ACL injury
DEFINITION
At Mayo Clinic, we take the time to listen, to find answers and to provide you the best care.
Learn more. Request an appointment.
An ACL injury is the tearing of the anterior cruciate (KROO-she-ate) ligament, or ACL, inside your knee joint. An ACL injury most commonly occurs during sports that involve sudden stops and changes in direction — such as basketball, soccer, tennis and volleyball.
Immediately after an ACL injury, your knee may swell, feel unstable and become too painful to bear weight. Many people hear or feel a “pop” in their knee when an ACL injury occurs.
Depending on the severity of your ACL injury, treatment may include surgery to replace the torn ligament followed by rehabilitation exercises to help you regain strength and stability. If your favorite sport involves pivoting or jumping, a proper training program may help reduce your chances of an ACL injury.
CAUSES
Ligaments are strong bands of tissue that connect one bone to another. The ACL, one of two ligaments that cross in the middle of the knee, connects your thighbone (femur) to your shinbone (tibia) and helps stabilize your knee joint.
Most ACL injuries happen during sports and fitness activities. The ligament may tear when you slow down suddenly to change direction or pivot with your foot firmly planted, twisting or hyperextending your knee.
Landing awkwardly from a jump can also injure your ACL, as can falls during downhill skiing. A football tackle or motor vehicle accident also can cause an ACL injury. However, most ACL injuries occur without such contact.
SYMPTOMS
At the time of an ACL injury, signs and symptoms may include:
- A loud “pop” sound
- Severe pain and inability to continue activity
- Knee swelling that usually worsens for hours after the injury occurs
- A feeling of instability or “giving way” with weight bearing
When to see a doctor
Most people seek immediate medical attention after an ACL injury.
