The anterior cruciate ligament (ACL) is one of the main ligaments of the knee. This ligament is crucial to the stability of the knee. Since the knee joint is the largest joint in the human body, and so much strain is placed on it, a torn ACL is a common injury in the knee. It frequently occurs during sporting activities


The signs and symptoms of an ACL injury include one or more of the following:

  • A loud “pop” sound or sensation
  • Severe pain
  • Inability to continue using the knee
  • Swelling, which begins within a few hours after injuring the ligament
  • Limited or total loss of range of motion in the knee
  • A feeling of instability, or “giving out” when weight is placed on the knee

Causes and Risk Factors

The majority of ACL tears occur while playing sports or participating in fitness activities that put stress on the knee. This type of injury can occur when:

  • You suddenly slow down or change direction (called cutting)
  • You pivot while your foot is firmly planted on the ground
  • You incorrectly landing after a jump
  • A sudden stop or misstep
  • You receive a direct blow to the knee, or are involved in a collision

A torn ACL is a common injury among professional and recreational athletes, though anyone who steps the wrong way or pivots the knee suddenly can suffer from this injury.


In addition to a medical history, a thorough examination is the most sensitive way to diagnose an ACL injury. The diagnosis can be confirmed by other studies such as:

Other diagnostics include:

  • X-ray scans
  • MRI scans
  • Diagnostic knee arthroscopy, which will allow your doctor to directly see the injury within the knee joint

Treatments and Procedures

Non-surgical methods can be used to treat a torn ACL and can be very effective in the lower demand patient or in the patient who needs to delay surgery.

Non-surgical treatment methods include:

  • Progressive physical therapy
  • The use of a hinged knee brace

If surgery is needed, arthroscopy is the preferred surgical method. During surgery, your orthopaedic surgeon reconstructs the ACL to stabilize the knee, stop the pain, and prevent further buckling.

Reconstruction is necessary during surgery because the ACL cannot be sown, or repaired. In other words, when this ligament is torn, it will not heal. ACL reconstruction involves removing the damaged ligament and replacing it with other tissues. There are several graft options that will be discussed, but patella tendon and hamstring tendons are the most common. If your doctor recommends knee arthroscopy to replace your torn ACL, you will likely go home the same day, as it is generally an outpatient procedure.


Recovery from ACL replacement surgery varies from person to person. For all patients, however, physical therapy is a critical part of a successful surgery. During physical therapy, which will begin immediately after your surgery, you will participate in exercises that strengthen the knee musculature.

It should be noted that the success of ACL reconstructive surgery depends on the dedication of the patient, and the type of physical therapy that he or she receives.

It generally takes most patients four to six months to regain their sense of balance, which is restored through exercise.

Once your pain and swelling cease, the full range of motion in your knee is achieved. When the strength, endurance, and function of the knee returns, you will be able to return to physical activities.

Most patients will recover in 5-6 months. Those who wish to return to higher demand activities and contact sports may take up to a full year to recover.

Frequently Asked Questions:

How will a torn ACL affect the function of my knee?

With the initial injury, patients often hear or feel a “pop” with a sudden onset of pain and inability to return to sports. Walking may prove to be difficult, and often there is gradual swelling and stiffness in the knee. The torn ligament will allow the knee to “buckle” or “give out” with certain pivoting or cutting activities. Sometimes the problem can become so severe that even a simple activity like walking or working around the house will cause instability episodes.

Who should I see for my knee problem?

A severe knee injury requires medical attention to decrease the chance of further damage. Orthopaedic surgeons specialize in the care of injured ligaments, bones, tendons, and joints, and deal with sports medicine injuries on a daily basis.

Should I have surgery?

The decision to have surgery to repair a torn ACL is based on your age, activity level, degree of instability and associated injuries. Some people are able to get back to full activities without surgery by strengthening the surrounding musculature. Many people find that their activity level is decreased because of the torn ACL and desire reconstruction to allow them to return to full activities. In most instances, surgery is successful and will allow a complete recovery. Reconstructing the torn ACL can also help prevent further damage to the knee from chronic injury.

What exactly is performed during surgery?

The torn ACL cannot be sewn back together. Instead, a tendon is substituted for the ACL ligament. This can either be a piece of patellar or hamstring tendon from your body, or a piece of donor tissue. Once the tendon is harvested, it is attached to two long sutures and pulled into place through small holes that the surgeon will make in the knee. It is held in place with two screws while the holes in the bone heal. The screws are normally made of calcium absorbed by the body over time. Once the surgeon decides the knee is sufficiently stable, the knee is closed and dressed.

Will it be painful?

Multiple techniques are available to decrease the likelihood of severe pain following surgery. Your anesthesiologist may use a nerve block before surgery to lessen the likelihood of pain during and after the procedure. Pain medication is also available, and early exercise will help decrease pain.

Will I be on crutches or need a brace after surgery?

Initially, you will be on crutches after surgery to protect the repair. A brace may also be necessary for a few weeks to help provide stability while your muscle strength gradually returns.

Will a torn ACL heal itself?

Unfortunately, the ACL cannot heal itself. Proper medical treatment is required to repair an ACL tear

Is there a way to prevent ACL tears?

There are certain exercises that may reduce the risk of an individual experiencing an ACL tear; these include neuromuscular, balance, and stability exercises which help control the position of the knee when landing and performing activities. Strengthening the musculature within the leg can also help prevent ligamentous stress. More resources for athletes can found at almost any sports training facility.