Traumatic focal myositis of the temporalis muscle due to presumptive impingement between the zygomatic arch and coronoid process in two cocker spaniels with restricted mouth opening.

Consider coronoid-zygomatic impingement in cocker spaniels with restricted mouth opening.

This case series describes a novel presentation of temporalis muscle myositis in two middle-aged cocker spaniels characterized by progressive mouth opening restriction and jaw pain without preceding trauma. Computed tomographic imaging revealed dynamic impingement of the temporalis muscle between the coronoid process of the mandible and the medial zygomatic arch. This anatomical entrapment mechanism had not been previously documented as a cause of restricted jaw opening in dogs. Both cases were successfully managed through bilateral partial coronoid process and zygomatic arch resection performed in a single surgical session, resulting in complete clinical resolution. The authors propose that this form of mechanical impingement should be considered in the differential diagnosis of canine temporomandibular disorders presenting with painful, mechanically restricted mouth opening. The condition may represent a breed-specific anatomical predisposition in cocker spaniels. This work expands understanding of uncommon causes of masticatory dysfunction in companion animals and provides a surgical treatment protocol for this previously unreported condition.

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