Key term: Kinematics
The Anterior Cruciate Ligament (ACL) is the main support structure of the knee. It prevents excessive translation and rotation of the femur (thigh bone) on the tibia (shin bone). When you tear your ACL, your knee may buckle or “give out” with change of direction and pivoting activities. In order to regain stability in the knee, an ACL reconstruction must be done.
More than 100,000 anterior cruciate ligament reconstructions are performed every year in the United States. Good to excellent outcomes for ACL reconstruction performed with current surgical techniques (Single-Bundle) range from 70% to 95%. Degenerative changes occur in 90% of patients 7 years after single-bundle ACL reconstruction and only approximately 50% of patients return to their previous level of activity.
When orthopedic surgeons began doing ACL reconstructions, it was a technically demanding procedure, however, over time, development of new techniques enabled us to improve both our outcomes and our understanding of this complex structure.
The ACL is comprised of two separate functional bundles of fascicles, not a single cord. Traditional ACL reconstruction treats the ligament as though it were a single construct, replicating one of the functional bundles but not the other. [at left: Right knee joint. Soft tissues have been removed to inspect the ACL. Note two distinct bundles, the anteromedial and posterolateral bundles.[
As our understanding of the basic science and anatomy of the ACL has increased, and the technology has improved, orthopedic surgeons now have the opportunity to more closely replicate the natural anatomy of the ACL. Doing it as we have in the past is effective, but there is room for improvement, particularly in restoring normal kinematics. The anatomic double-bundle technique may offer us that opportunity.
In the long run, a double-bundle technique, by more closely replicating the normal anatomy of the ACL, could improve knee kinematics, resulting in more normal functioning and reducing the incidence of degenerative arthritis.
If you hang a door by only one hinge, the door will hang crooked and the bottom may stick out and wear unevenly. If you add a second hinge, you make the door more level and eliminate that erosion. With single bundle repair, you have one hinge, with the anatomic doublebundle approach, you add the second hinge.
Short term results seem to bear out the theory. Patients who have double-bundle ACL repair regain range of motion more quickly with better overall stability than those who have traditional single-bundle ACL reconstruction.
Although other studies have shown no statistical difference between single-bundle and double-bundle ACL reconstruction using various measures, better three dimensional tests have to be developed to more objectively evaluate the difference between these two techniques.
In summary with traditional single-bundle ACL reconstruction, a single graft is used to basically replicate the positioning of the Anteromedial (AM) bundle. The double-bundle technique uses two separate grafts to replicate the positioning of both the Anteromedial (AM) and Posterolateral (PL) bundles. Because the AM bundle makes a greater contribution to translational knee stability and the PL bundle makes a greater contribution to rotational stability, a double-bundle technique may be better able to restore normal knee kinematics, and minimize risk of degenerative arthritis.