A COMPLEMENTARY RADIOGRAPHIC PROJECTION OF THE EQUINE TEMPOROMANDIBULAR JOINT ALESSIA J. EBLING,ALEXIA L. MCKNIGHT,GABRIELA SEILER,PATRICK R. KIRCHER The complexity of the equine skull makes the temporomandibular joint a difficult area to evaluate radio- graphically. The goal of this study was to determine the optimal angle for a complementary radiographic projection of the equine temporomandibular joint based on a computed tomography (CT) cadaver study. CT was performed on six equine cadaver heads of horses that were euthanized for other reasons than temporo- mandibular joint disease. After the CT examination, 3D reconstruction of the equine skull was performed to subjectively determine the angle for a complementary radiographic projection of the temporomandibular joint. The angle was measured on the left and right temporomandibular joint of each head. Based on the measure- ments obtained from the CT images, a radiographic projection of the temporomandibular joint in a rostra- l451ventral-caudodorsal oblique (R451V-CdDO) direction was developed by placing the X-ray unit 301 laterally, maintaining at the same time the R451V-CdDO angle (R451V301L-CdDLO). This radiographic projection was applied to all cadaver heads and on six live horses. In three of the live horses abnormal findings associated with the temporomandibular joint were detected. We conclude that this new radiographic projection of the tem- poromandibular joint provides superior visualization of the temporomandibular joint space and the articular surface of the mandibular condyle. Veterinary Radiology & Ultrasound, Vol. 50, No. 4, 2009, pp 385–391. Key words: computer tomography, CT, equine temporomandibular joint, mandibular condyle, radiography. Introduction T HE FEW REPORTS of temporomandibular joint disease in horses include degenerative changes, septic arthri- tis, 1–6 luxation, 7,8 fractures, 4,9,10 and experimental con- dylectomy. 11 There is a strong relationship between dental disorders and temporomandibular disease. 12–15 Reports of equine temporomandibular disease may not be more nu- merous because of the nonspecific nature of clinical signs 9 and difficulty in imaging temporomandibular joint radio- graphically. 2 Recommended radiographic views of the temporoman- dibular joint consist of a left and right lateral, a ven- trodorsal (VD), a dorsal601lateral-ventrolateral oblique (D601L-VLO) view or a modification of the latter. 16,20 Lesions which were most likely diagnosed with radiogra- phy include temporomandibular joint luxation 7,8 and frac- tures of the mandibular condyle. 4,9 The complexity of the equine skull, and superimposition of structures, make the temporomandibular joint a difficult area to evaluate radiographically. 17–21 We have been assessing a complementary radiographic projection, which allows superior visualization of the equine temporoman- dibular joint, especially the mandibular condyle. However, the exact X-ray beam angle for this view is uncertain, and therefore this radiographic projection was not reproducible in different horses. The objective of this study was to de- termine the optimal angles for a complementary diagnostic radiographic projection of the equine temporomandibular joint based on a computed tomography (CT) cadaver study. Materials and Methods CT was performed on 12 temporomandibular joints of six horses, which were euthanized for reasons other than temporomandibular joint problems. There were three Thoroughbreds, one Standardbred, one Quarterhorse, and one Paint horse. Five horses were geldings and one was a mare. Age ranged between 3 and 13 years, with a median of 5. CT imaging was performed using a third-generation he- lical CT scanner. Ã Each equine head, was scanned from the level of the fourth premolars to the most caudal aspect of the external occipital protuberance. A transverse helical image series with a collimation of 5mm and a pitch of 1.4 was acquired using an exposure of 140 kV, 160 mA, and 1 s. Address correspondence and reprint requests to Dr. Patrick R. Kircher, at the above address. E-mail: patrick.kircher@knp.unibe.ch Received July 1, 2008; accepted for publication December 26, 2008. doi: 10.1111/j.1740-8261.2009.01554.x From the Section of Sports Medicine and Imaging, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, 3900 Delancey Street, Philadelphia, PA 19104-6010 (Ebling, McKnight, Seiler, Kircher), Section of Clinical Radiology, Vetsuisse Faculty Bern, Univer- sity of Bern, La¨ nggassstrasse 128, Postfach 8466, 3001 Bern, Switzerland (Ebling, McKnight, Seiler, Kircher), and Section of Diagnostic Imaging, Vetsuisse Faculty Zu¨ rich, University of Zu¨ rich, Winterthurerstrasse 204, 8957 Zu¨ rich, Switzerland. Ã Pro Speed, General Electric Medical Systems, Milwaukee, WI. 385