Double-Bundle ACL Reconstruction
Anatomy is the foundation of orthopaedic surgery. The advancing knowledge of the anterior cruciate ligament (ACL) has led to the development of modern, improved reconstruction techniques that help restore the anatomy of the native ACL, which consists of two functional bundles: the anteromedial (AM) and posterolateral (PL) bundles. (Figure 1)
Figure 1. Lateral portal view of the two-bundle anatomy of the ACL of a left knee. The anteromedial (AM) and posterolateral (PL) bundle are indicated by the arrows.
Recently there has been much discussion as to whether the ACL should be reconstructed as a single or a double bundle. However, the question should not be about single- or double-bundle reconstruction, but rather about how to restore the anatomy to the fullest extent. Anatomic ACL reconstruction is defined as the functional restoration of the ACL to its native dimensions, collagen orientation, and insertion sites. The four principles of anatomic ACL reconstruction are to:
- Restore the two functional bundles (whether with a single- or double-bundle)
- Restore the insertion sites
- Replicate the native tensioning pattern
- Individualize the surgery for each patient
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Non-Anatomic ACL Reconstruction Does Not Promote Long-Term Knee Health
It has been shown that traditional, non-anatomic, single-bundle ACL reconstruction does not prevent the occurrence of early osteoarthritis. This traditional ACL reconstruction technique places the ACL graft outside of the native insertion site 3,4 and therefore fails to restore the normal knee kinematics. It has been hypothesized that these abnormal knee kinematics contribute to the development of osteoarthritis after ACL reconstruction. Before we discuss whether to perform single- or double-bundle reconstruction, we first need to place the ACL in the anatomic position. Anatomic placement of the graft helps to restore normal knee anatomy and function and therefore helps to promote long-term knee health.
How Much of the ACL Do We Need to Restore?
The ACL comes in a variety of shapes and sizes (Figure 2). The native ACL insertion site size ranges from 12 mm to 22 mm. A single tunnel of 10 mm diameter would cover 80-90% of the native ACL insertion site if the native ACL insertion site were only 12 mm. However, if the native ACL were 22 mm, a single tunnel of 10 mm diameter may cover less than half of the native ACL insertion site. Double-bundle reconstruction would result in better coverage of the native insertion site in these cases. This illustrates that ACL reconstruction should be performed in an anatomic fashion and individualized to tailor the ACL to each patient’s specific needs.
Figure 2. Lateral portal view of the tibial ACL insertion site. Tibial insertion site of 14 mm, left, and tibial insertion site of 22 mm, right. These examples show the large variation in ACL insertion site size.
The Two Bundles Work Together
The two functional bundles of the native ACL work synergistically. Together, they provide stability while allowing normal knee range of motion. Anatomic single-bundle ACL reconstruction restores the ACL as one bundle; double-bundle ACL reconstruction restores the ACL as two bundles, allowing each bundle to be tensioned separately to better replicate the native ACL tension pattern.
Outcome Evaluation
To determine if there is a difference in outcome between single- and double-bundle ACL reconstructions, we need high-quality, randomized clinical studies. However, we also need to focus on improving our outcome measures. Physical examination and patient reported outcome scores may not be enough to demonstrate the subtle, yet important differences between the techniques. More accurate, reliable, and precise outcomes measures – including biology, imaging and kinematic testing – are needed.
The paradigm in ACL surgery is changing. New reconstruction techniques are being developed, and there is a need to compare these various techniques. There is no definitive answer as to whether single- or double-bundle reconstruction is better at this time. The best answer is that it probably depends on the patient’s individual characteristics with regards to ACL size, activity level, co-morbidities, and more.
Regardless of the choice for single or double bundle, ACL reconstruction should be performed in an anatomic fashion. By restoring normal knee anatomy and kinematics, we can potentially eliminate risk factors and help to prevent the development of osteoarthritis. Osteoarthritis has a major impact on quality of life and its prevention is part of our vow to provide the best possible care for our patients.
Reprinted with permission from the Fall 2010 issue of COA Bulletin
References
- van Eck CF, Lesniak BP, Schreiber VM, Fu FH Anatomic Single- and Double-Bundle Anterior Cruciate Ligament Reconstruction Flowchart. Arthroscopy 2010;26-2:258-68.
- Lohmander LS, Ostenberg A, Englund M, Roos H. High prevalence of knee osteoarthritis, pain, and functional limitations in female soccer players twelve years after anterior cruciate ligament injury. Arthritis Rheum 2004;50-10:3145-52.
- Forsythe B, Kopf S, Wong AK, Martins CA, Anderst W, Tashman S, Fu FH. The location of femoral and tibial tunnels in anatomic double-bundle anterior cruciate ligament reconstruction analyzed by three-dimensional computed tomography models. J Bone Joint Surg Am 2010;92-6:1418-26.
- Kopf S, Pombo MW, Szczodry M, Irrgang J, Fu FH. Size variability of the human anterior cruciate ligament insertion sites. Am J Sports Med 2011;39(1):108-13.
- Tashman S, Collon D, Anderson K, Kolowich P, Anderst W. Abnormal rotational knee motion during running after anterior cruciate ligament reconstruction. Am J Sports Med 2004;32-4:975-83.
