Reviewed by – Dr. Satish Reddy
Disruption of the ACL (anterior cruciate ligament) is among the most frequent musculoskeletal injuries affecting physically active men and women. It is one of the most common sports injuries. ACL reconstruction surgery is a widely accepted approach for treating tears, but continues to evolve, with many technical issues that are under debate among the orthopedic surgeons. They mainly include the graft selection and surgical technique i.e. double versus single bundle.
Anatomy of ACL
Anatomical and biomechanical observational studies have shown that The anterior cruciate ligament mainly consists of 2 distinct bundles:
- Anteromedial (AM) bundle
- Posterolateral (PL) bundle
When the knee is in extension (straight) position, the AM and PL bundles are parallel. When the knee is flexed, the 2 bundles cross each other. Most patients who tear their anterior cruciate ligament damage both bundles at the same time.
Each bundle acts differently to stabilize the knee. The anteromedial (AM) bundle AM bundle provides more stability in the anterior-posterior direction and is isometric, meaning it functions equally throughout the full movement of the knee.
The posterolateral (PL) bundle PL bundle provides anterior-posterior (front and back) stability when the knee is in a straight position and rotational stability during pivoting and twisting movements.
What is a Single Bundle v/s a Double Bundle ACL Surgery?
Single Bundle ACL Reconstruction
Most ACL reconstructions are done using a single-bundle reconstruction technique. In single-bundle ACL reconstruction surgery, a tendon graft is used to replace the torn anterior cruciate ligament. Unfortunately, ACL tears cannot be sewn or repaired together, and graft (ex; autograft or allograft) must be used to reconstruct the torn ligaments.
When the anterior cruciate ligament is reconstructed, the graft is placed in the position of the anteromedial bundle (AM).
Grafts are held in place by making small holes in the bones called a tunnel. One tunnel is made in the femur(thigh bone) and one in the tibia (shin bone). After placing the graft, its ends are fixed with screws.
Double Bundle ACL Reconstruction
In double-bundle anterior cruciate ligament reconstruction procedure, 2 smaller grafts are used Instead of placing just one larger graft.
Therefore, there are essentially 2 ligament reconstructions, one for each bundle. The double-bundle procedure requires 2 additional bone tunnels to accommodate a second graft and one additional incision.
Traditionally, only one bundle of the anterior cruciate ligament has been reconstructed (commonly the anteromedial bundle) with good reported short-term results. However, with longer follow-up and more critical evaluation, traditional single bundle ACL’s don’t seem to do as well as we once thought. Many patients (as many as 1/3rd) suffer from recurrent knee instability and early onset arthritis (up to 90 percent 10 years after surgery).
Thus, the double bundle technique of ACL was developed. This procedure reconstructs both the AM and PL bundles of the anterior cruciate ligament.
Single Bundle or a Double-Bundle Reconstruction which is better?
Short-term results (in humans and cadavers) from several research studies (NCBI) suggest that the Double-Bundle Reconstruction appears to have some promising results for the right indications and done with proper technique. There is still debate and no real conclusion on whether either technique is conclusively better.
The refining technique with single bundle reconstruction may improve results as well without the increased risk of a more technically challenging procedure.
The hope with the new double-bundle ACL surgery procedure is that more patients will have stable knees, will be able to participate better in sports and regular activities, and will have a reduced incidence of future osteoarthritis of the knee.
This only makes sense, because the double bundle procedure is more likely to restore the normal anterior cruciate ligament anatomy and biomechanics versus the single bundle technique.
Why consider double bundle?
- Single-Bundle Anterior cruciate ligament reconstruction does not adequately restore normal knee stability, particularly tibial rotation.
- Double-Bundle Reconstruction better restores knee stability.
Why not choose double bundle?
- The technique is more demanding and not every surgeon may be expert in it.
- In case the ACL reconstruction fails, the presence of two tunnels creates more complexity for a revision surgery
While the debate between which technique better continues, as a patient, awareness of these techniques can help you have an informed discussion with your doctor. It is also important to find out which technique the doctor specializes in which technique, and take independent second opinions from a few doctors about which option would be best given your personal goals and medical condition.
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