Intraoperative photo of a femoral tunnel created through a transtibial tunnel during ACL reconstruction.
Courtesy of Bernard R. Bach, Jr., MD


Published 12/1/2009
Jennie McKee

Where do you stand in the AM vs. TT debate?

Is anteromedial or transtibial portal reaming more effective in ACL reconstruction—or is an open technique better?

Controversies abound in anterior cruciate ligament (ACL) reconstruction. Opinions differ on issues such as the most effective type of autograft or allograft to use, whether the single-bundle or double-bundle technique is better, and the optimal timing for surgery.

Yet another controversy involves the approach to preparing the femoral socket during arthroscopically assisted ACL reconstruction. Is the anteromedial (AM) portal or the transtibial (TT) technique more effective? Or should an open technique be used instead of an arthroscopic technique? AAOS Now spoke with Asheesh Bedi, MD; Bernard R. Bach Jr., MD; and K. Donald Shelbourne, MD, to find out which approach each favors and why.

Using the AM portal
Dr. Bedi noted that preparing the femoral tunnel through an AM portal “appears to provide a reliable means of restoring the footprint and obliquity of the native ligament.”

He bases this assertion in part on the results of recent studies, including one that he and his colleagues performed with 10 cadaveric knees randomized for ACL reconstruction using either a TT or an AM portal.

“In our study, the biomechanical outcomes after ACL reconstruction using an AM portal technique were superior to those achieved through the use of the TT portal,” said Dr. Bedi. “The AM portal technique was better able to restore the native ligament anatomy.

“Our study suggests that the improved ability to restore the footprints and obliquity of the ligament with the AM technique correlates with greater stability of the knee after ACL reconstruction,” added Dr. Bedi.

He also noted that recent work by both Freddie H. Fu, MD, and Mark E. Steiner, MD, and their research groups has confirmed that the conventional TT drilling technique results in a more vertical graft configuration and less biomechanical stability when directly compared to the AM portal technique.

The AM portal technique is safe and effective, he stated, but it has a learning curve.

“Without attention to detail, the surgeon risks creating a short femoral socket and injuring the medial femoral condyle,” said Dr. Bedi. “These pitfalls can be avoided, however, with an understanding of the technique and anatomy.”

Dr. Bedi and his mentor, David W. Altchek, MD, have described a ‘footprint technique’ for ACL reconstruction using the AM portal technique that helps to reliably avoid these issues.

Dr. Altchek recommends using flexible reamers during the AM technique.

“When you use flexible reamers, you basically don’t have to flex the knee at all while you’re reaming, so you can see well and can get to the right spot,” he said.

Dr. Bedi and his fellow researchers “certainly do not condemn the TT technique.”

“The TT technique has been used for years with good clinical outcomes,” he said, “and many excellent clinicians continue to advocate for its ability to restore knee stability and ACL anatomy.

“But in our experience,” he explained, “we have found that an anatomic femoral socket cannot be prepared with a TT technique without relatively posterior placement of the tibial tunnel or eccentric reaming and iatrogenic expansion of the tibial tunnel to achieve the desired position on the femur.”

Support for the TT technique
Dr. Bach has been using the TT technique since 1991. He agrees with Dr. Bedi that if a surgeon using the TT technique places the femoral tunnel too high in the intercondylar notch—meaning that the orientation of the tibial tunnel is not oblique enough—patients may have a normal Lachman test following surgery, but could go on to experience instability events.

To avoid this problem, Dr. Bach creates an accessory inferior portal through the patellar tendon.

“Creating an accessory portal allows me to rotate my tibial aiming device and create a very oblique orientation of the tibial tunnel,” said Dr. Bach. “I can then place my femoral offset aimer and rotate it down along the wall in a position that allows me to fill portions of the posterolateral (PL) and anteromedial (AM) bundles. Our anatomic studies demonstrate that we have about a 50-50 fill of the PL and AM bundles.

“If the surgeon doesn’t get some degree of fill of the PL bundle,” he added, “there will probably be a greater likelihood of failures involving the pivot shift phenomenon.”

In general, Dr. Bach uses a 55 degree angle on his variable angle tibial aimer, and uses the posterior edge of the anterior horn lateral meniscus in the coronal plane for intra-articular tibial pin placement.

Intraoperative photo of a femoral tunnel created through a transtibial tunnel during ACL reconstruction.
Courtesy of Bernard R. Bach, Jr., MD
This intraoperative photo shows the placement of the tibial and femoral tunnels during the mini-arthrotomy technique. The measurement tool is placed through both tunnels to confirm straight-line placement of the tunnels.
Courtesy of K. Donald Shelbourne, MD

Another error that can occur with the TT technique is a posteriorly placed tibial tunnel. Dr. Bach advised how to avoid the latter problem.

“After provisionally placing the TT femoral aimer and drilling a femoral pin, one can drill retrograde through the tibial tunnel into the joint, which will ream a small portion of the intra-articular tibial tunnel lip posteriorly,” he said. “One can then remove the pin and reamer and reposition the femoral aimer in a lower position along the wall.”

Dr. Bach went on to note that of the 2,400 primary ACL reconstructions that he and his fellow orthopaedic surgeons at Rush University have performed since 2000, they have revised a total of 43 of their own patients.

“These data show that we have a 1.5 percent failure rate for our total group, so what we’re doing seems to work well,” he said. Dr. Bach acknowledged, however, that the failure rate might be higher because some patients may have gone to see other physicians, decided not to have revisions, or not even known that they have a failed ACL graft.

Although he primarily uses the TT technique, Dr. Bach stated that the AM portal technique does have benefits.

“I can understand why people advocate that technique,” he said. “The advantage with establishing an accessory AM portal to create the femoral tunnel is that you have independent tunnels, so you’re not reliant upon the tibial tunnel to access the placement of your femoral tunnel.”

“I’ve used the AM technique on rare occasions,” continued Dr. Bach, “such as in revision surgeries where the femoral tunnel is more vertical than I want it to be, which means there may be some overlap in the tunnels. In that case, I can get a more oblique orientation with an AM portal. I might also consider using a two-incision technique and drill from outside-in on the femur.”

Dr. Bach also stated that “the disadvantage with creating an accessory AM portal and drilling through that portal is that you definitely have to hyperflex the knee more. It probably allows you to get a little more fill of the PL bundle, but there may be a higher like-lihood of creating a posterior wall blowout.

“I think if you do a good single-bundle technique and you fill both portions of the PL and AM bundle using either the AM or the TT technique, either technique will compare favorably in terms of rotational control,” summed up Dr. Bach.

In favor of the open technique
According to Dr. Shelbourne, rather than drilling an AM or a TT portal to reach the femoral tunnel in arthroscopically assisted ACL reconstruction, performing a mini-arthrotomy is the way to go.

“Using this open technique is the easiest way to drill both tunnels in the right spot,” Dr. Shelbourne said.

He asserted that “no study has ever shown that arthroscopically assisted ACLs are better than open ACLs.

“Back when arthroscopically assisted ACL reconstruction was becoming popular,” he said, “I compared the results of one of my partner’s arthroscopically assisted surgeries versus my open results. In that study, we showed that doing the surgery arthroscopically provides no rehabilitation advantage.”

He notes that the open technique is a straightforward, reproducible procedure.“It’s the same technique that I’ve used for 28 years and that no one has improved upon,” he said.

Dr. Shelbourne asserts that arthroscopic procedures are better suited for repairing injuries that are difficult to see during an open technique, such as meniscus tears.

“In ACL reconstruction, if you make an incision in the front of the knee just medial to the patella, both the tibia and the femur are easy to see. As long as you know where to drill the hole, there’s no way you can put it in the wrong spot,” he stated.

Orthopaedic surgeons must remember to think beyond the details of the ACL reconstruction procedure, adds Dr. Shelbourne.

“As surgeons, we sometimes think our job is just to perform surgery,” he said. “But we must consider all aspects of getting patients to their final outcome, including being involved in things such as patients’ preoperative and postoperative rehabilitation. The surgical procedure is a very small part of the whole package.”

Drs. Bedi and Altchek report no conflicts. Dr. Bach made the following disclosures: Smith & Nephew; DJ Orthopaedics; Miomed; Athletico, Ossur, Arthrex, and Scheck & Siress. Dr. Shelbourne had the following disclosures: Aircast (DJ); Kneebourne Therapeutics.

Jennie McKee is a staff writer for AAOS Now. She can be reached at

Additional Link:
Transtibial Versus Anteromedial Portal Reaming in ACL Reconstruction: An Anatomical and Biomechanical Evaluation of Surgical Technique