EQUINE VETERINARY EDUCATION / AE / MARCH 2015
131
Clinical Commentary
Equine temporomandibular joint (TMJ) disease: Professional polarity and caregiver bias
J. L. Carmalt Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada. Corresponding author email:
james.carmalt@
usask.ca
The paper by Jørgensen et al. (2015) in this issue is intriguing and raises a number of questions. The authors describe the case of a horse that was not performing as expected. There was lameness detected upon clinical examination and yet, at the owner’s insistence, intra-articular analgesia of the left temporomandibular joint (TMJ) was performed. Further examination under saddle resulted in a significant, albeit subjective, improvement in the movement of the horse. Lameness diagnosis resulted in localisation of the pain to the proximal suspensory ligament region. Diagnostic ultrasound of the suspensory ligaments and flexor tendons was performed and deemed to be within normal limits. Treatment of the lameness consisted of corrective farriery while the supposed TMJ inflammation (pain) was treated by intra-articular steroid injection. This author commends Jørgensen et al. (2015) for
publishing this report for several reasons. Firstly, they were willing to listen and act upon the concerns of the owner to the point that, to their surprise, a positive improvement was made following analgesia of the joint. This author is an inherent sceptic and as such he would probably have approached the post analgesia examination with negative bias; not so the authors of the manuscript. Further, they went on and performed a computed tomographic examination of the head to further characterise the pathology (if any) of the TMJs. An abnormality was detected and only upon receipt of this information did they medicate the offending joint. The final diagnosis was made upon the basis of a logical diagnostic work-up and the use of advanced imaging techniques which is laudable; a process that is all too often neglected in the diagnostic work-up of suspected disease of this joint (Carmalt 2014).
The problem, which Jørgensen et al. (2015) correctly
address, is that the decision-making process throughout the case was entirely subjective and hinged on unavoidable caregiver bias. The results of the intra-articular block were determined based on a riding examination by the very person that requested the diagnostic technique. As equine clinicians, the determination of lameness is often a subjective matter based on opinion and experience. We have all had to fight the feelings of bias when a particularly difficult client, horse (or both) present for examination and we hope beyond measure that the nerve block, performed at mortal risk to ourselves, works. In the situation described by Jørgensen et al. (2015), a horse was presented by a client who had a deep seated belief that the problem was in the TMJ. Imaging was performed, an abnormality detected and analgesia of the joint was then performed. Post analgesia, that same client rode the horse in front of the veterinarians (who had seen the CT images and
performed the diagnostic analgesia) and both parties determined that the performance of the horse had significantly improved. Denoix et al. (2003) illustrated this effect in a paper describing the use of using biphosphonates for the treatment of navicular disease in sport horses. He found significant caregiver bias in the control group in which 40% of owners in the sham-treated population initially believed their horses to have improved following treatment. This number dropped in the subsequent months in a manner typical of bias. This author does not doubt that there may have been a problem in this joint, or surrounding region and probably would not have followed the diagnostic procedures in a different fashion and yet the ultimate diagnosis is questionable. In the opinion of the author, our profession is extremely
polarised in their opinions on diseases of the TMJ. There are those that dismiss the possibility outright, those that believe that it may occur, but consider that the effects and prevalence of disease may be extremely limited and finally, others that feel that a significant number of horses have disease (or abnormalities) of this joint and are treating relatively indiscriminately. One only has to perform a quick internet search to find equine veterinary practices advertising the treatment of this condition, some even going as far as to say that it can be treated in a single injection. The overwhelming problem concerning this enigmatic joint
at present is the lack of scientific evidence for anything other than sepsis. Why? Given that this is an appendicular skeletal joint, one should see degeneration just as readily as with other similar joints. The problem is that there may not be other similar joints. The TMJ is unique and as such may not follow a recognised pattern of degeneration. This author routinely palpates the region surrounding the TMJs in every horse as part of his complete oral examination. So far, not a single horse has exhibited avoidance behaviour. This is concerning. Either the examination is not being performed properly, the test is not sensitive for the disease or the prevalence of disease is low. The diagnostic conundrum is what does one do if a positive is found? What does it mean? So far, the only evidence upon which to base action is a paper describing several cases of avoidance behaviour which were ameliorated by correcting incisor malocclusions (May 1996). Incisor malocclusions are, however, relatively common, whereas supposed pain on palpation of the periarticular region is not. The author does not perform diagnostic imaging of the
TMJs of these ‘nonresponding’ horses and it may be that disease is present and remains undiagnosed. However, in the report by Jørgensen et al. (2015), advanced imaging techniques were used and a morphological abnormality within the suspected joint was found. Once again, however,
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