Damage to the ACL ligament is one of the most frequent and serious knee injuries in sports. The ACL may be completely torn into two pieces or only partially torn. The person injured is usually unable to resume activities.

ACL damage may exhibit certain typical symptoms:

• A popping or snapping sensation in the knee at the time of injury.
• Motion restrictions, make it difficult to flex or properly extend the knee.
• Unable to continue walking or exercising because the knee joints turn loose.
• Visible knee swelling six hours after the injury.
• The knee feels shaky and gives away.

Some common causes of an injury:

• Running at a fast pace and suddenly stopping.
• While sprinting, abruptly change your course, twisting your knee.
• Rapid braking and direction change.
• If a strong side impact strikes your knee.
• Extending your knee too far.
• Sustaining a direct knee strike or colliding with another object on the side, such as during a football tackle.

• If you play sports, you should pay special attention to two factors, how you land after a jump and how you take hard, rapid steps to speed in another direction.
• A series of stretching and warming-up exercises as well as injury-reduction jumping drills like jumping and landing drills may help.
• Leg strengthening activities, especially hamstring workouts, to maintain a balance in leg muscle strength.
• To prevent injuries, wear padding and shoes that are appropriate for your sport and fits you well.