Anterior Cruciate Ligament Injury
all information

Anterior Cruciate Ligament Injury

(ACL Injury)

Pronounced: an-TEER-ee-or KROO-shee-ate ligament

En Español (Spanish Version)


An anterior cruciate ligament (ACL) injury is a tear in the ACL ligament. The ACL is located in the middle of the knee joint and connects the lower leg bone to the thigh bone. It stabilizes the knee by preventing the thigh bone from sliding too far forward at the knee.

Anterior Cruciate Ligament Injury

ACL injury

© 2008 Nucleus Medical Art, Inc.


Most ACL tears occur during non-contact injuries, such as:

  • Planting the foot and cutting
  • Pivoting
  • Landing on a straight leg
  • Making a sudden stop

The ACL can also be injured from a direct blow to the knee.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

  • Sex: female
  • Muscle imbalance between the quadriceps and hamstrings (weaker hamstrings)
  • Weak quadriceps and hamstrings
  • Playing sports that require sudden changes of direction and deceleration
  • Incorrect technique for cutting, planting, pivoting, or jumping


When the ACL tears, you may hear a popping sound. As you stand, the knee will probably give-way immediately, and it will be difficult to walk on the affected leg. There is usually moderate pain and swelling of the knee joint, although in the first several hours, this may be minor. It will, however, worsen over the first two days, and then begin to subside.


The doctor will ask about your symptoms and how you injured your knee. A physical exam will be performed.

Tests may include:

  • MRI scan—a test that uses magnetic waves to show the structures inside the knee joint
  • Arthroscopy—a thin, lighted tube inserted through a small incision in the knee to look at the structures inside the knee


Treatments include:

Knee Brace

You may need to wear a knee brace while recovering from your knee injury. The brace may also be needed when you return to your sport. This may be needed whether or not you have surgery to reconstruct the ligament.


Surgery may be needed to fully restore function of the knee. The decision to have surgery should be made after discussion with your doctor about your athletic needs, age, and associated factors.

Physical Therapy

  • Range of motion exercises—The therapist will assist you with moving your knee through its full range of motion. Stretching is a part of this treatment.
  • Strengthening exercises—Due to its lack of use, the affected leg muscles will atrophy (shrink) and lose strength. Therapy will help you regain strength in the thigh muscles, especially the quadriceps and hamstrings.


ACL tears are often due to noncontact injuries. Precautions can be taken to prevent them.

  • When jumping and landing, or turning and pivoting, your hips and knees should be bent, not straight
  • Incorporate adequate warm-up exercises to prepare the knee for your sport
  • Plyometrics, a form of jumping exercises, can be used to train and strengthen the leg muscles for jumping and landing (should only be done under professional supervision)
  • Strengthen both the quadriceps and the hamstrings
  • Keep the quadriceps and hamstrings flexible by stretching regularly


American Academy of Orthopaedic Surgeons

Women's Sport Foundation


Canadian Orthopaedic Association

Canadian Orthopaedic Foundation


ACL Injury: Does It Require Surgery? American Academy of Orthopaedic Surgeons website. Available at: Accessed June 18, 2008.

Griffin LY, Agel J, Albohm M, et al. Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. J Am Acad Orthop Surg. 2000;8:141-150.

Wells C. Women, Sport & Performance. Champaign, Ill: Human Kinetics;1991.

Last reviewed October 2007 by Robert E. Leach, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

Your Health and Happiness