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

Two middle-aged, unrelated cocker spaniels were investigated for apparent jaw pain and slowly progressive restriction of mouth opening, in the absence of previous trauma or jaw-locking episodes. Computed tomographic evaluation was suggestive of a dynamic impingement between the coronoid process of the mandible and the medial surface of the zygomatic arch, trapping the temporalis muscle. Bilateral, single-session, partial resection of the coronoid process and zygomatic arch resulted in complete resolution of the clinical signs. This form of impingement should be considered when evaluating cases with a mechanically restricted, painful opening of the mouth.