The mandible can be dislocated in an anterior, posterior, lateral, or superior plane. Anterior dislocation is most common and occurs when the mandibular condyle is forced in front of the articular eminence. The jaw is then kept in this position by muscular spasm. Anterior subluxation occurs in up to 70 percent of normal individuals but can be spontaneously reduced by the patient.12 A predisposition to symptomatic anterior dislocation includes anatomic predilection (a shallow glenoid fossa), loss of joint capsule integrity (previous trauma), or increased muscle tone. Once the jaw is dislocated, muscular spasm, particularly from the temporalis and lateral pterygoid muscles, tends to prevent reduction. Dislocations are most frequently bilateral, but they also occur unilaterally. 12
Anterior dislocations are classified as acute, chronic recurrent, or chronic.12 Acute dislocations usually present shortly after their occurrence, owing to severe discomfort. In chronic recurrent dislocations, precipitating factors should be considered. This includes dystonic reactions and hypermobile syndromes (e.g., Marfan, Ehlers-Danlos).12 Chronic dislocations, where the condyle is displaced from the fossa for an extended time, occur in patients unable or unwilling to obtain prompt medical treatment (e.g., severe mental illness, alcoholism, etc.).
Posterior dislocations are rare. They follow a direct blow to the chin that does not break the condylar neck. In this dislocation, the mandibular condyle is thrust against the mastoid. As a result, the condylar head may prolapse into the external auditory canal.12
Lateral dislocations are always associated with jaw fracture. With a lateral dislocation, the condylar head is forced laterally and then superiorly into the temporal space.
Superior dislocations occur from a blow to the partially open mouth that forces the condylar head upward. Associated injuries include cerebral contusions, facial nerve palsy, and deafness. Mandibular fractures are not always present.12 Clinical Features
Patients with acute dislocation usually present with severe pain, difficulty in speaking or swallowing, or malocclusion. There may be loose or missing teeth and areas of sensory deficit at the chin or mouth.
With anterior dislocation, pain is localized anterior to the tragus. The symptoms are frequently reported to have begun acutely following extreme mouth opening. Anterior dislocation has been reported to have occurred after laughing, yawning, vomiting, taking a large bite, trauma, oral sex, dental extraction, overstretching of the mouth during general anesthesia, or tonsillectomy.1 i2 As opposed to anterior dislocation, all other types of mandibular dislocation tend to require significant trauma.
All patients with a history of possible mandibular dislocation should have a good head, neck, and dental examination. With anterior dislocations, there is a visible and palpable preauricular depression from the displacement of the mandibular condyle. There will also be difficulty with jaw movement. If the dislocation is unilateral, there is deviation of the jaw away from the dislocation.
When a posterior dislocation is considered, the external auditory canal should be visualized. Baseline hearing function should be verified. With lateral dislocations, the condylar head is palpable in the temporal space and there are always signs of a jaw fracture (e.g., malocclusion). When a superior dislocation is suspected, a thorough exam is needed, especially focusing on the head, neck, and neurologic systems.
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