Informed Patient Tutorial
Copyright 2012 by the American Academy of Orthopaedic Surgeons

Informed Patient - Anterior Cruciate Ligament Reconstruction


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A torn anterior cruciate ligament (ACL) is one of the most common knee injuries. In many of these cases, the ACL is completely torn and may require surgery in order to regain full function in the knee.

The surgical procedure to repair a torn ACL is called an ACL reconstruction. Approximately 150,000 ACL reconstructions are performed in the United States each year.

Because the results from ACL reconstruction continue to improve, more patients are becoming good candidates for this procedure.

This tutorial will explain ACL tears and how they occur. It will discuss nonsurgical treatment options, as well as why you may need surgery. It will help you prepare for surgery and explain what happens during the procedure. This learning module also provides information on the recovery period and what you can expect from the surgery.

There are 10 parts to this learning module. As you work through them, you will be asked whether you understand the information, and you will be reminded to write down any questions you still have. This way, you will be able to bring your questions with you the next time you see your orthopaedic surgeon.

The learning module includes the following sections:

  • Your Knee: The anatomy of the knee is explained.
  • Causes: This section describes some of the ways that ACLs are injured.
  • Symptoms: This section explains some of the signs of an ACL tear.
  • Diagnosis: This section explains how doctors diagnose ACL tears.
  • Nonsurgical Treatment: Some people with ACL tears can be treated without surgery. This section explains nonsurgical treatment options.
  • Surgical Treatment: This section describes some of the aspects of surgical treatment.
  • Your Surgery: This section reviews what you may expect during surgery.
  • After Surgery: This section explains what you may expect after surgery.
  • Risks and Complications: Some risks and complications can be expected with any surgery. This section outlines some of the most common ones associated with ACL reconstruction.
  • Conclusion: This section sums up the information and provides you with an opportunity to add more questions for your doctor.

Your Knee

Three bones meet to form your knee joint: your thighbone (femur), shinbone (tibia), and kneecap (patella).

Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.


Collateral Ligaments

The collateral ligaments are on the sides of your knee. The medial collateral ligament is on the inside of your leg, and the lateral collateral ligament is on the outside. They control the side-to-side motion of your knee and brace it against unusual movement.


Cruciate Ligaments

The cruciate ligaments are inside your knee joint. They cross each other to form an "X" with the anterior cruciate ligament in front and the posterior cruciate ligament in back. The cruciate ligaments control the motion of your knee to the front (anterior) and back (posterior) directions.

Anterior Cruciate Ligament

The anterior cruciate ligament runs diagonally in the middle of the knee. It prevents the tibia from sliding out in front of the femur, and also provides rotational stability to the knee.

This photograph of healthy cruciate ligaments was taken through an arthroscope. The red arrow identifies the ACL, and the blue arrow identifies the posterior cruciate ligament.

The ACL is made up of two separate sections called bundles. The anteromedial bundle controls front-to-back stability. The posterolateral bundle helps control rotational stability.

Arthroscopic image of normal ACL


Two wedge-shaped pieces of cartilage act as "shock absorbers" between your thighbone and shinbone. These are called the medial meniscus and the lateral meniscus. They are tough and rubbery to help cushion the joint and keep it stable.

When people talk about torn cartilage in the knee, they are usually talking about torn meniscus. Meniscal tears can occur at the same time as an ACL injury or may occur in an unstable knee if the ACL has not been reconstructed.

Over time, an injury to the meniscus can lead to arthritis in the knee. In many cases, ACL reconstructions are performed to prevent meniscal damage and arthritis.

Do You Understand?

Do you understand the anatomy of the knee?

Please take a moment now to write down any questions you still have about the anatomy of the knee.

Bring your questions to your orthopaedic surgeon at your next appointment.

Causes of ACL Injury

The anterior cruciate ligament can be injured several ways, including:

  • Changing direction rapidly while running
  • Stopping suddenly
  • Slowing down
  • Landing from a jump incorrectly
  • Direct contact or collision, such as a football tackle

In general, ACL injury is more common in people who participate in high risk sports, such as basketball, football, skiing, and soccer.

Several studies have shown that in certain sports, female athletes are more likely than male athletes to injure the ACL. This may be due to differences in physical conditioning, muscular strength, and neuromuscular control.

Other suggested causes include differences in pelvic and lower extremity (leg) alignment, increased looseness in ligaments, the effects of estrogen on ligament properties, and the anatomy of the knee bones.

Do You Understand?

Do you understand what can cause an ACL injury?

Please take a moment now to write down any questions you still have about the causes of ACL injury.

Bring your questions to your orthopaedic surgeon at your next appointment.


At the moment you injure your ACL, you may feel a tearing within your knee or hear a "popping" noise. Your knee then may give way.

Most people cannot continue with their sporting activities immediately after an ACL injury.

Other common symptoms include:

  • Pain and swelling.

    Within 24 hours, your knee will swell. If ignored, the swelling and pain may get better on its own. However, if you attempt to return to sports, your knee will probably be unstable and you risk causing further damage to the cushioning cartilage (meniscus) of your knee.

  • Loss of full range of motion
  • Tenderness along the joint line
  • Discomfort while walking

Do You Understand?

Do you understand the symptoms of an ACL injury?

Please take a moment now to write down any questions you still have about the symptoms of an ACL injury

Bring your questions to your orthopaedic surgeon at your next appointment.


Physical Examination and Patient History

During your first visit, your doctor will review your symptoms and medical history.

During the physical examination, he or she will test all the structures of your injured knee and compare them to your non-injured knee.

The Lachman test shown here can help your doctor diagnose an ACL injury. During the test, your doctor will keep your thighbone steady and pull your shinbone forward. Increased motion of the shinbone indicates an ACL tear.

Most ligament injuries can be diagnosed with a thorough physical examination of the knee.

Lachman test

Imaging Tests

Imaging tests are used to help your doctor diagnose an ACL injury and discover whether other parts of your knee are injured.


X-rays do not show ligament injuries but can determine if the ligament injury is associated with a broken bone.

In teenagers and adolescents, x-rays can show if the growth centers in the bones are still active (open). This is important because most surgical procedures for ACL reconstruction require drilling through these areas of bone. If the centers remain open, then normal growth of the femur or tibia can be affected by surgery. In younger patients with open growth centers, surgery may be postponed or a different technique may be used.

This x-ray of an adolescent's knee shows active growth plates. The growth plates are areas near the ends of bones from which the bone grows. They are seen as clear lines or spaces going across the bone.

X-ray of adolescent's knee

Imaging Tests

Magnetic Resonance Imaging (MRI) Scans

MRI studies show soft tissues like the anterior cruciate ligament that cannot be seen on plain x-ray.

Your doctor can evaluate the meniscus, cartilage, and other ligaments with an MRI image. An MRI can confirm your doctor's diagnosis of a torn ACL and help plan for your surgery.

The MRI images shown here have been taken from the side. On the left is a healthy ACL. On the right is a torn ACL.

CT Arthrogram (X-ray)

A CT arthrogram can show important parts of your knee (ligament, meniscus, bone) if you are unable to have an MRI.

(Left) A healthy ACL as seen in an MRI image taken from the side. (Right) A torn ACL has caused the joint to become unstable.

Do You Understand?

Do you understand how a doctor diagnoses an ACL injury?

Please take a moment now to write down any questions you still have about how an ACL injury is diagnosed.

Bring your questions to your orthopaedic surgeon at your next appointment.

Nonsurgical Treatment

A torn ACL will not heal without surgery, but nonsurgical treatment can be effective for some patients.

Those who are most likely to have success with nonsurgical treatment are patients who:

  • Have injured only their ACLs and not the menisci or other ligaments
  • Have stable knees that do not give way with turning, pivoting, or sports activity
  • Have sedentary lifestyles and do not participate in high risk sports

The most common nonsurgical options include:

  • Bracing.

    Your doctor may recommend a brace to protect your knee from instability.

  • Physical therapy.

    As the swelling from the injury goes down, a careful rehabilitation program is started. Specific exercises will restore function to your knee and strengthen the leg muscles that support it.

  • Change in lifestyle or activity.

    You may choose to modify your sports activity or participate in sports that put less strain on your knee.

Do You Understand?

Do you understand the nonsurgical ways that some ACL injuries can be treated?

Please take a moment now to write down any questions you still have about nonsurgical treatments.

Bring your questions to your orthopaedic surgeon at your next appointment.

Surgical Treatment

Doctors often recommend ACL reconstruction to patients who:

  • Are active
  • Are involved in sports or jobs that require pivoting or twisting, as well as heavy manual work
  • Have knees that are unstable (who often feel like the knee is giving way)
  • Have combined injuries, such as a meniscus tear along with an ACL tear. About half of all ACL injuries occur along with damage to other parts of the knee.

Do You Understand?

Do you understand why your doctor has recommended surgery to reconstruct your ACL injury?

Please take a moment now to write down any questions you still have about why you are a candidate for reconstructive surgery.

Bring your questions to your orthopaedic surgeon at your next appointment.

Reconstructing the Ligament

An ACL tear cannot be repaired by suturing (stitching) the ligament back together. Even in cases of smaller, partial ACL tears, suturing often has poor results.

To restore knee stability, your doctor will replace your torn ligament with a substitute made of tendon, which is similar to ligament tissue. This substitute is called a graft.

The graft acts as a scaffold or model on which new ligament tissue can grow.

Types of Grafts

Grafts can be obtained from several sources. Grafts from your own body are called autografts. The most common sources of autografts are:

  • The patellar tendon
  • The quadriceps tendon
  • The hamstring tendons
Sources of autografts.

Types of Grafts

The patellar tendon runs between the kneecap and the shinbone. Patellar tendon grafts use the middle third of the tendon along with plugs of bone from the kneecap above and the tibia below.

Hamstring tendons at the back of the thigh, such as the semitendinosus, are taken as tendon only (no bone plugs). They can be doubled over on themselves to increase their strength.

A portion of the quadriceps tendon, which runs from the kneecap to the thigh, can also be used as a graft.

Cadaver grafts, called allografts, eliminate the need to use your own tissue as a graft.

There are advantages and disadvantages to all graft sources. You should discuss graft choices with your orthopaedic surgeon to help determine which is best for you.

A patellar tendon graft.

Do You Understand?

1. Do you understand the different types of grafts?

2. Have you discussed graft choices with your surgeon?

Please take a moment now to write down any questions you still have about ACL grafts.

Bring your questions to your orthopaedic surgeon at your next appointment.

Your Surgery

Scheduling Surgery

In most cases, ACL reconstructions are not done immediately after injury. Most surgeons will wait several weeks. Operating too early can result in knee stiffness after surgery. Waiting a few weeks allows the swelling to subside and the knee to achieve full, pain-free movement before the operation.

If you are less active, your doctor may delay surgery even longer in order to determine the degree of knee instability or to let you schedule the operation at your convenience. In such cases, your doctor may restrict your activity in order to prevent injuries to other parts of the knee, such as the meniscus.

However, if an ACL tear occurs along with a certain type of meniscal tear or other knee injuries, surgery may need to be performed sooner.

Before Surgery

Your orthopaedic surgeon will help you plan and prepare for your surgery. You may need additional tests, such as blood tests, an electrocardiogram (ECG), or a chest x-ray.

Be sure you have discussed your entire medical history with your surgeon, and have provided any medications you are taking.

Your orthopedic surgeon may ask you to make an appointment with your primary doctor to make sure that you have no medical problems that need to be addressed before your surgery.

Anesthesia Evaluation

Before surgery, you will meet with a doctor from the anesthesia department. He or she will review your medical history and discuss anesthesia choices with you.

Anesthesia can be either general (you are put to sleep) or spinal (you are awake but your body is numb from the waist down).

You may also be given a combination of general anesthesia and a regional block. The block, usually injected into the femoral nerve in the front of your leg, will provide pain relief for the first few hours after surgery.

Do You Understand?

1. Do you understand why your surgery may be scheduled a few weeks after your injury?

2. Do you understand what you may need to do before surgery?

3. Do you understand the anesthesia options?

Please take a moment to write down any questions you still have about what happens before surgery.

Bring your questions to your orthopaedic surgeon at your next appointment.

The Procedure

An ACL reconstruction typically takes between 1 and 2 hours. This may vary depending on whether you have damage to other parts of your knee.

The operation is highly technical and requires the use of arthroscopic video equipment, power tools, and sophisticated instruments.

Your surgeon may have an assistant. The assistant may help in positioning your leg, holding instruments, preparing the graft, and closing the incisions.

The Procedure

First, your surgeon will obtain the graft. If he or she uses an autograft, the selected tendon is surgically removed from your body. If your surgeon is using an allograft, the tissue comes frozen and must be thawed before it can be used.

The graft is then prepared and shaped to the correct size for your knee, as shown here.

The graft is prepared and sized.

The Procedure

Surgery to rebuild an anterior cruciate ligament is done with arthroscopy.

During arthroscopy, your doctor inserts a small, thin instrument called an arthroscope into your joint. The arthroscope is about the size of pen. It contains a video camera and displays images on a television screen, giving your doctor a clear view of the inside of your joint.

Your surgeon will first make a small slit in your skin (about the size of a buttonhole) for the arthroscope. Then he or she will fill your knee with saline solution (salt water). This expands the joint and helps your surgeon to see the inside of your knee clearly and in great detail.

The Procedure

To place the graft in the correct position, your surgeon will drill tunnels into the tibia and femur. Then he or she will pull the graft through these tunnels and secure it on both ends with screws or another type of fixation device.

Here the graft has been inserted and pulled through the tibia and femur.

The devices used to hold the graft in place are generally not removed.

The Procedure

This x-ray of an ACL reconstruction shows the position of a patellar tendon graft (superimposed) and bone plug fixation with metal screws.

The graft choice and fixation methods vary among surgeons. The key to success with this procedure is the position of the graft.

Do You Understand?

1. Do you understand the type of graft your surgeon will use?

2. Do you understand the surgical procedure?

Please take a moment now to write down any questions you still have about surgery for ACL reconstruction.

Bring your questions to your orthopaedic surgeon at your next appointment.

After Surgery

In most cases, you will be able to go home on the same day as your surgery. You will need someone to drive you home and assist you during the first days of your recovery.

Your surgeon will most likely put your knee in a brace like the one shown here. You may also need crutches to keep your weight off of your knee.

Some surgeons use cold therapy devices to reduce pain and swelling. You may also need pain medications for a short time after your surgery.

Knee Brace

Physical Therapy

Rehabilitation plays a vital role in getting you back to your daily activities. A physical therapy program will help your knee regain strength and motion.

Physical therapy first focuses on returning motion to your knee and surrounding muscles. It is vital that your knee not lose the ability to fully straighten. For this reason, you will most likely wear a brace for 2 to 4 weeks to keep your leg straight, except when you do your exercises.

When you have completed your early therapy, you will begin a strengthening program designed to rebuild muscles in your leg and protect the new ligament.

Physical Therapy

The final phase of rehabilitation is aimed at a functional return tailored for the athlete's sport.

The long-term success of the surgery depends on the graft developing a blood supply.

Because it takes time for new ligament tissue to grow, it may be 6 to 12 months before an athlete can return to sports after surgery.

Athletes may not reach maximum improvement until 2 years following surgery.

Do You Understand?

1. Do you understand the importance of physical therapy in your recovery?

2. Do you understand how long it may be before you can return to sports?

Please take a moment now to write down any questions you still have about recovering from surgery.

Bring your questions to your orthopaedic surgeon at your next appointment.

Risks and Complications

As with any surgery, there are risks associated with ACL reconstruction. It is important for you to understand the risks before you make a decision to have surgery. Possible surgical complications include:

  • Infection
  • Stiffness
  • Instability and re-injury
  • Graft complications
  • Bleeding


Infection is a risk of any surgery and can occur after ACL reconstruction. You will be given antibiotics before the start of your procedure and they may be continued for up to 24 hours afterward. Antibiotics can help prevent infection but cannot eliminate the risk completely.

Many infections can be treated with antibiotics alone or antibiotics and a drainage procedure. More serious infections may require removal of the ACL graft and any devices (such as screws) that were used to keep the graft in place.


Scar tissue can form inside the joint as a reaction to surgery. Stiffness or loss of motion develops when the scar tissue restricts your ability to bend and straighten your knee. To prevent stiffness, most surgeons will start range of motion exercises during the first few days after surgery. Your surgeon may also ask you to use a CPM (continuous passive motion) machine. This is a device that slowly bends and straightens your knee while you are in a resting position.

Most of the time stiffness will improve with more vigorous therapy and exercise. If it does not, your surgeon may recommend a second surgery to remove the scar tissue.

Instability and Re-injury

Even though you have been given a new ligament, your knee may begin to feel looser or less stable over time. This may be due to stretching of the graft or weakness of some of the other ligaments around the knee.

It is, of course, possible to re-injure and completely re-tear your new ACL, particularly if you are active in sports.

The treatment of instability or re-tearing is the same as for a first time ACL injury—therapy, bracing, or surgical reconstruction.

Graft Complications

Graft complications may result from using either an autograft or an allograft. Both types of graft require implants to fix the graft within the knee. These are usually screws, staples, or a small button. Any of these can move, loosen, or become painful. When this happens they may need to be taken out.

If the graft is taken from the patellar tendon, rupture of the patellar tendon or fracture of the patella can occur. These are rare complications, but do require surgical repair.

Since allografts are taken from cadaver tissue, they are carefully sterilized and tested to make sure they do not carry any diseases such as hepatitis or HIV. There have been no recent reports of disease transmission from properly prepared allografts, but transmission remains a remote possibility.


Bleeding into the joint (hemearthrosis) is one of the more common but less serious problems after ACL reconstruction.

After surgery, there may be bleeding into the joint from bone and soft tissues within the knee. When this happens, your knee joint becomes swollen and painful. It is harder to bear weight and to bend the knee. Most of the time your body will absorb the blood on its own and the swelling will gradually go down. Your surgeon may also insert a needle into the joint to remove the fluid. This will make it easier to continue rehabilitation.

Other Complications

Other less common orthopaedic complications from ACL surgery include injury to nerves and vessels around the knee.

Medical complications such as pneumonia, blood clots, or anesthesia problems are unusual, but are a known risk of any type of surgery.

Do You Understand?

1. Do you understand the risks and complications of ACL reconstruction surgery?

Please take a moment now to write down any questions you still have about the risks and complications of surgery.

Bring your questions to your orthopaedic surgeon at your next appointment.



Arthroscopic ACL reconstruction is a safe and effective technique to treat ligament tears.

Younger athletic patients require reconstruction to prevent further knee injury. For less active and older patients, both surgical and nonsurgical options should be discussed with your surgeon.

ACL reconstruction is typically done as an outpatient. Rehabilitation may take 6 to 12 months.

Your orthopedic surgeon is a highly trained specialist who can answer your questions and provide more information about ACL reconstruction surgery.

Related Topics

For more information about ACL reconstruction and surgery:

  • Anterior Cruciate Ligament Injuries (http://orthoinfo.aaos.org
  • ACL Injury: Does It Require Surgery? (http://orthoinfo.aaos.org
  • Knee Arthroscopy (http://orthoinfo.aaos.org
  • Knee Arthroscopy Exercise Guide (http://orthoinfo.aaos.org

For more information on musculoskeletal health, return to the AAOS OrthoInfo ( website.