The Relation Between Knee Flexion Angle and Anterior Cruciate Ligament Femoral Tunnel Characteristics: A Cadaveric Study Comparing a Standard and a Far Anteromedial Portal Damon Alavekios, M.D., Alexander Peterson, B.S., John Patton, B.S., Michelle H. McGarry, M.S., and Thay Q. Lee, Ph.D. Purpose: The purpose of this study was to compare the anterior cruciate ligament (ACL) femoral tunnel characteristics between 2 common arthroscopic portals used for ACL reconstruction, a standard anteromedial portal and a far ante- romedial portal. Methods: Seven cadaveric knees were used. A 1.25-mm Kirschner wire was drilled through the center of the ACL femoral footprint and through the distal femur from the standard anteromedial and far anteromedial portals at knee flexion angles of 100  , 120  , and 140  . No formal tunnels were drilled. Each tunnel exit point was marked with a colored pin. After all tunnels were created, the specimens were digitized with a MicroScribe device (Revware, Raleigh, NC) to measure the tunnel length; distance to the posterior femoral cortical wall (posterior cortical margin); and tunnel orientation in the sagittal, coronal, and axial planes. Results: The standard anteromedial portal resulted in a longer tunnel length, a less horizontal tunnel in the coronal plane, and a greater posterior cortical margin compared with the far anteromedial portal at all knee flexion angles. For both portal locations, the tunnel length and posterior cortical margin increased, and the tunnel position became more horizontal in the coronal plane, more anterior in the sagittal plane, and less horizontal in the transverse plane as knee flexion increased. Conclusions: Portal position affects femoral tunnel characteristics, with results favoring the more laterally positioned standard anteromedial portal at all flexion angles. Increasing the knee flexion angle leads to a longer femoral tunnel length and posterior femoral cortical margin with either portal position. Clinical Relevance: Understanding how portal positioning and knee flexion angle affect femoral tunnel orientation and characteristics may lead to improved surgical outcomes after ACL reconstruction. R ecently, there has been a push toward anatomic restoration of the anterior cruciate ligament (ACL) when performing reconstructions. Studies show that when reconstructing the ACL, anatomic placement leads to more native knee kinematics. 1-5 Traditional methods of ACL reconstruction, such as the transtibial technique, lead to nonanatomic femoral tunnel place- ment. 6-8 More recent technical changes to address this concern include independent drilling of the femoral tunnel through an anteromedial portal or far accessory anteromedial portal. 6-8 The independent drilling technique does have some drawbacks, however, including the possibility of dam- age to the medial femoral condyle articular cartilage, potential for damage to the common peroneal nerve and lateral collateral ligament, a shorter femoral tunnel, and the possibility of posterior cortex breach when drilling the femoral tunnel. 9,10 When creating the femoral tunnel through the standard anteromedial portal, surgeons often place the knee at a high angle of knee flexion of 120  or greater to prevent posterior cortical wall blowout and short femoral tunnels, as well as to avoid soft tissues at the femoral tunnel outlet. 11-13 Many surgeons choose to drill the femoral tunnel using From the Orthopaedic Biomechanics Laboratory, VA Long Beach Health- care System (D.A., A.P., J.P., M.H.M., T.Q.L.), Long Beach, California; and Department of Orthopaedic Surgery, University of California, Irvine (D.A., T.Q.L.), Irvine, California, U.S.A. The authors report the following potential conflict of interest or source of funding: D.A., A.P., J.P., and M.H.M. receive support from VA Rehabilitation Research and Development Merit Review. T.Q.L. receives support from VA Rehabilitation Research and Development Merit Review, ConMed, DePuy, Corentec, Eleven Blade, Arthrex, Arthrocare, Accumed, Stryker, Tornier, U&I, B. Braun, Cellcotec. Received August 21, 2013; accepted May 21, 2014. Address correspondence to Thay Q. Lee, Ph.D., Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System (09/151), 5901 E 7th St, Long Beach, CA 90822, U.S.A. E-mail: tqlee@med.va.gov Published by Elsevier Inc. on behalf of the Arthroscopy Association of North America 0749-8063/13610/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.05.031 1468 Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 30, No 11 (November), 2014: pp 1468-1474