What is an ACL Injury?
The anterior cruciate ligament, or ACL, is the most important ligament of the knee to prevent the knee from sliding forward or rotating anterolaterally. Patients who sustain an ACL tear often have problems with twisting and turning activities, such as in playing football, soccer, or skiing, and will often require an ACL reconstruction to provide stability to their knee.
In addition to its stability role in the knee, the ACL also provides protection for the menisci of the knee. When the knee continues to have instability episodes, it is not uncommon to have either the medial or lateral meniscus tear. However, when menisci tear there is much higher risk of the development of osteoarthritis. Because of this, Dr. LaPrade usually recommends ACL surgery and that an ACL reconstruction be performed in young or otherwise active patients and in almost all patients who report instability with twisting or turning activities.
An ACL injury is classified by the amount of injury to the ligament:
• Grade I: a partial ACL tear
• Grade II: near complete ACL tear
• Grade III: a complete ACL tear – the ligament is non-functional
Depending on the patient’s age, activity level and grade of tear will determine the correct treatment option.
Description of ACL Reconstruction
An ACL surgery requires precise knowledge of the anatomy of the knee, attachment sites of the ACL and knowledge on the other ligaments and structures of the knee. If one fails to replace an anterior cruciate ligament at its correct attachment sites or if other concurrent injuries are not treated, there is a much higher risk of failure of the ACL graft.
While there are two bundles of the ACL, the anteromedial and posterolateral bundles, there is still controversy as to whether both should be reconstructed as a single ligament or as two separate ligament grafts. While the double-bundle ACL reconstruction technique appeared very promising initially, many research groups, including ours, have significantly narrowed the indications for double-bundle ACL surgery and found there is very little difference between a single and double-bundle ACL reconstruction for the vast majority of patients.
The most important technical issue is to have the ACL reconstruction graft placed in the correct position. On the tibia (shinbone), the tunnels should be in line with the posterior margin of the anterior horn of the lateral meniscus. On the femur (thigh bone), the reconstruction tunnel should be placed at the midpoint of the attachment bundles of the anteromedial and posterolateral bundles, with the main portion of the reconstruction tunnel being posterior to the lateral intercondylar ridge (resident’s ridge).
A large number of ACL reconstruction graft failures are in those patients who have the graft placed too posterior (central) on the tibia with an inability to control rotation of the knee or too anterior on the femur (anterior to resident’s ridge) or too central on the femur (effectively only reconstructing the anteromedial bundle), which leads to either stretching of the reconstruction graft or failure to control knee rotational laxity.