Post-traumatic severe trismus caused by impairment of the masticatory muscle

Restriction of the mouth opening from a pathologic condition outside the temporomandibular joint is called a pseudo- or extra-articular ankylosis. The authors report two cases of severe post-traumatic pseudoankylosis. One case showed fibrous degeneration of the bilateral masseter muscles without a facial bone fracture, which caused severe trismus, a mouth opening of less than 2 mm, and gradually appeared after blunt injuries to the face. The other was a rare case accompanied with the bone formation in the masseter muscle and was diagnosed as myositis ossificans traumatica, which also presented as severe trismus, with a maximal mouth opening of 5 mm after facial violence. Both were surgically treated with dissection of the affected muscles. In addition, a hemicoronoidotomy was performed in the case of myositis ossificans traumatica. Although a conservative therapy with physical rehabilitation is the basic policy for the management of pseudoankylosis of the temporomandibular joint, a surgical treatment should be considered when the origin of the problems is an osteogenic character or severe extra-articular ankylosis resistant to conservative therapy before completion of true temporomandibular joint ankylosis.