Measurement of the End-to-End Distances Between the Fe and Tibial Insertion Sites of the Anterior Cruciate Ligame During Knee Flexion and With Rotational Torque Joon Ho Wang, M.D.,Ph.D.,Yuki Kato, M.D.,Ph.D.,Sheila J. M. Ingham, M.D.,M.S., Akira Maeyama, M.D.,Ph.D.,Monica Linde-Rosen, B.S.,R.N., Patrick Smolinski, Ph.D.,and Freddie H. Fu,M.D.,D.Sc., D.Ps.(Hon.) Purpose: The aim of this study was to determine the end-to-end distance changes in anterior cruciate ligament (ACL) fibers during flexion/extension and internal/external rotation of the knee. Methods: The positional relation between the femur and tibia of 10 knees was digitized on a robotic system during flexion/extension and with an internal/external rotational torque (5 Nm). The ACL insertion site data, acquired by 3-dimensional scanning, were superimposed on the positional data.The end-to-end distances of 5 representative points on the femoral and tibial insertion sites of the ACL were calculated. Results: The end-to-end distances of all representative points except the most anterior points were longest at full extension and shortest at 90°. The distances of the anteromedial (AM) and posterolateral (PL) bundles were 37.2 ⫾ 2.1 mm and 27.5 ⫾ 2.8 mm, respectively, at full extension and 34.7 ⫾ 2.4 mm and 20.7 ⫾ 2.3 mm, respectively, at 90°. Only 4 knees had an isometric point,which was 1 of the 3 anterior points. Under an internal torque, both bundles became longer with statistical meaning at all flexion angles (P ⫾ .005). The end-to-end distances of all points became longest with internal torque at full extension and shortest with an external torque at 90°. Conclusions: Only 4 of 10 specimens had an isometric point at a variable anterior point.The end-to-end distances of the AM and PL bundles were longer in extension and shorter in flexion. Clinical Relevance: The nonisometric tendency of the ACL and the end-to-end distance change during knee flexion/extension and internal/external rotation should be considered during ACL reconstruction to avoid overconstraint of the graft. A lthough an excellent understanding of anatomy is fundamental to orthopaedic surgeries, 1 anatomic anterior cruciate ligament (ACL) reconstruction 2 can be a great challenge because of the complexity of the un- derlying anatomic structures. 3 Numerous anatomic stud- ies have shown that the ACL consists of 2 functional bundles, the anteromedial bundle (AMB) and posterol eralbundle (PLB), 4-6 which have distinct functions. 4,7 Anatomic double-bundle reconstruction techniques th attempt to re-create both ACL bundles have been deve From the Department of Orthopaedic Surgery, School of Medicine (J.H.W., Y.K., S.J.M.I., A.M., M.L-R., P.S., F.H.F.), and D of Mechanical Engineering and Material Science (P.S., F.H.F.), University of Pittsburgh, Pittsburgh, Pennsylvania, U.S.A.; D Orthopaedic Surgery, School of Medicine, Sungkyunkwan University, Samsung Medical Center (J.H.W.), Seoul, South Korea of Orthopaedic Surgery, School of Medicine, Nihon University (Y.K.), Tokyo, Japan; and Department of Orthopaedic Surgery, School of Medicine, Fukuoka University (A.M.), Fukuoka, Japan. The authors report the following potential conflict of interest or source of funding in relation to this article: Korea Researc Grant (KRF-2008-013-E00034) and the Albert B. Ferguson, Jr., M.D.,Orthopaedic Fund of The Pittsburgh Foundation. Received March 28, 2011; accepted March 9, 2012. Address correspondence to Freddie H. Fu, M.D., D.Sc., D.Ps.(Hon.), Department of Orthopaedic Surgery, School of Medic of Pittsburgh, 3471 Fifth Ave, Ste 1011, Pittsburgh, PA 15213-3221, U.S.A.E-mail: ffu@upmc.edu © 2012 by the Arthroscopy Association of North America 0749-8063/11201/$36.00 doi:10.1016/j.arthro.2012.03.004 1524 Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 28,No 10 (October), 2012: pp 1524-1532