Normal and Variant Anatomy of the Elbow on Magnetic Resonance Imaging Joel M. Stein, MD, PhD*, Tessa S. Cook, MD, PhD, Stephanie Simonson, MD, Woojin Kim, MD Magnetic resonance imaging (MRI) provides excel- lent delineation of the bones of the elbow and the surrounding soft tissue structures. The compo- nents of the elbow can be divided into osseous structures, the joint capsule and ligaments, muscles and tendons, and nerves. In this article, the authors review the normal anatomy and the appearance of these structures on MRI as well as the anatomic variants that should be recognized and distinguished from pathologic entities. PROTOCOL Axial, coronal, and sagittal images are acquired using T1- and T2-weighted images (Table 1). The axial images must include the radial tuberosity where the biceps tendon attaches. Typically, patients are placed in supine position with the arm to their side, and as a result, excellent field homogeneity is required for off-center fat suppres- sion. Although the patient can alternatively be positioned prone with the arm extended overhead, this position is less well tolerated and can also introduce motion degradation artifact. The distal biceps brachii tendon takes an oblique course and is therefore susceptible to partial volume- average effects and difficult to visualize on a single image. The extent of the tendon can be better imaged with the flexed abducted supinated view, whereby the elbow is flexed with the shoulder abducted and the forearm in supination (Fig. 1). 1 OSSEOUS STRUCTURES The elbow joint is composed of three bones (humerus, radius, and ulna) that form three articu- lations (ulnohumeral, radiohumeral, and radioul- nar) within a common joint capsule. The ulnohumeral and radiohumeral articulations allow for flexion and extension of the forearm. The radio- humeral and radioulnar articulations permit prona- tion and supination of the forearm. The tubular shaft of the humerus flares distally to form the medial and lateral condyles. As the condyles sweep outward, they form paired bony protuberances, the medial and lateral epicondyles, that serve as attachment sites for ligaments and tendons. The most distal aspects of the condyles are the articular surfaces, the medial trochlea and lateral capitellum. The trochlea is the more central and larger of the two and is shaped like a pulley with central concavity and flared margins. The trochlea articulates within the crescent troch- lear notch along the anterior surface of the prox- imal ulna, forming a hinge joint that permits flexion and extension. The proximal aspect of the trochlear notch is formed by the olecranon, whereas the distal aspect is the coronoid process. This work was not supported by any funding agency. Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce Street, 1 Silverstein, Philadelphia, PA 19104, USA * Corresponding author. E-mail address: joel.stein@uphs.upenn.edu KEYWORDS  Normal elbow anatomy  Elbow magnetic resonance imaging  Normal variants Magn Reson Imaging Clin N Am 19 (2011) 609–619 doi:10.1016/j.mric.2011.05.002 1064-9689/11/$ – see front matter Ó 2011 Elsevier Inc. All rights reserved. mri.theclinics.com