The effect of acute unilateral inflammation of the equine temporomandibular joint on the kinematics of mastication.
Authors: Smyth T T, Carmalt J L, Treen T T, Lanovaz J L
Journal: Equine veterinary journal
Summary
# Editorial Summary Temporomandibular joint disease remains poorly understood in equines compared to other species, with limited knowledge of how pathology affects mastication mechanics. Smyth and colleagues induced acute unilateral TMJ inflammation in six horses using lipopolysaccharide injection, then tracked mandibular kinematics during hay consumption via optical motion capture before and 6 hours post-injection. Four horses developed joint effusion; notably, all animals that were originally performing the power stroke on the injected side switched to the contralateral side, whilst those injected contralaterally maintained their pattern—a clear avoidance behaviour. Vertical opening of the mandible reduced significantly across all horses, and whilst total rostrocaudal movement remained unchanged, its timing within the chewing cycle shifted substantially; lateral mandibular movement was unaffected. These findings indicate that even transient TMJ inflammation triggers adaptive masticatory strategies and feed inefficiency (evidenced by quidding in two cases), with important implications for practitioners: changes in chewing pattern may indicate subclinical TMJ pathology, and recognition of these compensatory mechanisms is essential for early diagnosis and management of joint disease before secondary dental wear or nutritional compromise occurs.
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Practical Takeaways
- •Horses with TMJ inflammation preferentially switch their chewing to the opposite side to avoid pain, which can be observed clinically as a change in mastication pattern
- •TMJ disease impairs jaw opening and feed efficiency; clinicians should monitor for reduced vertical jaw motion and quidding as clinical indicators of TMJ problems
- •Horses continue to eat despite TMJ inflammation through compensatory mechanisms, so absence of anorexia does not rule out significant TMJ pathology
Key Findings
- •LPS injection into the TMJ caused 4 of 6 horses to develop joint effusion and 2 horses to begin quidding
- •All horses injected on the original power stroke side switched to contralateral side mastication, while 2 injected on contralateral side did not switch
- •All horses developed reduced vertical mandibular opening (vertical pitch) following TMJ inflammation
- •Lateral mandibular movement was unaffected by LPS injection despite altered rostrocaudal timing within the masticatory cycle