Anterior Cruciate Ligament (ACL) tear

Anterior Cruciate Ligament (ACL) tear of the knee

Diagnosis: Anterior Cruciate Ligament (ACL) tear of the knee

Clinical Keywords: Knee injury, ACL tear, twisting

1. Common athletic injury usually associated with with a powerful pivoting movement such as a sudden change of direction while your foot is planted on the ground or landing from a jump with a straight leg
2. An unrepaired ACL tear leaves the knee prone to recurrent injury episodes 
3. ACL tears are often associated with other injuries in the knee
4. Over time, ACL tears are associated with earlier development of degenerative arthritis in the knee

Description:

The ACL (or anterior cruciate ligament) is a structure in the middle of the knee joint that connects the back of the femur bone to the front of the tibia bone.  The orientation of the ACL limits the ability of the tibia bone to slide forward, keeping it aligned with the femur bone.  When a strong force moves the tibia forward, the ACL gets stretched and then torn.  Usually this force comes from the strong muscles of the front of the thigh, the quadriceps muscle, such as when an athlete plants their foot to suddenly change direction or lands from a jump on a straight leg.  This force can also occur in a sport like football in which the back of the lower leg is contacted and pushed forward suddenly.

An ACL can be diagnosed by the history of the injury and physical examination which can demonstrate the tibia shifting forward which indicated a tear of the ligament. 

ACL injuries are often associated with injuries to other structures in the knee.  Common associated injuries include meniscus tears, injury of the MCL (medial collateral ligament), bone bruises and cartilage injuries.  An MRI is often obtained with suspected ACL tear to both confirm the diagnosis and also to look for associated injuries.

Once the ACL is completely torn, it generally does not heal well enough to restore stability of the knee and this can lead to repeated injuries of the knee unless either the ligament is fixed or the athlete avoids activities that are likely to result in these episodes.

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