A ligament is a band of tissue that connects a bone to another bone. The anterior cruciate ligament (ACL) is located inside your knee joint and connects the bones of your upper and lower leg.
An ACL injury occurs when the ligament is stretched or torn. A partial ACL tear occurs when only part of the ligament is torn. A complete ACL tear occurs when the entire ligament is torn into two pieces or detaches from the bone.
More About Your Injury
The ACL is one of several ligaments that keep your knee stable. It helps keep your leg bones in place and allows your knee to move back and forth.
An ACL injury can occur if you:
- Get hit very hard on the side of your knee, such as during a football tackle
- Twist your knee
- Quickly stop moving and change direction while running, landing from a jump, or turning
- Land awkwardly after jumping
Skiers and people who play basketball, football, or soccer are more likely to have this type of injury. Women are more likely to tear their ACL than men when they participate in sports.
What to Expect
It is common to hear a "popping" sound when an ACL injury occurs. You also may have:
- Knee swelling that occurs within a few hours of injury
- Knee pain, especially when you try to put weight on the injured leg\
- Knee instability when you start putting weight on it
If you have a mild injury, you may notice that your knee feels unstable or seems to "give way" when using it. ACL injuries often occur along with other knee injuries, such as to the cartilage called the meniscus. These injuries also may need to be treated, sometimes with surgery.
After examining your knee, your health care provider may order these imaging tests:
- X-rays to check for damage to the bones in your knee.
- An MRI of the knee. An MRI machine takes special pictures of the tissues inside your knee. The pictures will show whether these tissues have been stretched or torn.
If you have an ACL injury, you may need:
- Crutches to walk until the swelling and pain get better
- A brace to support and stabilize your knee
- Physical therapy to help improve joint motion and leg strength
- Surgery to reconstruct the ACL and other structures that also may have been injured
Some people can live and function normally with a torn ACL. However, most people feel like their knee is unstable and may "give out" with more rigorous activities. Most people will have the ACL reconstructed in order to return to their previous activities. Unrepaired ACL tears can lead to further knee damage, especially to the meniscus.
Self-care at Home
Follow R.I.C.E. to help reduce pain and swelling:
- Rest your leg. Avoid putting weight on it.
- Ice your knee for 20 minutes at a time 3 to 4 times a day. Do not apply ice directly to your skin. Wrap the ice in a clean cloth first.
- Compress the area by wrapping it with an elastic bandage or compression wrap.
- Elevate your leg by raising it above the level of your heart.
You can use ibuprofen (Advil, Motrin), or naproxen (Aleve, Naprosyn) to reduce pain and swelling. Acetaminophen (Tylenol) helps with pain, but not with swelling. You can buy these pain medicines at the store.
- Talk with your provider before using pain medicines if you have heart disease, high blood pressure, kidney disease, or have had stomach ulcers or internal bleeding in the past.
- Do not take more than the amount recommended on the bottle or by your provider.
After your injury, you should not play sports or do other strenuous activities until you and your provider decide what treatment is best for you.
If you have surgery to reconstruct your ACL:
- Follow instructions on self-care at home.
- You will need physical therapy to regain the full use of your knee.
- Your recovery after surgery can take about 6 months. But you should be able to do the same activities you did before.
If you do not have surgery:
- You will need to work with a physical therapist to lessen swelling and pain and regain enough range of motion and strength in your leg to resume activity. This may take a few months.
- Depending on your injury, you may not be able to do certain types of activities that could re-injure your knee.
When to Call the Doctor
Contact your provider if you have any of the following:
- Increase in swelling or pain
- Self-care does not seem to help
- You lose feeling in your foot
- Your foot or leg feels cold or changes color
- Your knee suddenly locks and you can't straighten it
If you have surgery, contact your surgeon if you have:
- A fever of 100°F (38°C) or higher
- Drainage from the incisions
- Bleeding that won't stop
Cruciate ligament injury - aftercare; ACL injury - aftercare; Knee injury - anterior cruciate
Lamplot JD, Bogunovic L, Wright RW. Revision anterior cruciate ligament injuries. In: Miller MD, Thompson SR, eds. DeLee, Drez, & Miller's Orthopaedic Sports Medicine. 5th ed. Philadelphia, PA: Elsevier; 2020:chap 99.
Miller RH, Azar FM. Knee Injuries. In: Azar FM, Beaty JH, eds. Campbell's Operative Orthopaedics. 14th ed. Philadelphia, PA: Elsevier; 2021:chap 45.
Members of the Writing, Review, and Voting Panels of the AUC on Prevention and Treatment of Anterior Cruciate Ligament Injuries, Quinn RH, Saunders JO, et al. The American Academy of Orthopaedic Surgeons appropriate use criteria on the management of anterior cruciate ligament injuries. J Bone Joint Surg Am. 2016;98(2):153-155. PMID: 26791036 pubmed.ncbi.nlm.nih.gov/26791036/.
Review Date 4/24/2023
Updated by: C. Benjamin Ma, MD, Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.