The anterior cruciate ligament (ACL) is in the middle of the knee and keeps the tibia from shifting forward, relative to the femur. The ACL can be partially torn (sprained) or completely torn (ruptured).


Sports related causes.

ACL injuries can occur with planting foot on the ground from jump, rapidly changing direction, or from a direct injury to the leg with a planted foot. They are common with soccer, volleyball, basketball, football, and skiing but can be seen in any sport.

Other causes of ACL injuries

Even minor injuries can occasionally result in tears of the ACL when the force if just right - from walking down a step to standing up from a chair.


With sports injuries, people often hear a popping noise and sensation followed by knee swelling, instability, and pain. When the injury is minor, they may feel ill, with limited knee pain and a sense of knee instability or loss of range of motion.


A physical exam by a doctor is performed to determine if the tibia maintains a normal relationship with the femur during stress (Lachman test and pivot shift tests). Knee pain with movements, swelling, and tenderness may also be present. MRI to see any damage to ligaments, tendons, muscles, and knee cartilage.

If the physical exam in inconclusive, then an MRI is warranted to evaluate the integrity of the ACL and evaluate for other causes of knee pain.

Injury grades

Doctors use a grade to indicate the severity of the ACL injury.

  • Grade 1: Low grade stretching injury/sprain.
  • Grade 2: Partial tear/sprain with weak, stretched ligament providing reduced function.
  • Grade 3: Complete or near complete tear (rupture) with lost function.


Treatment plans depend on the severity of injury, patient age, and the activity level of the patient.

After the initial injury, icing, elevation, ace bandaging, and anti-inflammatory medicines are recommended.

Grade 1 or 2 injuries: Braces and physical therapy will help support while strengthening the muscles and allowing the ACL to heal.

Grade 3 injury in young and athletic patients

An ACL rupture will not heal so surgery is often advised for young or active patients who want to recover full function. A new ACL can be placed surgically using another one of the patient's ligaments (autograft) or a ligament from a cadaver (allograft). After surgery, a thorough physical therapy regiment is critical to healing and recovering function.

Grade 3 injury older, nonathletic patients

Older patients who do not require ACL stability for sports or other high level activities may be advised to avoid surgery, be conscientious about their activities, and strengthen the knee muscles.