Advanced MR Imaging of the Cruciate Ligaments Catherine C. Roberts, MD a,*, Jeffrey D. Towers, MD b, Mark J. Spangehl, MD c, John A. Carrino, MD, MPH d, William B. Morrison, MD e The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are essential to knee stability and movement. These ligaments are named by the location of their tibial attachments. Each ligament is composed of separate functional bundles that differ in size but are equally important in function. MR imaging best delineates these struc- tures in the acutely injured, chronically injured, and reconstructed states. Normal anatomy and sectional appearance Anterior cruciate ligament The ACL extends from the posteromedial aspect of the lateral femoral condyle to the anteromedial tib- ial plateau, just anterior to the intercondylar emi- nence [1]. The femoral attachment is not at the intercondylar notch [1,2], which is a common mis- conception. On axial images it can be seen reliably R A D I O L O G I C C L I N I C S O F N O R T H A M E R I C A Radiol Clin N Am 45 (2007) 1003���1016 This article was originally published in Magnetic Resonance Imaging Clinics of North America 15:1, February 2007. a Department of Radiology, Mayo Clinic College of Medicine, 13400 East Shea Boulevard, Scottsdale, AZ 85259, USA b Division of Musculoskeletal Imaging, Department of Radiology, University of Pittsburgh Medical Center, 200 Lothrop Street, Pittsburgh, PA 15213, USA c Department of Orthopedic Surgery, Mayo Clinic College of Medicine, 13400 East Shea Boulevard, Scottsdale, AZ 85259, USA d Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, 601 North Caroline Street, JHOC 5165, Baltimore, MD 21287, USA e Thomas Jefferson University Hospital, 132 South 10th Street, Suite 1079a, Philadelphia, PA 19107, USA * Corresponding author. E-mail address: roberts.catherine@mayo.edu (C.C. Roberts). - Normal anatomy and sectional appearance Anterior cruciate ligament Posterior cruciate ligament - Anterior cruciate ligament acute injury Typical tears Associated injuries and findings Atypical tears and pitfalls Anterior cruciate ligament chronic injury - Posterior cruciate ligament acute injury Typical tears and associated injuries Atypical tears and pitfalls - Posterior cruciate ligament chronic injury - Anterior cruciate ligament reconstruction Single-bundle/double-bundle technique Evaluation of fixation and graft Complications Associated findings and mimics of graft failure - Posterior cruciate ligament reconstruction Appearance and failure Complications - Summary - References 1003 0033-8389/07/$ ��� see front matter �� 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.rcl.2007.08.007 radiologic.theclinics.com

on the first image in which the femoral articular car- tilage is seen (Fig. 1). The ligament is intra-articular but extra-synovial [2]. The ACL is significantly small- er in women, with respect to measurements of vol- ume, mass, area, and length [3,4]. The apparent difference between men and women, with regard to ACL size and body weight, and intercondylar notch size, is a controversial topic [3,5]. The ACL can be divided into anteromedial bun- dles (AMB) and posterolateral bundles (PLB) based on function, although there is no histologic separa- tion [2,6]. The bundles are named by their relative attachment sites on the tibia. The AMB restrains an- terior tibial translation relative to the femur, whereas the PLB restrains rotation in near full ex- tension [7]. The AMB rotates laterally around the PLB during knee flexion [2]. Distal fibers of the ACL may extend to the anterior and posterior horns of the lateral meniscus [1,2]. An anatomic variant, consisting of a deltoid-shaped tibial attachment ex- tending the length of the transverse meniscal liga- ment in the coronal plane, can predispose to impingement and synovitis [8]. On MR imaging, the ACL is seen as an obliquely oriented band of low T1- and T2-weighted signal ly- ing within the lateral aspect of the intercondylar notch. On sagittal images with the knee extended, the ACL bundles are relatively parallel [2]. The PLB is taut, whereas the AMB is slack [1,7]. Imaging the knee with a mild degree of flexion, specifically 30 degrees in one study [9], has been shown to de- crease volume averaging in the region of the inter- condylar notch, and thus better delineate the ACL. The straight anterior border of the ACL should nearly parallel the Blumensaat line (roof of the in- tercondylar notch) [10,11]. Posterior cruciate ligament The PCL is larger and stronger than the ACL [12] and functions to restrain posterior tibial translation relative to the femur [12]. The femoral attachment is along the medial side and medial roof of the in- tercondylar notch. The tibial attachment is along the midline dorsal aspect of the tibial plateau, be- tween the meniscal roots. The PCL tibial attach- ment also extends over the dorsal rim of the posterior tibial shelf. The PCL can be divided into two functional bundles, the anterolateral bundle (ALB) and the posteromedial bundle (PMB) [12]. The bundles are named based on the location of their femoral attachments. The two bundles main- tain their anterior and posterior locations during motion of the knee and do not rotate around each other [12], as is seen with the bundles of the ACL. The ALB is larger and stronger, but has a co- dominant role with the PMB in stabilizing the knee [13]. Additional posterior oblique fibers of the PCL have been described and can be confused with the posterior meniscofemoral ligament [12]. The meniscofemoral ligaments extend from the posterior horn of the lateral meniscus to the medial femoral condyle. The meniscofemoral ligament ly- ing posterior to the PCL is also known as the liga- ment of Wrisberg. The meniscofemoral ligament lying anterior to the PCL is also known as the liga- ment of Humphrey and may mimic an intact PCL in the presence of a PCL tear. On MR imaging with the knee in an extended po- sition, the normal PCL is seen as a broad band of low T1- and T2-weighted signal, near the midline of the knee, extending from the femoral intercondy- lar notch to the posterior tibial plateau. On sagittal images with the knee extended, the PCL has a gently Fig. 1. Normal femoral attachment of the ACL on proton density MR imaging. (A) Axial section above common level of ACL origin and femoral articular cartilage. (B) Axial level of ACL attachment (arrow) and femoral artic- ular cartilage (arrowheads). Roberts et al 1004