Increased or Normal Mouth Opening with Locked Jaw
An 18-year-old patient presented to the emergency room with a TMJ open lock condition. He gave a history of recurrent open locks during range of motion movements multiple times during the last 3 months, all of which were self-reducible. A CT scan was obtained and the patient was diagnosed as having a TMJ dislocation. The “dislocated mandible was reduced” under intravenous sedation by the ER physician. He was then referred to a specialist for follow-up.
The clinician failed to diagnose the condition appropriately. The history of recurrent yet “self-reducible” open locks should have alerted the physician that the etiology was unlikely to be dislocated condyle out of the fossa and trapped anterior to the
Fig. 3.4 (a) CT scan demonstrating true condylar dislocation with the mandibular condyle displaced beyond the anatomic limits of the glenoid fossa and is trapped anterior to the articular eminence. (b) CT scan showing that the mandibular condyle remains within the anatomic limits of the glenoid fossa and is not trapped anterior to the articular eminence
eminence. The CT scan obtained at the time of the locking (Fig. 3.4b) reveals that the condyle was not dislocated out of the fossa.
Open lock may be the result of either dislocation of the condyle (Fig. 3.4a) or a disc- condyle issue. In the former, there is usually hypermobility with steep articular eminence where the condyle gets trapped anterior to the fossa on wide opening, while in the latter, the condyle stays in the fossa (Fig. 3.4b) but translates anterior to the disc, which prevents closure.
In TMJ condylar dislocation, the condyle is anterior and superior to the articular eminence on CT scan, and this condition is often accompanied by spasm of the muscles of mastication. Dislocation can be classified into acute or chronic, partial or complete, dislocation. Acute cases are typically managed by manual reduction and analgesics. On the other hand, chronic dislocation is managed by different nonsurgical and surgical options. Surgical treatment generally aims at either augmenting (to prevent dislocation) or removing the mechanical obstacle (to allow self-reduction).
In contrast to this scenario, there are some patients where the open lock condition occurs within the expected range of condylar motion . In these cases, the occurrence of open lock is often spontaneous, and usually there is no associated history of joint laxity, neurologic disorders, and other factors that predispose to condylar dislocation . On radiographic examination, the eminence is shallow and the condyle is located inferior to rather than in front of and superior to the eminence (Fig. 3.4b). The obstruction, which is not visible in plain radiographs or CT scans, may be demonstrated on TMJ MRI scans (esp. dynamic cine MRI) which show that the condyle is located in front of the anterior band of the disc in an open lock position and is unable to return posteriorly into the fossa due to mechanical obstruction by the disc. These cases can usually successfully be managed by arthrocentesis or disc-related surgical procedures.