There’s been increasing interest in recent years in the horse’s temporomandibular (jaw) joint, also known as the TMJ. TMD — or temporomandibular dysfunction — has been blamed for a host of problems, including behavior issues, bridle resistance, back pain, poor gaits, poor performance, even cribbing. It’s been suggested that any horse that doesn’t graze extensively, or has ever had a bit in its mouth or worn a noseband may well be suffering from TMD as a result. Interest in the jaw and in TMD has even given birth to a specialty within the massage ranks.
An integral component of TMD is dental abnormalities. Since TMD is alleged to both cause, and be caused by, dental problems, any horse with TMD would also have dental abnormalities. If you string all these risk factors together, they would apply to virtually every horse. Is this really an unrecognized epidemic problem’
Fact is, there are few true veterinary reports of problems related to the jaw. Most of the cases are fractures and infections. TMD is described as an arthritic process that could eventually wear away the joint cartilage in the jaw.
Several presentations regarding the TMJ were given at the 2002 meeting of the American Association of Equine Practitioners. While it was concluded that some headshaking, resistance and quidding have responded to local anesthesia of the TMJ, and that problems may be underdiagnosed, it was stated that most problems are related to trauma and infection.
Equally important — and largely ignored in the current wave of blaming the jaw for assorted problems — is the issue of diagnosis. The TMJ is a joint and not difficult to enter to sample joint fluid and inject local anesthesia to see if the problem in question improves. Severely arthritic joints will show bone changes on X-ray. Inflammation is detectable on joint fluid analysis. Bone scanning is expensive but reliable, and ultrasound can be used to detect soft-tissue problems. None of these things are routinely being done in horses that are labeled as suffering from TMD.
One thing everyone agrees upon is that dental pathology and jaw problems may go hand in hand. Researchers at the Western College of Veterinary Medicine in Saskatchewan decided to do a study (Journal of Veterinary Dentistry, June 2006) to see if they could confirm that assumption by looking at the levels of cytokines, markers of inflammation, in the TMJs of horses of varying ages and with varying types of dental problems. The pattern of cytokine changes in arthritic/inflammed equine joints has been well described. They found a trend, although not significant, for the levels of only one cytokine to increase with age, but no differences in cytokine levels in the TMJ as a result of dental pathology scores. Levels of the inflammatory cytokines that are very sensitive markers of joint disease of all types were no different.
Undiagnosed TMJ problems probably exist. If your horse has been suggested to have a TMJ problem, check it out the right way with joint fluid analysis and joint anesthesia as a first step before you embark on a host of treatments the horse may very well not need.