MR Imaging of ACL Injuries in Pediatric and Adolescent Patients Victor M. Ho-Fung, MD*, Camilo Jaimes, MD, Diego Jaramillo, MD, MPH KEYWORDS • Anterior cruciate ligament • Pediatric imaging • Musculoskeletal • MRI • Trauma • Sports injuries Magnetic resonance (MR) imaging of older children and adolescents who have suffered knee trauma has greatly improved the diagnostic evaluation of anterior cruciate ligament (ACL) tears and related injuries. Normal morphology, signal char- acteristics, and course of the ACL on MR images are well described in adults. 1,2 However, interpretation of diagnostic images in children requires a comprehensive understanding of normal development-related changes and injuries that are unique to the immature skeleton. This review focuses on the primary and secondary imaging findings of ACL injuries in the pediatric patient and describes the most significant development-related changes that occur in the knee throughout childhood. TECHNICAL CONSIDERATIONS MR imaging (MRI) is the main modality for visualization of the ACL. Injuries are shown best by a combination of high-resolution, high-signal-intensity images, and water- sensitive images. In the past, proton density (also called intermediate-weighted) images have provided high anatomic detail, and T2-weighted images and short Tau inversion recovery images have provided sensitivity to edema or fluid. Fat-saturated, intermediate-weighted sequences are increasingly used, because they have both high resolution and sufficient water sensitivity to detect edema. High resolution images require at least 120 to 140 mm field of view, matrices above 256  256, and a slice thickness of 3 mm or less. Our protocol includes an intermediate-weighted and a T2-weigthed sequence with fat suppression in the sagittal plane. The intermediate- weighted images depict the fibers of the ACL, and the T2-weighted images show edema in cases of ligamentous injuries as well as associated bone bruising. 3 In the coronal and axial planes, fat-saturated intermediate-weighted images usually suffice. Department of Radiology, The Children’s Hospital of Philadelphia, 34th & Civic Center Boulevard, 3NW 17, Philadelphia, PA 19104, USA * Corresponding author. E-mail address: hov@email.chop.edu Clin Sports Med 30 (2011) 707–726 doi:10.1016/j.csm.2011.06.006 sportsmed.theclinics.com 0278-5919/11/$ – see front matter © 2011 Elsevier Inc. All rights reserved.