Can the ACL heal by itself?
Some knee ligaments, such as the medial collateral ligament (MCL), heal reliably without surgery. Some partially torn ACLs, particularly in children and adolescents, may also heal without surgery. However, a complete tear of the ACL rarely heals. This is probably due to the amount of energy involved in the injury, the lack of blood supply, and the interior location of the ACL. The torn ACL may scar back to the intact PCL within the knee, but this rarely returns stability to the knee. In fact, even when the ends of a torn ligament are sutured together (called a primary or direct repair), the ligament does not reliably heal. Therefore, surgery for a complete ACL tear (an ACL reconstruction) involves replacing the ACL with other tissue (a graft).

Is surgery always needed for an ACL tear?
Surgery is not required for all ACL injuries. Partial tears, in which a physical examination shows a relatively stable knee, may be treated with bracing and rehabilitation. Even some patients with complete ACL tears do not need reconstruction. These "copers" are typically older patients with lower physical activity, who do not participate in pivoting and cutting activities.

Why should the ACL be reconstructed?
One reason to reconstruct the ACL is to provide knee stability that allows for return to activities and sports. Another reason is to provide knee stability in order to prevent more injury, such as a meniscal tear, which may eventually lead to degenerative joint disease.

Is an MRI needed to diagnose an ACL tear?
An MRI is not always required to diagnose an ACL tear. An ACL tear can be accurately diagnosed with a physical examination. However, when the knee is very swollen and painful, an accurate examination can be difficult. Also, an MRI can be useful to reveal other associated injuries such as meniscal tears, a PCL tear, or injury to other supporting structures.

Which is the best graft to use for an ACL reconstruction?
There are advantages and disadvantages to the many technical aspects of an ACL reconstruction including the type of graft, methods of securing the graft, and rehabilitation protocols. There is no clear consensus as to which graft is best. In the end, the surgeon's experience with the chosen technique and the patient's commitment to the rehabilitation program are probably more important factors in a functional outcome.

When can I play sports again after ACL reconstruction?
Rehabilitation programs after ACL reconstruction are constantly evolving, shortening the return to sports. Most patients can start to return to their sports about 6 months after reconstruction.

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