Torn ACL

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What is a torn ACL?

The ACL—the anterior cruciate ligament—is one of four main ligaments in your knee. Ligaments are tough connective tissues that help hold joints together or bones and cartilage together. The ACL is found in the middle of your knee. Its role is to prevent your shin bone from moving in front of your thigh bone.

Torn ACLs are one of the most common knee injuries, especially among athletes who play sports like football, soccer and basketball. There are as many as 200,000 torn ACLs each year in the United States and women are four to six times more likely than men to have an ACL injury. You can have a partially torn ACL or a complete tear.

ACL tears should be treated as quickly as possible to reduce the risk of further damage. If you experience ACL injury symptoms, which usually appear as the injury occurs, see your doctor as soon as possible. You should avoid putting weight on your injured knee until it has been checked by a medical professional. Torn ACL recovery depends on the extent of damage to the ligament and whether or not surgery is necessary to reconstruct it.

What are the symptoms of a torn ACL?

ACL injury symptoms usually appear as soon as the injury occurs. If the tear is minor, symptoms may come on gradually if the tear worsens over time.

Common ACL tear symptoms include:

  • Popping sound when the injury occurs

  • Pain in the knee, especially when putting weight on it

  • Swelling, which may appear a few hours after the injury

  • Difficulty moving your knee and limited range of motion

  • Feeling that your knee is moving in a strange way or is unstable 

A torn ACL can be a serious injury with lasting effects. If you suspect a serious ACL injury, don’t put weight on your knee because the force can worsen the ACL tear making it more difficult to heal properly. If you are unable to move to a vehicle without risking further damage to your knee, you may need to call 911 for medical assistance. A doctor will perform an ACL tear test to evaluate the ligament, ask you about typical torn ACL symptoms and your activity at the time of injury, and may order MRI (magnetic resonance imaging) of your knee to confirm the diagnosis. 

What causes a torn ACL?

A torn ACL is a common sports injury, particularly related to activities that put pressure or strain on your knee. Forceful actions that cause ACL tears include:

  • Changing direction very suddenly while running

  • Pivoting or turning your body while one foot remains firmly on the ground

  • Suddenly stopping while moving at a rapid speed

  • Landing badly from a jump

  • Receiving a direct hit to the knee

You don’t need to be an athlete to tear your ACL. The causes listed above could occur during every day activities, such as suddenly changing directions while running for the bus, slipping on a wet floor, or being in a car accident.

What are the risk factors for a torn ACL?

The most common risk factor for any ACL injury including an ACL tear is participating in a sport or activity that puts pressure on your knee. If you have already had a torn ACL, you are also at higher risk for tearing it again, particularly if you are a woman. Women tend to injure their ACL more often than men. While men tend to have stronger hamstrings than quadriceps, it is the opposite for women. The stronger quadriceps can pull on the ACL, making it more susceptible to damage.

Reducing your risk of a torn ACL

You may be able to lower your risk of a torn ACL by:

  • Warming up and stretching before the activity

  • Strengthening your core muscles

  • Strengthening the muscles around your knees

  • Practicing landing jumps safely

  • Practicing pivoting in safe manner

  • Working on balance training, which helps you avoid some movements that increase the risk of injuring your knee

Speak with your coach or trainer about proper body mechanics and exercises you can do to reduce your risk of injury. If you experience any pain in your knee following a hard fall, landing, or even twisting motion, see your doctor. Checking your knee for signs of damage allows for early treatment if necessary.

How is a torn ACL treated?

The initial treatment for ACL tears is to immobilize your knee and manage the pain and swelling. Follow the RICE method:

Rest: Do not bear weight on your knee.

Ice: Apply ice packs to your knee for 20 minutes at a time, at least every two hours.

Compression: Apply a compression bandage around your knee, but do not make it so tight as to affect blood circulation to the rest of your leg.

Elevation: Elevate your leg.

Whether you need ACL surgery to repair the tear depends on your situation and the extent of the injury. There may be additional knee damage to repair with a full ACL tear. Athletes and those with active lifestyles often have surgery, while those with a more sedentary lifestyle may not.

Physical therapy may be sufficient for people with partial tears and no other damage, or for people who do not usually put a lot of stress on their knee. A physical therapist will help you exercise your leg so the muscles can help support your knee. You may need to wear a knee brace when participating in certain types of activities to help protect it from further damage. Without surgery, ACL tear recovery and rehabilitation time is approximately three months for a partial tear.

Surgery may be the right option for you if: you are an athlete, you participate in activities that require you to jump or pivot, or you do heavy manual labor. The surgery is an ACL reconstruction rather than an ACL repair. Studies have shown that repairs do not hold up as well as reconstruction. Using a procedure called arthroscopy, your orthopedic surgeon makes tiny incisions into your knee. A camera is inserted into your knee through one of the incisions and the instruments to repair the tear are inserted through the other incisions.

After removing the torn ligament, the surgeon takes tissue from another part of your body—usually the main patellar tendon or hamstring—and attaches it to the bone. Sometimes, the grafted tissue comes from another person. After surgery, you will need rehabilitation therapy and physical therapy to regain full use of your knee. It can take up to a year for torn ACL recovery after surgery.

What are the potential complications of a torn ACL?

Left untreated, a torn ACL may result in an unstable knee—one that feels like it’s not quite right, or like it’s moving or popping while you are walking. However, partial tears do usually heal well without surgery as long as there is not a lot of strain on the knee. Continued strength training and conditioning prior to at-risk activities will help prevent future injuries.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Aug 21
  1. ACL Injury: Does It Require Surgery? American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=a00297
  2. Anterior Cruciate Ligament (ACL) Injuries. American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=a00549
  3. ACL Reconstruction. MedlinePlus, U.S. National Library of Medicine. https://medlineplus.gov/ency/article/007208.htm
  4. Osborn M. Why Do Females Injure Their Knees Four to Six Times More Than Men...And What Can You Do About It? University of Colorado Hospital. 2012. http://www.ucdenver.edu/academics/colleges/medicalschool/departments/Orthopaedics/clinicalservices/sportsmed/Documents/WISH_SPORTSMED_Female%20Knee%20Injuries%20and%20ACL.pdf
  5. Smith HC, Vacek P, Johnson RJ, et al. Risk Factors for Anterior Cruciate Ligament Injury: A Review of the Literature — Part 1: Neuromuscular and Anatomic Risk. Sports Health. 2012;4(1):69-78. doi:10.1177/1941738111428281. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3435896/
  6. ACL Injury. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/acl-injury/symptoms-causes/syc-20350738
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