What is an ACL Injury?

An ACL injury is a tear or sprain of the anterior cruciate (KROO-she-ate) ligament (ACL) — one of the major ligaments in your knee. ACL injuries most commonly occur during sports that involve sudden stops or changes in direction, jumping and landing — such as soccer, basketball, football and downhill skiing.

What happens?

Many people hear or feel a “pop” in the knee when an ACL injury occurs. Your knee may swell, feel unstable and become too painful to bear weight.

Depending on the severity of your ACL injury, treatment may include rest and rehabilitation exercises to help you regain strength and stability or surgery to replace the torn ligament followed by rehabilitation. A proper training program may help reduce the risk of an ACL injury.


A loud “pop” or a “popping” sensation in the knee
Severe pain and inability to continue the activity
Rapid swelling
Loss of range of motion
A feeling of instability or “giving way” with weight bearing

When to see a doctor

Seek immediate care if any injury to your knee causes signs or symptoms of an ACL injury. The knee joint is a complex structure of bones, ligaments, tendons and other tissues that work together. It’s important to get a prompt and accurate diagnosis to determine the severity of the injury and get proper treatment.


Can happen when:
Suddenly slowing down and changing direction (cutting)
Pivoting with your foot firmly planted
Landing awkwardly from a jump
Stopping suddenly
Receiving a direct blow to the knee or collision, such as a football tackle

Risk Factors

Participating in certain sports, such as soccer, football, basketball, gymnastics and downhill skiing
Poor conditioning
Wearing footwear that doesn’t fit properly
Using poorly maintained sports equipment, such as ski bindings that aren’t adjusted properly
Playing on artificial turf surfaces


Exercises that strengthen leg muscles, particularly hamstring exercises, to ensure an overall balance in leg muscle strength
Exercises to strengthen the core, including the hips, pelvis and lower abdomen
Training and exercise emphasizing proper technique and knee position when jumping and landing from jumps
Training to improve technique when performing pivoting and cutting movements

Treetment and Recovery

Rest. General rest is necessary for healing and limits weight bearing on your knee.
Ice. When you’re awake, try to ice your knee at least every two hours for 20 minutes at a time.
Compression. Wrap an elastic bandage or compression wrap around your knee.
Elevation. Lie down with your knee propped up on pillows.


Medical treatment for an ACL injury begins with several weeks of rehabilitative therapy. A physical therapist will teach you how to do exercises that you will perform either with continued supervision or at home. You may also wear a brace to stabilize your knee and use crutches for a while to avoid putting weight on your knee.

The goal of rehabilitation is to reduce pain and swelling, restore your knee’s full range of motion, and strengthen muscles. This course of physical therapy may successfully treat an ACL injury for individuals who are relatively inactive, engage in moderate exercise and recreational activities, or play sports that put less stress on the knees.


Your doctor may recommend surgery if:

You’re an athlete and want to continue in your sport, especially if the sport involves jumping, cutting or pivoting
More than one ligament or the meniscus in your knee is also injured
The injury is causing your knee to buckle during everyday activities
During ACL reconstruction, the surgeon removes the damaged ligament and replaces it with a segment of tendon — tissue similar to a ligament that connects muscle to bone. This replacement tissue is called a graft.