Comparison of kinematics of ACL-deficient and healthy knees during passive flexion and isometric leg press ☆ Fateme Esfandiarpour a , Ali Shakourirad b , Saeed Talebian Moghaddam c , Gholamreza Olyaei c , Abouzar Eslami d , Farzam Farahmand e, f, ⁎ a Department of Physical Therapy, Ahvaz Jundishapour University of Medical Sciences, Ahvaz, Iran b Advanced Diagnostic and Interventional Radiology Research Center (ADIR), Tehran University of Medical Sciences, Tehran, Iran c Faculty of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran d Institute for Informatics, Technical University of Munich, Munich, Germany e School of Mechanical Engineering, Sharif University of Technology, Tehran, Iran f RCSTIM, Tehran University of Medical Sciences, Tehran, Iran abstract article info Article history: Received 10 October 2011 Received in revised form 26 August 2012 Accepted 6 September 2012 Available online xxxx Keywords: 3D kinematics ACL injury Knee laxity Anterior tibial translation Closed chain exercise Background: Studying the kinematics of the ACL deficient (ACLD) knees, during different physiological activities and muscle contraction patterns, can improve our understanding of the joint's altered biomechanics due to ACL deficiency as well as the efficacy and safety of the rehabilitations exercises. Methods: Twenty-five male volunteers, including 11 normal and 14 unilateral ACLD subjects, participated in this study. The kinematics of the injured knees of the ACLD subjects was compared with their intact knees and the healthy group during passive flexion and isometric leg press with the knees flexed from full exten- sion to 45° flexion, with 15° intervals. An accurate registration algorithm was used to obtain the three dimen- sional kinematical parameters, from magnetic resonance images. Results: The ACL deficiency mainly altered the tibial anterior translation, and to some extent its internal rotation, with the change in other parameters not significant. During leg press, the anterior translation of the ACLD knees was significantly larger than that of the normal knees at 30° flexion, but not at 45°. Compar- ison of the anterior translations of the ACLD knees during leg press with that of the passive flexion revealed improved consistency (CVs changed from 1.2 and 4.0 to 0.6 and 0.6, at 30° and 45° flexion, respectively), but considerable larger translations (means increased by 6.2 and 4.9 mm, at 30° and 45° flexion, respectively). Conclusion: The simultaneous contraction of the quadriceps and hamstrings during leg press, although re- duces the knee laxity, cannot compensate for the loss of the ACL to restore the normal kinematics of the joint, at least during early flexion. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Anterior cruciate ligament (ACL) injury is one of the most prevalent and debilitating problems faced by knee patients and clinicians [1]. The stabilizing functions of the ACL, to limit the anterior tibial translation and to control the tibial axial rotation [2,3], are believed to be critical for maintaining the normal knee kinematics. Aberrant joint loading, due to the altered kinematics of the ACL deficient (ACLD) knees, has been considered responsible, at least in part, for the degenerative changes in the articular cartilage and the progressive development of knee osteoarthritis [4,5]. A thorough understanding of the effects of the ACL deficiency on the knee kinematics is essential to evaluate the efficacy of the surgical and rehabilitation treatment procedures and to prevent secondary dev- astating complications. In vitro cadaveric studies [6,7] have provided some insight into the kinematical behavior of the ACLD knees under controlled conditions. However, they are unable to accurately simulate the effects of weight bearing and muscles contraction on the joint kine- matics. The in-vivo kinematics of the joint might be assessed using medical imaging modalities, e.g., magnetic resonance imaging (MRI), which provide direct visualization of the position and hence the relative motion of the bones, noninvasively. The previous MRI studies of the knee kinematics, however, have often addressed only two or three of the joint kinematical parameters [8–10] and/or analyzed its contact pattern [8]. To the best of our knowledge, the only study describing The Knee xxx (2012) xxx–xxx ☆ Level of evidence: Controlled laboratory study using a repeated measure design, Level IIa. ⁎ Corresponding author at: School of Mechanical Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran. Tel.: +98 21 66165532; fax: +98 21 66000021. E-mail address: farahmand@sharif.edu (F. Farahmand). THEKNE-01640; No of Pages 6 0968-0160/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.knee.2012.09.009 Contents lists available at SciVerse ScienceDirect The Knee Please cite this article as: Esfandiarpour F, et al, Comparison of kinematics of ACL-deficient and healthy knees during passive flexion and isometric leg press, The Knee (2012), http://dx.doi.org/10.1016/j.knee.2012.09.009