In order to restore stability to the knee, your doctor may recommend an ACL reconstruction to insert a new ligament in the place of the damaged ACL. A new technique, called a double-bundle ACL reconstruction, has been developed to better replicate the function of the normal ACL.
What is an ACL "bundle"?
The anterior cruciate ligament is made of a tough, fibrous tissue that spans the knee joint, attaching to the femur (thigh bone) on top, and the tibia (shin bone) below. The ligament itself is made of thousands of individual fibers, that together form the ACL. Some of these fibers are organized into distinct bundles. The normal ACL has two primary bundles of fibers.
These bundles are positioned closely together, in some patients with normal ACLs it can be difficult to discern distinct bundles. But we know there are two primary bundles, and each bundle is named for its location. The longer anteromedial bundle is positioned in front of the shorter posterolateral bundle.
How is a single-bundle ACL reconstruction performed?
Most ACL reconstruction surgeries are done using a single-bundle reconstruction. A single-bundle ACL reconstruction uses a tendon graft to replace the torn ACL. Unfortunately, ACL tears cannot be repaired, or sewn together, and a graft must be used to reconstruct the ligament. When the ACL is reconstructed, the graft is placed in the position of the anteromedial bundle.
Grafts are held in place by making a hole in the bone called a tunnel. One tunnel is made in the femur and one in the tibia. The graft is held in the bone with a fixation device, often a screw.
How does a double-bundle ACL reconstruction work?
Instead of placing just one larger graft, the double-bundle ACL reconstruction procedure uses two smaller grafts. Therefore, there are essentially two ligament reconstructions, one for each bundle. The double-bundle procedure requires two additional bone tunnels to accommodate a second graft, and one additional incision.
Does the double-bundle ACL work better?
Studies have demonstrated some advantages of the double-bundle ACL reconstruction. These studies show more 'normal' function of the reconstructed ligament after this double-bundle ACL reconstruction surgery. What is not known is if this means the patients will have better success with the double-bundle ACL reconstructions.
Are there disadvantages to the double-bundle ACL reconstruction?
This is a new procedure, and as is the case with any new procedure, the long-term results are not well understood. It is possible that this procedure will be an improvement on the standard single-bundle ACL reconstructions, but it is also possible that these patients may have the same, or even worse, long-term results. No one really knows just yet.
The double-bundle is technically more demanding of a procedure, and there are fewer surgeons with experience in this surgical technique.
Should I ask to have a double-bundle ACL reconstruction?
It is not clear that the double-bundle ACL reconstruction is a better procedure, but some patients are willing to try a new procedure in an effort to possibly improve their long-term result. Standard single-bundle ACL reconstructions have excellent results, with about 90% of patients able to return to activities at their pre-injury level. However, the results are not 100%, and some patients have persistent instability after ACL reconstructions, and may develop problems later in life.
The double-bundle ACL reconstruction is an effort to improve the results of an already excellent procedure. If you are interested, talk to your doctor about this procedure. As mentioned, few surgeons perform the double-bundle ACL reconstruction. But you can certainly discuss this procedure with your doctor and get his or her thoughts on the double-bundle ACL reconstruction.
Zantop T, et al. "The role of the anteromedial and posterolateral bundles of the anterior cruciate ligament in anterior tibial translation and internal rotation" Am J Sports Med 2007;35:223-7.
Chabbra A, et al. "Anatomic, Radiographic, Biomechanical, and Kinematic Evaluation of the Anterior Cruciate Ligament and Its Two Functional Bundles" J Bone Joint Surg Am 2006;88(Supp 4):2-10.
Fu F, et al. "Anatomic Double-Bundle ACL Reconstruction: Patient Information Handout/Frequently Asked Questions" Univ of Pitt, Dept of Orthop Surg; Feb 2007.