598


NOVEMBER 2022


veterinarians, with 70% using it sometimes. When a sufficiently powerful generator is unavailable, the use of radiography is frequently restricted to imaging of the spinous processes (Vandeweerd, 2015). Conversely, ultrasonography is a more versatile diagnostic tool that can be used to detect soft tissue lesions (supraspinous ligament desmitis, thoracolumbar fasciitis, myositis), as well as APJ lesions, with a high sensitivity to detect bone remodelling and osteophyte formation (Audigi


e et al., 2013; Denoix, 1999). In


addition, using ultrasonography, APJ lesions can be identified in the caudal lumbar region, an area where APJs are difficult to visualise on radiographs, even with high- output x-ray machines, because of the large muscle mass in this area and the projection of the tuber coxae (Cousty et al., 2010; Denoix, 1999; Denoix & Dyson, 2011). Finally, ultrasonography is the only modality that definitively identifies the most affected side (if one is greater than the other), allowing better correlation with clinical signs and improving the efficacy of directed treatment such as ultrasound-guided injections. Of note, the clinical significance of asymmetry alone is not clear as 83% of euthanised Thoroughbred racehorses had asymmetry of at least one lumbar APJ in one retrospective post-mortem study (Haussler et al., 1997). Such asymmetry may, however, impair the biomechanical behaviour of the intervertebral joints and could predispose to the development of degenerative joint disease (Denoix, 1999). Limitations of ultrasonography in imaging the APJs are


twofold. First, unlike radiography, the ventral part of the joint cannot be visualised and bone density changes cannot be assessed, although densification of the subchondral bone (sclerosis) or its demineralisation (osteolysis) are other osteoarthritis-associated changes. Second, for anatomical reasons, the lumbar APJs (more prominent and closer to the skin surface) are much easier to image than the middle thoracic APJs (superimposed and deeper because of the length of the spinous processes). These limits are relative since a retrospective study (Cousty et al., 2010), revealed that periarticular bone proliferation of the APJ was more prevalent and more severe in a group of Standardbred French Trotters showing signs of back pain than in the control group, which was not the case for subchondral bone sclerosis. This finding suggests that periarticular new bone proliferation, which can be assessed by ultrasound, maybe more correlative with clinical signs of back pain compared to changes in bone density. In addition, APJ osteoarthritis is more frequently located in the thoracolumbar area (Cousty et al., 2010; Denoix, 1999; Girodroux et al., 2009) and cranial lumbar area (Denoix, 1998b, 1999). In the study from Cousty et al. (2010), osteoarthritis-associated lesions of the APJs were most frequently observed between T17 and L2 with the highest frequency in T18-L1 on Standardbreds, while Warmbloods and Thoroughbreds were mostly affected between T16 and L1, with the highest frequency in T16-T17 (Girodroux et al., 2009). The highest mobility of the thoracolumbar region may explain the preferred location of these lesions along the back (Denoix, 1999; Mespoulhes, 2002). Nevertheless, the clinical significance of these lesions seems to be different according to the breed and discipline. Lesions are indeed more severe in racing Thoroughbreds than in racing Standardbred French Trotters for whom mild lesions lead to discomfort and irregular gaits at high speed.


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Conclusion


Ultrasonography is a safe imaging technique that can be successfully performed in the field with regular practice for the diagnosis of APJ lesions in the thoracolumbar area. With sufficient anatomical knowledge and appropriate technique, this procedure provides accurate and real-time diagnostic information in the caudal thoracic and lumbar vertebral areas. Used alone or in combination with other imaging modalities, ultrasonography of the APJs improves the diagnosis and localization of the source of equine back pain, providing valuable information that can improve treatment and management of affected horses.


Authors’ declaration of interest No conflicts of interest have been declared.


Ethical animal research Not applicable to this article.


Source of funding


The authors thank the Normandy Regional Council and the European Regional Development Funds for their financial support.


Authorship


The study design was made by A. Beaumont. The study execution and image acquisition were made by all authors. A. Beaumont and L. Bertoni prepared the manuscript. All authors gave their final approval of the manuscript.


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