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EQUINE VETERINARY EDUCATION / AE / MARCH 2015
Fig 2: Injection site for TMJ arthrocentesis.
resenting girth area palpation. No signs of lameness were evident. At one year follow-up, the rider reported that the horse was still performing very well. Competition results retrieved that from the Danish Riding Association’s web page indicates the horse is performing at a higher level with better scores after treatment compared with before when evaluated subjectively.
Discussion
The TMJ is a complex diarthrodial joint between the caput of the condylar process of the mandible and the base of the zygomatic process of the temporal bone. The incongruence of the 2 articular surfaces is compensated by an articular biconcave fibrocartilage disc (meniscus). The joint is supported by a lateral and a caudal ligament (Rodriguez et al. 2006). The TMJ consists of 2 compartments, the dorsal and ventral, the latter divided into a rostral and caudal pouch. The caudal pouch is very close to the temporohyoid articulation of which the clinical relevance is unknown (Rosenstein et al. 2001; Rodriguez et al. 2006, 2007). The dorsal and ventral compartments do not appear to communicate (May et al. 2001; Rodriguez et al. 2006), although one previous cadaver study showed communication (Rosenstein et al. 2001). The parotid salivary gland is in close proximity to the joint and may overlie the caudal part of the joint (May et al. 2001; Rosenstein et al. 2001). Furthermore, many vascular and neural structures are in very close proximity to the TMJ (Rodriguez et al. 2006). The anatomy of the TMJ has been previously investigated using ultrasonography (Weller et al. 1999b; Rodriguez et al. 2007), arthroscopy (May et al. 2001; Weller et al. 2002), CT (Rodriguez et al. 2008) and MRI (Rodriguez et al. 2010). Different disease processes of the equine TMJ have been
previously described in the literature, predominantly with traumatic causes such as septic arthritis (Warmerdam et al. 1997; Weller et al. 1999a; Carmalt and Wilson 2005; Nagy and Simhofer 2006; Barnett et al. 2014), fractures and luxations (Devine et al. 2005). Neoplasia with a squamous cell carcinoma invading a TMJ in a horse has been reported
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(Perrier et al. 2010). Dental disease as a result of incisor abnormalities and excessive use of mouth gags have been speculated to be associated with OA of the TMJ (May 1996; Wintzer 1997; Baker 2002). In the investigation of TMJ disease, MRI and CT are
probably the gold standard (Warmerdam et al. 1997), but not always the first choice, as these procedures require expensive equipment and in many cases general anaesthesia of the horse. Standing head CT scanning is becoming more readily available and affordable in equine clinics worldwide. Radiographic evaluation of the TMJ is possible, but due to the superimposition of adjacent osseous structures, the best diagnostic images are obtained with technically challenging oblique and tangential projections (Ebling et al. 2009; Townsend et al. 2009). Using ultrasonography, longitudinal images of the TMJ from rostral, lateral and caudal approaches can be obtained to evaluate the joint (Rodriguez et al. 2007). In diagnosing TMJ disease, scintigraphy is of little help as it only determines the location of a problem (with increased bone/cellular turnover), but gives no information on the disease process (Weller et al. 1999a). Reports on cases of equine TMJ disorders are uncommon
(Carmalt 2014), but this may only relate to the difficulties in diagnosing disease, rather than a true low prevalence of TMJ disorders. In the present case, it would have been very easy to simply attribute the performance problems to the left front lameness as veterinary training is largely centred around the recognition of lameness, particularly in performance problems in horses. In this case, further investigation was performed at the owner’s insistence and this allowed detection of a TMJ disorder. So how many of these do we overlook in our daily clinical work? The answer is of course unknown and the authors wish to draw attention towards TMJ pathology as a possible cause of reduced performance in equine athletes. Studies on the biomechanical relationship between TMJ,
mastication and dental health are lacking (Ramzan 2006; Carmalt 2007) and the exact reasons why horses develop TMJ OA still remain unclear. Nevertheless, dental abnormalities such as overgrowths, hooks and ramps have been incriminated as a cause of TMJ OA, but may also be the result
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