RADIOGRAPHIC TECHNIQUE AND ANATOMY OF THE EQUINE SACROILIAC REGION DANIELA GORGAS,PATRICK KIRCHER,MARCUS G. DOHERR,GOTTLIEB UELTSCHI,JOHANN LANG Radiography is part of evaluating horses with poor performance and pelvic limb lameness; however, the radiographic appearance of the sacroiliac region is poorly described. The goal of the present study was to describe the use of a simple technique to obtain radiographs of the sacroiliac region in the anesthetized horse and to describe the radiographic appearance of this region. Seventy-nine horses underwent radiography of the pelvis under general anesthesia in dorsal recumbency. During a 5s exposure time the horse was actively ventilated to blur the abdominal viscera, which allowed assessment of individual bone structures in 77 horses. A large variation in the shape of the sacral wings, their articulation with the transverse processes of L6, and the relation of the sacrum to the ilium were observed. Females had significantly narrower width of the sacral wings. Broad sacral wings and bony proliferations at the caudal aspect were commonly observed features and their size was highly correlated with gender. In males, caudal osteophytes were significantly larger than in females. Five horses had transitional or hemitransitional vertebrae. Radiography with the ventilation-induced blurring technique is a simple approach that results in diagnostic quality radiographs and delineation of the highly variable bone structures of the sacroiliac region. Veterinary Radiology & Ultrasound, Vol. 48, No. 6, 2007, pp 501–506. Key words: horse, motion-induced blurring, radiography, sacroiliac joint. Introduction P ROLONGED POOR PERFORMANCE, back stiffness, and hind limb lameness in horses may be due to chronic sacro- iliac disease, of which little is known. Chronic sacroiliac disease has been categorized into sacroiliac osteoarthritis and sacroiliac desmitis. 1 Osteoarthritic changes at the sa- croiliac joint and the lumbosacral and lumbar intertrans- verse joints are common and were seen in 36 of 36 Thoroughbred racehorses. 2 The clinical diagnosis of sa- croiliac joint disease is imprecise as the signs are nonspe- cific and confirmation by intraarticular injection of analgesics is hindered by the inaccessibility of the joint. 3–5 Diagnostic imaging is helpful in the assessment of suspect- ed sacroiliac disease. Diagnostic quality radiographs are difficult to obtain because of superimposition of the large muscles and bowel over the sacroiliac region, and only a limited number of projections can be obtained. 6–9 To over- come these limitations, linear tomography has been pro- posed as the imaging modality of choice but the availability of equipment and examination time required have limited the clinical application of this method. 10,11 Our aim is to present a simple technique to obtain di- agnostic sacroiliac radiographs in the anesthetized horse, to describe the normal radiographic appearance of the sacro- iliac region, and to describe the relationship of the findings to gender, body weight, and age. Material and Methods Seventy-nine horses (age range 4–20 years, mean 10.3 years) undergoing pelvic radiography because of lameness or poor performance between January 2004 and January 2006 were studied. There were 75 warmblood horses (44 males, 31 females, mean body weight 562 kg) and four pure bred horses (two females/two males; mean body weight 474 kg). All horses were under general anesthesia incorporating intubation after induction and maintenance with a mixture of isoflurane and oxygen. 12 Computed radiographs à were made using a Siemens Polydoros SX 80 generator (400V) with a Siemens Tridoros X-ray tube (V: 1200 kW)w and a grid (6:1 grid ratio). After positioning the horse in dorsal recumbency with the limbs flexed in a neutral position, the X-ray beam was centered on the midline at the level of the tubera sacralia with a focus-to-film distance of 130 cm. Settings of 96kV and 500 mAs over an exposure time of 5 s were chosen during which the anesthetist actively ventilat- ed the horse to cause movement and radiographic blurring of superimposed intestinal structures. The findings of this study were presented at the IVRA/ACVR 2006 joint scientific meeting, Vancouver. Address correspondence and reprint requests to Dr. Daniela Gorgas, at the above address. E-mail: daniela.gorgas@kkh.unibe.ch Received October 30, 2006; accepted for publication April 9, 2007. doi: 10.1111/j.1740-8261.2007.00287.x From the Divisions of Clinical Radiology (Gorgas, Kircher, Ueltschi, Lang) and Clinical Research (Doherr), Department of Clinical Veterinary Medicine, Vetsuisse Faculty, University of Bern, Bern, Switzerland. à Fuji FCR 5000, FUJIFILM Madical AG, Dielsdorf, Switzerland. wSiemens Schweiz AG, Zu¨ rich, Switzerland. 501