Horses that are subjected to extensive or who do not receive regular dental maintenance are at a higher risk of developing TMJ dysfunction. Horses with vices such as cribbing or wood chewing may cause damage to their teeth which can affect the motion of the TMJ, or those vices may cause subluxation of the TMJ resulting in dysfunction. Aggressive riders and drivers may also augment the function of the TMJ by spraining the collateral ligaments of the TMJ, allowing the joint to become unstable, and predisposing to degenerative joint disease. Horses with chronic often attempt to balance themselves by leaning on one side of the bit. In doing so they may damage the structures of the TMJ. The clinical signs and symptoms of TMJ dysfunction are varied and may make it difficult to recognize. Clinical signs and symptoms include reluctance to be bridled, misalignment of the teeth, asymmetry of the masseter and temporalis muscles, , weight loss, reluctance to bend in one direction, reluctance to flex the head and neck, teeth grinding, resistance to the bit on one side of the mouth, and rearing or head tossing when pressure is applied to the bit. Generally, diagnosis is made through clinical signs and symptoms alone though radiography, CT scan, ultrasound or arthroscopic exploration of the joint may reveal the structures involved and the extent of the damage to joint structures. Treatment depends on the clinical presentation, and may include chiropractic adjustment, NSAID’s, surgical debridement of the joint, and massage including trigger point therapy and facial release to the temporalis and masseter muscles. Prognosis for horses affected by TMJ dysfunction is guarded as TMJ dysfunction is a form of degenerative joint disease.
Occipital Subluxation
Occipital subluxation is the clinical manifestation of the subluxation of the joint (OA joint). , as is seen when a horse rears and hits its head on a low ceiling or when it flips over backwards and hits its head on the ground. A horse may also injure the OA joint if it steps on the reins or a lead while in flight. Generally it is caused by acute trauma to the When there is trauma to the nuchal crest the skull is forced downwards while the neck muscles resist the force, pushing the atlas and the rest of the cervical vertebrae upwards. This causes sprain of the ligaments that support the OA joint as well as strain of the , muscles. Horses that are head shy, or those prone to rearing or head tossing are more likely to sustain injuries that may result in occipital subluxation.
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