Anterior Cruciate Ligament (ACL) Injuries

The anterior cruciate ligament (ACL) is the primary restraint that limits how far the tibia (shin bone) slides forward in relation to the femur (thigh bone). When the ACL tears and that restraint disappears, the knee becomes unstable and may unpredictably buckle or give way. An ACL tear is a common knee injury in football, basketball, and other sports that require repeated use of the leg and knee. 

Signs & Symptoms

The ACL may tear suddenly and without warning when an individual decelerates, cuts to the side, or lands awkwardly. Symptoms of a torn ACL include:

  • A popping sound
  • Your knee giving out from under you
  • Pain and swelling, including tenderness around the joint
  • Reduced range of motion in the knee
  • Pain or discomfort when walking


The best time to diagnose an acute ACL tear is within the first hour after injury, before the knee swells, but this is not always possible. The initial evaluation includes a complete history of the injury — how it happened, whether the knee was hyperextended or other aspects of the “mechanism” of injury, whether the individual heard a pop, where and how badly the knee hurts, and whether the knee feels unstable — as well as details of previous knee injuries.

Once a thorough history is obtained, the physician performs a physical exam of the knee to assess the stability of the ligaments. Using specific tests, the physician can diagnose ACL injuries by applying forces to the knee and feeling for abnormal motion. Obtaining additional studies, such as x-rays and an MRI, can be very helpful to give an accurate picture of the extent of the injury.


Treatment may be nonsurgical or surgical, depending on the patient’s desired lifestyle. The question is not so much the patient’s level of activity in the past, but the expectations for the future. If a patient’s goal is to continue an active lifestyle, surgery may be the treatment of choice because a torn ACL does not heal.

Nonsurgical therapy consists of a period of protective bracing with progressive return to range of motion and muscle-strengthening exercises. The goal is to create natural stability for the knee by developing the quadriceps and hamstring muscles.


Several prevention programs have been developed in an attempt to decrease the incidence of ACL injuries. The focus of current prevention programs is on proper nerve and muscle control of the knee. These programs focus on plyometrics, balance, and strengthening and stability exercises for the lower limbs.


The goals of rehabilitation are to restore range of motion and to strengthen the quadriceps and hamstring muscles, which help stabilize the knee. Precautions you can take at home for minor ACL injuries include:

  • Reduce activity during the acute phase.
  • Ice the injury multiple times per day.
  • Compress the knee with a bandage or wrap.
  • Elevate the knee above the level of the heart.
  • Use anti-inflammatory medications such as ibuprofen to reduce inflammation and speed up recovery.

Rehabilitation Exercises

  • Quad sets: Sit with legs extended and fully contract the muscles of the front thighs. Hold contractions for 10 seconds. Repeat 10 times for three sets.
  • Straight leg raises (hip flexion): Lie with one leg extended and the other bent at the knee. Lift the entire leg from the hip so that the heel is about five inches above the floor. Hold this position for five to 10 seconds and then slowly lower the leg. Repeat 10 times for three sets.
  • Backward leg raise (hip extension): Lie on stomach with legs straight. Lift one leg as high as possible and hold for five to 10 seconds and then slowly lower the leg. Repeat 10 times for three sets.
  • Hip abduction: Lie on side of uninjured leg, so that the injured leg is on top of the uninjured leg. Lift the injured leg at the hip away from the body. Lift the leg as high as possible and hold for five to 10 seconds, then slowly lower the leg. Repeat 10 times for three sets.
  • Hip adduction: Lie on side of injured leg, with uninjured leg bent at the knee and foot flat on the floor. Lift the injured leg at the hip toward the other leg. Hold for five to 10 seconds and then slowly lower the leg. Repeat 10 times for three sets.
  • Half-knee bends: Stand with feet shoulder-width apart. Slowly lower the body weight by bending the knees. Do not perform a full squat, but rather stop at about half of the full squat position and then fully extend the knees. If there is pain before achieving the half-squat position, stop downward travel at that point. Repeat 10 times for three sets.
Content on this page is for informational purposes only. If injured, please consult a physician.

Contact Us

To schedule an appointment with a physician or other Sports Medicine expert, call
1-855-93-SPORT (77678).

UPMC Rooney
Sports Complex
3200 S. Water St.
Pittsburgh, PA 15203

UPMC Lemieux Sports Complex
8000 Cranberry Springs Drive
Cranberry Township, PA 16066

A short video series developed in partnership with ROOT Sports and geared toward the athlete in all of us.

UPMC HealthBeat - visit our blog to learn more. 

©  UPMC | Affiliated with the University of Pittsburgh Schools of the Health Sciences
Supplemental content provided by Healthwise, Incorporated. To learn more, visit

For help in finding a doctor or health service that suits your needs, call the UPMC Referral Service at 412-647-UPMC (8762) or 1-800-533-UPMC (8762). Select option 1.

UPMC is an equal opportunity employer. UPMC policy prohibits discrimination or harassment on the basis of race, color, religion, ancestry, national origin, age, sex, genetics, sexual orientation, gender identity, marital status, familial status, disability, veteran status, or any other legally protected group status. Further, UPMC will continue to support and promote equal employment opportunity, human dignity, and racial, ethnic, and cultural diversity. This policy applies to admissions, employment, and access to and treatment in UPMC programs and activities. This commitment is made by UPMC in accordance with federal, state, and/or local laws and regulations.

Medical information made available on is not intended to be used as a substitute for professional medical advice, diagnosis, or treatment. You should not rely entirely on this information for your health care needs. Ask your own doctor or health care provider any specific medical questions that you have. Further, is not a tool to be used in the case of an emergency. If an emergency arises, you should seek appropriate emergency medical services.

For UPMC Mercy Patients: As a Catholic hospital, UPMC Mercy abides by the Ethical and Religious Directives for Catholic Health Care Services, as determined by the United States Conference of Catholic Bishops. As such, UPMC Mercy neither endorses nor provides medical practices and/or procedures that contradict the moral teachings of the Roman Catholic Church.

Pittsburgh, PA, USA