When two are better than one

By: Annie Hayashi

By Annie Hayashi


According to Freddie Fu, MD, DSc (Hon), DPs (Hon), co-author of the award-winning scientific exhibit, “Application of anatomic double bundle reconstruction concept in revision/augmentation ACL surgeries,” double-bundle ACL reconstruction “is a concept rather than a technique.” Dr. Fu believes that this “concept” can also be applied to revisions and augmentations of single-bundle ACL reconstructions to restore the knee to its normal anatomy.

The concept of the double-bundle ACL is based on three primary principles—ligament anatomy, insertion site, and the tension pattern of the two bundles—individualized to the specific patient’s knee.

Dr. Fu believes this type of reconstruction gives the patient “the best possible advantage.” Taking the necessary time at the outset of the surgery is important to a long-term, favorable outcome. “I used to be able to do an ACL in 20 minutes,” says Dr. Fu. “Now it takes me 20 minutes to identify the appropriate insertion sites. This is a matter of providing the best possible patient care.”

Patient’s anatomy must be deciding factor
Although Dr. Fu is a strong proponent of the double-bundle ACL reconstruction procedure, he recognizes that single-bundle reconstruction may be appropriate for some patients. Approximately 20 percent of ACL reconstructions performed in Dr. Fu’s group practice are single-bundle ACL reconstructions. These patients have a smaller native insertion site (length less than 12 mm), open growth plates, multiple ligament injuries, and severe arthritic changes.

The ACL is comprised of two bundles: the anteromedial (AM) and the posterolateral (PL). Cadaveric studies have shown that the AM bundle is approximately twice as long as the PL bundle.

The two bundles of the ACL can be identified during fetal development, according to Dr. Fu, and they remain separate and distinct throughout life, although the size of each bundle will change over time.

Dr. Fu’s group has found that the AM and PL bundles tend to “merge” over time. By drilling three portals, they are able to view a larger area (Fig.1). “The more anatomy you are able to visualize, the better. It allows the surgeon to place the graft more accurately.”

Fig.1 Drilling three portals facilitates a larger viewing area. AMP, anteromedialportal; MP, medial portal; LP, lateral portal.

Executing the “principles”
The tibial and femoral insertion sites of the AM and PL bundles are marked for anatomic tunnel placement. Dr. Fu underscores the importance of connecting the tibial AM and femoral AM and the tibial PL to the femoral PL to reconstruct the ACL according to the patient’s individual anatomy.

Setting the tension pattern of the ACL is critical to the success of this procedure. “The AM bundle tightens in flexion as the PL handle becomes lax,” Dr. Fu explains. “The PL bundle tightens in extension as the AM bundle relaxes.”

The AM bundle reaches its highest level of tension at 45 degrees to 60 degrees of flexion; the PL bundle has its highest tension at 0 degrees to 15 degrees of flexion. Dr. Fu recommends adjusting the AM and PL grafts and fixing them at these angles of flexion to “closely reproduce the native tension pattern.”

Other uses for double-bundle reconstruction
Dr. Fu proposes using double-bundle reconstruction ACL surgery for AM or PL bundle augmentation surgery in partial ACL tears. “A careful dissection may reveal an isolated tear of either the AM or the PL bundle, where the other bundle may be preserved,” explains Dr. Fu. “Preserving the intact bundle by augmenting the injured bundle is a logical approach to ACL reconstruction.”

He has also used this procedure for revisions of ACL reconstructions. With those patients, he suggests “analyzing the position of the previous ACL graft, its specific tibial and femoral tunnel sites, and the relationship to anatomic insertion sites of the AM and PL bundles.”

In most of the single-bundle revisions he has encountered, the femoral tunnel is placed at a high AM position.

When double bundles fail
Most failures are due to patients returning to strenuous sports activity too quickly after surgery, according to Dr. Fu. They have not found that double-bundle reconstructions are failing as a result of “nonanatomic tunnel placement.” If revision is needed, the same anatomic reconstruction concept can be applied. For most patients, one single tibial tunnel can accommodate both the AM and PL grafts, although sometimes, Dr. Fu re-drills and dilates the two tunnels for reuse. He often uses the “over the top” position for femoral AM tunnel placement if insufficient space is available on the femoral notch for placement of the AM tunnel (Fig.2).

Fig.2 Double-bundle technique.

Working with the body
Since the ACL consists of two bundles that contribute to knee kinematics, Dr. Fu believes that the anatomy should be restored by “reproducing the two-bundle anatomy, the insertion sites, and the tension patterns.” For that restoration to be successful, it must be individualized to the patient’s anatomical requirements and needs. “We owe the best possible care to our patients,” Dr. Fu concludes.