Dislocation of the temporomandibular joint can occur in the setting of trauma or during a wide opening of the mouth (eg. yawning, or during various medical procedures, such as transesophageal echocardiography). Inability to close the mouth is the main sign. The diagnosis, although often made solely on clinical criteria after a thorough physical examination, often requires the use of imaging studies, the most valuable being magnetic resonance imaging (MRI).
An array of conditions and risk factors have been described as potential causes of temporomandibular joint (TMJ) dislocation, which may be partial (subluxation) or complete (luxation) [1] [2] [3]. Trauma, epilepsy, laxity of the articular disc and weak supporting structures (muscles, ligaments, or tendons, seen in the elderly population who suffer from degenerative osteoarthritic changes), but also laughing, yawning, and attempting a large bite have all been documented as potential inducers of TMJ dislocation [1] [4] [5]. Furthermore, various medical and dental procedures (eg. transesophageal ultrasonography, extubation, endoscopy, etc.) that require profound and forced mouth opening are also documented as events that led to dislocation [4] [6] [7]. Regardless of the subtype (anterior, posterior, superior, medial, or lateral), spasm of the masseter, temporalis and pterygoid muscles ensues and prevents the mandibular condyle from attaching into the glenoid fossa [2]. Thus, the inability of patients to close their mouth is the hallmark of TMJ dislocation, whereas deviation of the chin to the opposite side of the fracture is often seen in unilateral fractures [1]. As the oral cavity remains open, patients experience drooling, inability to speak properly, and many report pain in the preauricular region (the pain is pronounced when patients attempt to close their mouth), in the proximity of the dislocated TMJ [1]. Several complications may arise, including injury to the external auditory canal (posterior and superior dislocations), damage of the facial (VII) and vestibulocochlear nerves (VIII) that can result in deafness, as well as cerebrospinal fluid (CSF) leakage (superior) [2].
Early recognition of the condition allows the physician to perform manual reduction without the use of anesthesia, thus a prompt diagnosis should be made [5]. Temporomandibular joint dislocation mandates a thorough clinical assessment, starting with a detailed patient history that will determine the event which led to the dislocation and observation of typical symptoms [1] [2]. During the physical examination, a vacant space in the preauricular area (the location of the joint) strongly suggests TMJ dislocation, as does chin deviation [1]. Although clinical criteria are considered sufficient for the diagnosis [4], imaging studies are the cornerstone in assessing the exact subtype of injury. Plain radiography and computed tomography (CT) are useful in showing the displacement of the condylar head and the assessment of bony structures, and the three-dimensional (3D) CT scan is often recommended for its benefit of providing a complete view of the temporomandibular joint [1] [5] [8]. Due to its superior role in differentiating between soft tissue injuries, however, magnetic resonance imaging (MRI), is necessary in order to define the exact type of fracture and thus aid in optimizing the therapeutic approach [1] [5] [8] [9].