior cruciate ligament section of Injuries specific to the female athlete. In PJ McMahon, ed., Current Diagnosis and Treatment in Sports Medicine, pp. 259–260. New York: McGraw-Hill.
  3. D'Amato MJ, Rach BR Jr (2003). Anterior cruciate ligament reconstruction in the adult section of Anterior cruciate ligament injuries. In JC DeLee, D Drez Jr, eds., Orthopaedic Sports Medicine, 2nd ed., vol. 2, pp. 2012–2067. Philadelphia: Saunders.
  4. Shea KG, et al. (2003). Anterior cruciate ligament injury in paediatric and adolescent patients. A review of basic science and clinical research. Sports Medicine, 33(6): 455–471.
  5. Silbey MB, Fu FH (2001). Anterior cruciate ligament. In FH Fu, DA Stone, eds., Sports Injuries: Mechanisms, Prevention, Treatment, 2nd ed., pp. 1115–1121. Philadelphia: Lippincott Williams and Wilkins.
  6. Fu FH, et al. (2000). Current trends in anterior cruciate ligament reconstruction. American Journal of Sports Medicine, 28(1): 123–130.
  7. Noyes FJ, Barber-Westin SD (2001). Revision anterior cruciate ligament reconstruction: Report of 11-year experience and results in 114 consecutive patients. AAOS Instructional Course Lectures, 50: 451–461.

Other Works Consulted

  • Grant JA, et al. (2003). ACL reconstruction with autografts. Physician and Sportsmedicine, 31(4): 27–32, 40.
  • Grudziak JS, Musahl V (2007). Anterior cruciate ligament tear section of The youth athlete. In PJ McMahon, ed., Current Diagnosis and Treatment in Sports Medicine, pp. 213–220. New York: McGraw-Hill.
  • Miller SL, et al. (2002). Graft selection in anterior ligament reconstruction. Orthopedic Clinics of North America, 33(4): 675–683.
  • Trees AH, et al. (2006). Exercise for treating isolated anterior cruciate ligament injuries in adults. Cochrane Database of Systematic Reviews (3). Oxford: Update Software.

Credits

Author Shannon Erstad, MBA, MPH
Editor Kathleen M. Ariss, MS
Associate Editor Pat Truman, MATC
Associate Editor Michele Cronen
Primary Medical Reviewer Adam Husney, MD - Family Medicine
Primary Medical Reviewer William M. Green, MD - Emergency Medicine
Specialist Medical Reviewer Freddie H. Fu, MD - Orthopedic Surgery
Specialist Medical Reviewer Patrick J. McMahon, MD - Orthopedic Surgery
Last Updated May 16, 2008

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