Case report highlights surgical cause of restricted jaw opening

Two cocker spaniels with jaw pain and restricted mouth opening were diagnosed with a likely mechanical cause that may be easy to miss on routine workup: dynamic impingement of the temporalis muscle between the mandibular coronoid process and the zygomatic arch. In the new Journal of Small Animal Practice case report, the dogs were found to have traumatic focal myositis of the temporalis muscle associated with that impingement, and both were treated surgically with partial resection of the coronoid process and zygomatic arch, resulting in complete clinical resolution. The report adds a new, highly specific differential for dogs presenting with trismus or painful reduced jaw excursion, especially when standard explanations such as temporomandibular disease or generalized masticatory muscle myositis don’t fully fit. (eurekamag.com)

Why it matters: For veterinary professionals, the main takeaway is diagnostic. Restricted mouth opening in dogs is often worked up through the lens of immune-mediated masticatory muscle disease, temporomandibular pathology, trauma, or fracture sequelae, but prior veterinary reports have also shown that coronoid-zygomatic interference can create dynamic jaw locking or impingement. This case series suggests CT, and especially attention to dynamic anatomic relationships around the coronoid process, may help identify focal mechanical lesions that are surgically correctable and could otherwise be mistaken for primary inflammatory myopathy alone. (pmc.ncbi.nlm.nih.gov)

What to watch: Watch for whether this anatomic mechanism is recognized in more breeds, and whether future reports clarify when CT-based diagnosis should prompt earlier referral for maxillofacial surgery. (eurekamag.com)