What is the ACL?

The ACL is the anterior cruciate ligament of the knee.  Its main purpose is a knee stabilizer to prevent the knee during rotation, bending and straightening.  The ACL is a ligament that runs from the femur to the tibia- thigh bone to shin bone- within the knee joint. 
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On the left we see a normal ACL. On the right, the arrow highlights where the ACL is torn.

How do I know if my ACL is torn?

Most ACL tears occur during a non contact injury.  Most people have a bent knee with the foot planted and then rotate through the knee.  They usually here a pop and struggle to put weight on the knee.  Over 75% of the time, the knee joint swells up within 24 hours.  It becomes difficult to bend the knee and it becomes difficult to put pressure on the knee due to swelling.  Usually, if a trainer or phyisican is present, they will try to examine you in the moments after the injury as the examination for an ACL tear becomes more difficult if the knee swells.  After initial physical exam, an MRI is warranted to see if the ACL is torn and to see if there is any additional cartilage damage. 
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A swollen knee can be seen on the right. This usually occurs within 24 hours of an ACL tear.
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The typical position of injury when there is a non-contact ACL injury

What does the MRI show?

The MRI will show the tear of the ligament and any additional soft tissue damage associated with the tear.  More commonly than not, the meniscus is also torn during the ACL tear.  The MRI also usually shows bone edema, a "black and blue mark" in the knee. in two classic locations. 
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The picture on the left shows the fibers running between the bones of the knee. The figure on the right shows how the ligaments are no longer present, indicating an ACL tear.
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The red lines demonstrate the normal course of where the ACL should be. There should be fibers in this location but they are completely torn.
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This photo shows the bone bruises associated with an ACL tear. If these bruises are present, there is a very high chance an ACL tear is present.

How do we treat ACL Tears?

Patient treatment depends on a variety of factors including age, activity level and demands from the knee.   Most people report instability, which is the indication for surgery.  With an unstable knee, patients report buckling and giving out, especially when performing cutting sports.  All of our surgeons do arthroscopic ACL reconstruction.

Rehabilitation

Probably the most difficult part of ACL Reconstruction is the rehabilitation process.  The process requires regaining leg strength and motion as well as instilling confidence.  6-12 months is the time frame to return to sport, depending on a variety of factors, like meniscus tears, which can delay return to sport time.  ACL injuries require extensive rehabilitation and strengthening.  Return to sport is generally not recommended until the operative (repaired) ACL-sided muscles of the quadriceps are at 90% of the non-operative side.

Learn more from the American Academy of Orthopaedic Surgeons

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