What Does It Mean To Tear Your ACL?
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Medically reviewed by Oluseun Olufade, MD
Tearing your anterior cruciate ligament (ACL) means you have torn the tissue in the middle of your knee that connects your thigh bone (femur) and shinbone (tibia).
The ACL is one of four main ligaments in your knee. A ligament is a band of tissue that connects two bones. The ACL and another ligament cross each other like an X, with the ACL being the ligament that's closer to the front of your knee.
When the ACL functions correctly, it stabilizes your knee joint by preventing your shinbone from jutting in front of the thigh bone. Your ACL also helps prevent overbending or rotating your knee.
When you tear your ACL either partially or completely, you lose full function of your ACL. Without full ACL function, people often can't play sports or do other physical activities at the level they played before the injury. Most people with ACL tears deal with unstable knees that "give out" when they walk or run, which can increase the risk of more knee damage.
Here's what happens when you have an ACL tear and what to expect if the injury happens to you.
How Do You Tear Your ACL?
Any motion that forcefully twists or stretches the ACL can cause a tear. A partial ACL tear rips a section of the ligament. A complete ACL tear rips the ligament into two pieces or detaches the ligament from the thigh bone or shinbone. The most common ACL tears happen in the center of the ligament or when the ACL is pulled off the thigh bone.
People often get ACL tears from playing sports like basketball, soccer, and football or by skiing. Some specific ways you can tear your ACL include:
Experiencing a forceful hit or impact to the side of the knee
Overextending or twisting the knee joint
Quickly stopping and changing direction while running or landing a jump
Awkwardly stopping or landing a jump
Female athletes are more at risk for ACL tears. Research shows women tear their ACL two to eight times more than men. Female bodies often have less muscle mass around the knee and more range of motion that can contribute to knee instability—increasing the risk of an ACL tear.
Symptoms of Tearing Your ACL
An ACL tear can make your knee feel weak and unstable, often causing knee pain when you try to stand or walk. When you first tear your ACL, you may hear a popping sound. Within a few hours of tearing your ACL, the knee will start to swell.
People with partial ACL tears can often walk but deal with instability and the knee "giving out." Despite being a less damaging injury, partial tears are often more painful than complete tears. If you completely tear your ACL, you may be unable to:
Stand and put weight on your knee
Jump and land
Accelerate and change directions when walking or running
Quickly pivot on the knee
In rare cases, some people with a torn ACL can still move somewhat normally.
What to Do if You Think You've Torn Your ACL
See your healthcare provider if you believe you've torn your ACL. They can refer you to a specialist like an orthopedist—a healthcare provider who treats skeletal and muscular injuries—or a sports medicine provider.
You should not go back to playing or participating in physical activity until after you've been checked out and treated. Until you see a healthcare provider, try to keep your knee straight with a splint.
As you wait for your appointment, tou should also take care to avoid further damage and manage pain by:
Keeping weight off your injured leg
Elevating your injured leg
Applying ice to decrease inflammation and pain
Taking nonsteroidal anti-inflammatory drugs (NSAIDs) like Advil (ibuprofen) for pain and inflammation
Seek emergency medical attention if your foot feels cold and looks blue after you injure your knee. These are signs of a medical emergency where the knee is dislocated, and the blood vessels are damaged.
How Is an ACL Tear Diagnosed?
An orthopedist or sports medicine provider will ask you about your symptoms and do a physical exam. If an ACL tear is suspected, they might order magnetic resonance imaging (MRI) tests to confirm the degree of your ACL tear.
A knee MRI scan uses strong magnets to take detailed 3D images of the knee joint, muscles, and tissues to see where the ACL is torn. During the scan, you'll lie on a table that enters a tunnel-like scanner. You'll stay still in the scanner for 30-60 minutes. Sometimes the radiologist who performs the scan will insert a special dye (contrast) into the knee joint to see the area more clearly.
Besides determining where and how severe the tear is, the MRI can also show if you've damaged other parts of the knee. Nearly half of injuries that tear the ACL also damage other knee ligaments, the meniscus (C-shaped, cushioning cartilage between the shin and bones), or articular cartilage (smooth cartilage on the ends of bones).
Since other knee joint injuries often accompany an ACL tear, your healthcare provider may also order a knee X-ray. Sending individual X-ray waves through the knee can help take images of the bones in the knee to see if you've damaged any bone.
How Is an ACL Tear Treated?
Torn ACL treatment typically involves a mixture of rest, rehabilitation, and surgery. Most people who tear their ACL will also need crutches to help them walk or a brace for knee stabilization. Partial tears are typically treated without surgery, but complete tears cannot heal independently and need surgery to replace the ligament.
R.I.C.E.
People with minor ACL tears can help reduce pain and swelling at home as the ligament heals. Someone waiting for surgery can also benefit from rest to avoid further injury. After an ACL tear, your healthcare provider may suggest R.I.C.E. (rest, ice, compress, and elevate) to help reduce pain and swelling. Following R.I.C.E. with an ACL tear includes:
Resting and avoiding putting weight on the injured leg, such as by using crutches
Icing the knee three to four times a day for 20 minutes
Compressing the injured knee in a compression wrap or bandage
Elevating the leg of the injured knee
Your provider may also recommend taking over-the-counter medications like Advil (ibuprofen) or Aleve (naproxen) to help with pain and inflammation.
Surgery
ACL tears are not usually repaired with stitches because the ligament would eventually tear again. Instead, people have complete ACL reconstruction surgery using new tissue. ACL reconstruction is the best option for a younger, more active person or an athlete who wants to return to sports activities after a complete ACL tear. A surgeon usually replaces a torn ACL with ligaments or thin muscle taken from either you or a donor (a person who has died).
During surgery, a surgeon will make small cuts around the knee to insert medical instruments and knee arthroscopy (a tiny camera inserted into the knee to better see the damage). The torn ACL is removed, and the surgeon makes holes in your bone for the ACL replacement tissue. The new ACL will be secured with screws or other medical devices. Then, your knee will be stitched up and bandaged.
After surgery, you'll have to wear a knee brace for one to six weeks while the new tissue heals to form a new ACL. You may also need crutches during that time.
Physical Therapy
Physical therapy helps you regain strength and range of motion in your knee after tearing your ACL. People who have partially torn the ACL and do not need surgery often go to physical therapy for a few months. Physical therapy after ACL surgery can last for four to six months—or up to 12 months if you're trying to return to sports like soccer or basketball.
During physical therapy, you will do exercises that help you put weight back onto your injured leg. You will also strengthen surrounding muscles to help you move and prevent future ACL tears. Activities that move the knee will also help improve your range of motion post-surgery.
How Long Does an ACL Tear Take To Heal?
Depending on the severity of your injury, an ACL tear can take three months to a year to heal. A partially torn ACL typically recovers after at least three months of recovery and physical therapy. Most people will regain full function after a partial ACL tear recovers. However, some people will still experience knee instability issues.
Complete ACL tears that require surgery and rehabilitation take at least 9 months to heal. Athletes and people trying to return to a sport that caused their ACL tear may need up to a year to fully heal. After your ACL heals and you strengthen the tendon and surrounding muscles, you should be able to return to your normal activity levels.
If you don't have surgery to repair a completely torn ACL, you may be unable to play sports requiring a lot of pivoting. You may also still experience instability issues when walking. People who continue to deal with chronic knee instability can increase their risk of damaging their meniscus and knee cartilage 10 or more years after an ACL injury.
How to Prevent an ACL Tear
Learning how to move and land on the knee joint properly during sports can help reduce your risk of an ACL tear. To help athletes prevent ACL tears, coaches and athletic trainers will often teach exercises that:
Strengthen the muscles around the knee joint for more stability
Help athletes land safely when they fall
Help athletes use proper knee position when jumping or landing
Correct one-leg landings, out-of-control baseline landings, or straight-leg landings
Improve the angle and force on the knee by changing foot movements when pivoting or suddenly changing direction
Some people may use a knee brace during sports to help prevent knee injuries like an ACL tear. However, research shows that preventative knee braces don't reduce knee injuries. Research also indicates wearing a knee brace to avoid an ACL re-reupture doesn't reduce your chance of reinjury after ACL reconstruction.
Quick Review
A torn ACL is a common sports injury caused by overrotating or stretching the anterior cruciate ligament. This is connective tissue in the middle of your knee that bands together the thigh bone and shinbone and supports the knee joint. When you tear your ACL, you may experience knee pain and hear a popping sound. Following the injury, you may have knee instability, making it hard to put weight on or walk on your injured leg.
Partial tears often require rest and physical therapy. Complete tears will need surgery to replace the ACL. After your ACL is repaired and you complete months of physical therapy, you can typically return to your physical activities and sports. However, some people will still have issues with knee instability after ACL treatment.
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