Key Points about Anterior Cruciate Ligament (ACL) Injury

  • The ACL is a ligament in the knee that can become torn from abrupt motions that stress the knee.
  • Many cases of a torn ACL result from playing sports such as soccer, skiing or basketball.  
  • Symptoms of an ACL injury include pain, swelling, and hearing a “pop” noise at the time of the event.
  • Treatment for an ACL injury involves a mix of rest and rehabilitation exercises, and in some cases, surgery.
Common related conditions
Knee Strain or Sprain Meniscus Tear or Strain Knee Arthritis Thigh and Lower Leg Fractures Thigh or Calf Strain or Sprain


The anterior cruciate ligament, also commonly known as ACL, is an important ligament in the knee that connects the shinbone to the thighbone. The ACL can become torn from sudden movements that stress the knee, such as abrupt direction changes, stops or starts, or landing on the leg in an awkward position.

Directly following an ACL injury, you will experience pain and swelling in the knee. You may also have heard or felt a “pop” sensation at the time of the event.

Treating an ACL injury involves resting the affected knee, following physical therapy exercises as advised by your doctor, and in some cases, undergoing surgery to repair ligament damage.

Call your doctor if you experience symptoms following an injury that may signal a torn ACL.

ACL injury causes

An ACL injury occurs when an abrupt movement stresses the knee—oftentimes during athletic activity. Common motions that can cause ACL injuries include:

  • Sudden direction changes
  • Pivoting
  • An awkward landing
  • Stops or starts

ACL injuries can also result from a direct hit or trauma to the knee.

ACL injury risk factors

You may be at an increased risk of experiencing an ACL injury if you:

  • Are a woman
  • Wear improper footwear or equipment while exercising or playing sports
  • Play sports on a turf field
  • Have leg muscle weaknesses or imbalances
  • Play sports such as football, basketball, soccer, or skiing

ACL injury symptoms

The main symptom of an ACL injury is intense pain in the knee that begins directly after the event that caused it. This pain may be accompanied by:

  • Swelling in the knee
  • Limited range of motion in the knee
  • Inability to walk or perform other activities
  • An audible “pop” or snapping noise or feeling at the time of the injury

ACL injury complications

An ACL injury may increase your likelihood of developing osteoarthritis in the affected knee, later in life.

ACL injury prevention

Certain physical therapy regimens and strengthening exercises can lower your risk of an ACL injury. Such exercises may aim to strengthen the:

  • Hamstrings and other leg muscles
  • Core
  • Hips
  • Pelvis

You can also lower your risk of injuries by making sure your techniques are correct for your specific sport, and by wearing appropriate and properly fitting sports gear.

ACL injury diagnosis

In most cases, your doctor will be able to diagnose an ACL injury by examining the knee for joint function, tenderness and swelling.

In some cases, your doctor may order imaging tests to assess the degree of damage or rule out other injuries. These tests may include:

  • X-ray
  • MRI scan
  • Ultrasound

ACL injury treatment

Immediately following a knee injury, you can alleviate pain and swelling by ceasing use of the affected leg and icing the injured knee.

Beyond this immediate care, treatment for an ACL injury involves rehabilitating the knee. Rehabilitation may involve:

  • Physical therapy exercises
  • Wearing a knee brace
  • Using crutches

In cases where multiple ligaments in the knee are damaged, your injury is preventing you from walking, or if you wish to return to athletics, surgery may be recommended.

When to seek care

Call your doctor if you have severe knee pain, swelling, and an inability to walk following an injury to the knee.

Next Steps

Your doctor will assess your ACL injury and set up a treatment plan accordingly.

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