Temporomandibular joint (TMJ) dislocation can be classified into four groups (anterior, posterior, lateral, and superior) depending on the direction of displacement and the location of the condylar head. All the groups are rare except for anterior dislocation. ‘Inverse’ TMJ dislocation is a bilateral anterior and superior dislocation with impaction of the mandible over the maxilla; to the authors’ knowledge only two cases have previously been reported in the literature. Inverse TMJ dislocation has unique clinical and radiographic findings, which are described for this case.
Dislocation of the temporomandibular joint (TMJ) represents 3% of all reported dislocated joints in the body. Typical dislocation of the TMJ occurs when the mandibular condyle is displaced anteriorly beyond the articular eminence. TMJ dislocation has been classified in different ways, in 1832, Sir Astley Cooper proposed principles for the diagnosis and treatment of dislocation of the lower jaw. He introduced the terms complete dislocation (luxation) and imperfect dislocation (subluxation). Subluxation is defined as a displacement of the condyle out of the glenoid fossa and anterosuperior to the articular eminence, which can be reduced by the patient (self-reduced). It has been estimated that 70% of the population can subluxate the TMJ. In contrast, luxation is a similar displacement of the condyle that cannot be self-reduced .
Some authors base their classification on the direction of displacement and the location of the condylar head, defining four groups: anterior, posterior, lateral and superior dislocation. All the groups, except anterior dislocation, are rare, and one or both mandibular condyles can be affected . TMJ dislocations can also be classified into acute, chronic (prolonged) and recurrent .
The authors report a case of an ‘inverse’ TMJ dislocation in which the mandibular condyles were displaced bilateral, anterior and superior with impaction of the mandible over the maxilla. This rare TMJ dislocation has unique clinical and radiographic characteristics.
A 17-year-old man who had been involved in a low speed motor vehicle accident presented to the emergency unit of Zacamil’s national hospital. He had been thrown from the bed of a truck, landing with his chin on the ground. He was neurologically intact and no loss of consciousness was reported. Staff from the oral and maxillofacial department were called to the emergency unit because the patient was unable to open his mouth. Physical examination revealed an extremely concave profile with a senile aspect of the face and bilateral preauricular skin depressions ( Fig. 1 ). On the intraoral aspect, neither the maxillary alveolar process nor the teeth could be seen. The patient had the aspect of a severe prognathism with an edentulous maxilla ( Fig. 2 ). Radiographic examinations, including lateral, postero-anterior, Watters and Townes views showed a bilateral anterior mandibular condyle dislocation and complete intrusion of the mandible over the maxilla; the anatomy of maxillary teeth was recognized at the level of the apex of mandibular teeth. The coronoid process was impacting with the body of the zygoma ( Fig. 3 ). No signs of mandibular or maxillary fractures were found. A successful close reduction of the TMJ was made under conscious sedation, without any complications. Once the mandible was disimpacted and the condyles were returned to their normal position, maxillary bone and teeth were observed, and adequate occlusion was obtained. The patient had clinical absence of bilateral first maxillary molars and a bilateral posterior cross bite ( Fig. 4 ). There were a few mucosal lacerations due to mandibular teeth indentations that did not need to be repaired. The patient’s facial aspect and profile changed from senile and extremely concave to a normal young aspect ( Fig. 5 ). A postreduction lateral radiograph showed a normal skeletal profile, with the mandibular condyles back in their normal position inside the glenoid fossa. The maxilla and mandible were both perfectly identified with no sign of bone fractures. The first maxillary molars and the right second premolar were seen impacted inside the maxillary bone; this impaction was present before the motor vehicle accident ( Fig. 6 ). The patient was oriented to control jaw movements and had a soft diet for 2 weeks. He has been followed up for 6 months with no further complications.