An ACL injury is the tearing 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, jumping or changes in direction — such as basketball, soccer, football, tennis, downhill skiing, volleyball and gymnastics.
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.