Dog Positioning for CT Scanning
World Small Animal Veterinary Association World Congress Proceedings, 2015
L. Seng Fong
Department of Veterinary Clinical Studies, Faculty of Veterinary Medicine, Universiti Putra Malaysia, Putra, Malaysia

In comparison to diagnostic modalities such as conventional radiography, ultrasonography, and magnetic resonance imaging, computed tomography (CT) is a more accurate tool for diagnosing elbow joint disease, particularly for medial coronoid disease (MCD). Its ability of interpreting the images in different reconstructive views and planes allows CT to be superior to conventional radiography because there is no distraction of superimposed images. Lesions involved in elbow joint diseases such as displaced mineralized fragments of the medial coronoid process, signs of radioulnar incongruence (RUI), and the presence of subtrochlear notch sclerosis are easy to detect using CT (Cook, Cook 2009).

In a previous study (Lau et al. 2013), we followed the development of MCD by using both radiography and CT. CT had the higher sensitivity (30.8%) in comparison with radiography (0%) in detecting incipient MCD. In that particular study, the dogs were anesthetized and positioned in dorsal recumbency on the CT scanning table with the elbow joints extended approximately 135°. The antebrachia were positioned parallel to each other and as symmetrically as possible at the same level using a custom-made positioning device. Transverse views, perpendicular to the antebrachia, were made with a third-generation single-slice helical CT scanner (Philips Secura, Philips) using 120 kV and 120 mA with an exposure time of 1000 ms. One millimeter thick slices of the elbow joints were made with the joints in neutral position. The earliest signs of MCD were detected by using CT at 14 weeks with a mineralized bone fragment detected at the base of the MCP subchondral bone, which did not extend to the apex of the MCP.

By using CT, other entities of elbow dysplasia, namely, ununited anconeal process (UAP) and osteochondrosis lesions are best seen on sagittal and dorsal plane reformatted images as either a partial or complete hypoattenuating line and as lucency or flattening of the medial aspect of the humeral condyle with surrounding subchondral bone sclerosis (Reichle, Snaps 1999). Different positioning with the elbow either in in supination or pronation, extension and standing angle (135°) are more critical in evaluating RUI (Murphy et al. 1998; Wagner et al. 2007). Maximal supination and pronation of the antebrachium leads to a significant variation in measurements of the radioulnar joint space; hence, a neutral position of the antebrachium during scanning is critical to detect RUI. On joint extension (160°), there would be a cranial translation of the ulna, increasing the space between the radius and ulna at the ulnar incisures (Wagner et al. 2007). Reconstructed images from dorsal and sagittal planes are useful for accurately determining incongruity of the radius and ulna (Reichle et al. 2000). The most reliable reconstruction plane is the mid-coronoid oblique plane, because it allows the most accurate measurement of radioulnar congruence (Holsworth et al. 2005).

Despite of its great advantages, CT does have certain limitations. It cannot be used to assess cartilage integrity and the animals are not in weight bearing position during the examination. These disadvantages mean that it is not possible to detect or assess pathological changes in cartilage and make it more difficult to determine the congruity of the elbow joints. The physiological incongruity of the elbow joints during movement also could not be detected.


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Speaker Information
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L. Seng Fong
Department of Veterinary Clinical Studies
Faculty of Veterinary Medicine
Universiti Putra Malaysia
Putra, Malaysia

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