Tunnel Placement in ACL Reconstruction
Dr. Timothy Reish discusses the accessory medial portal technique he uses when reconstructing a tear of the anterior cruciate ligament.
Timothy G. Reish, MD
The author has no disclosures relevant to this article.
Accessory medial (AM) portal techniques were developed to address the problem of vertical tunnels that were associated with the tibial tunnel technique in anterior cruciate ligament (ACL) reconstruction. The drive has been based on trying to recreate anatomic (ie, the graft is inserted centrally onto the native ACL footprint) as compared with isometric placement of grafts.
Proponents of the AM portal technique claim it more readily recreates anatomic graft placement at the center of the native ACL insertion site. Several studies have shown that non-anatomic placement is the most common technical error leading to recurrent instability following ACL reconstruction. For example, while vertically placed grafts may resist anterior/posterior forces, they are less able to overcome the internal rotation component of ACL insufficiency.
The main benefit of using an AM portal is the increased freedom affording in drilling the femoral tunnel, as it is drilled independently of the tibia. In addition, the surgeon can place the tibial tunnel as desired, irrespective of necessary tradeoffs to make a proper femoral tunnel. This avoids the inherent restraint provided by drilling though a tibial tunnel, including a more vertical vector with a starting point higher on the intercondylar notch. The fixation interference screw can also be inserted in the proper vector through this same portal.
Other benefits include freedom from drilling guides and improved visualization as water pressure is not lost when an open tibial portal is established. Obvious risks involved with the AM portal technique include a shorter tunnel compared with the transtibial technique due to its more horizontal positioning.
The AM portal is more distal and medial then standard medial portals. When drilling, hyperflexion is necessary to increase the femoral tunnel length, avoid posterior blowout, optimize placement on the native footprint, and protect the peroneal nerve. The surgeon must also avoid damaging the medial femoral condyle when reaming.
Debate over tunnel placement in ACL reconstruction has existed for years and will likely continue. The ideal technique is the one suited to surgeon experience and patient anatomy.
Timothy G. Reish, MD, is an orthopaedic surgeon with the Insall Scott Kelly Institute for Orthopaedics and Sports Medicine. He specializes in knee and shoulder reconstruction.