Chapter 161

Mandible or temporomandibular joint (TMJ) dislocations usually occur in the setting of prior musculoskeletal problems of the jaw.1–3 This includes joint laxity, prior injury or dislocation, inherent hypermobile syndromes (e.g., Marfan, Ehlers-Danlos), or neuromuscular problems (e.g., dystonic reactions) that pull the mandible out of its joint. The mandibular dislocation typically results from TMJ hyperextension or trauma. The Emergency Physician must be able to reduce a TMJ dislocation. The procedure is easy, simple, and straightforward.

The TMJ is an unusual joint (Figure 161-1). It is composed of two joints separated by an articular disk. The TMJ functions as a hinge and gliding joint. A discussion of the mechanics of the TMJ is beyond the scope of this chapter. Anterior dislocations are most commonly seen in the Emergency Department. The etiology of the dislocation includes laughing, chewing, opening the mouth wide (eating, for procedures, yawning, vomiting), seizures, and trauma. All of these actions can result in the mandibular condyle sliding forward and anterior to the articular eminence of the temporal bone. The muscular attachments of the mandible result in a pulling of the condyle superiorly and in front of the articular eminence (Figure 161-2). This causes the mandible to become fixed in dislocation and rarely spontaneously reduce.

###### Figure 161-1

Anatomy. A. Lateral view of the head and temporomandibular joint. B. Anatomy of the mandible. C. Sagittal section through the temporomandibular joint. D. The attachment of the muscles of mastication to the mandible. The arrows represent the direction of pull of the muscles.

###### Figure 161-2

Anatomic relationships of the mandible. A. The fully opened mandible. B. The anteriorly dislocated mandible.

TMJ dislocations are commonly anterior, but may be in any direction. Anterior TMJ dislocations may occur spontaneously in normal individuals and can occasionally reduce spontaneously. Dislocations of the TMJ are usually bilateral, but can occur unilaterally. Posterior, superior, and lateral dislocations are much more rare. They are seen in the context of direct trauma to the mandible, with or without an associated mandible fracture.

The diagnosis can often be made clinically in a cooperative patient with a nontraumatic history. The patient will present in pain with an open mouth, protruding mandible, and malocclusion. A unilateral dislocation will cause the mandible to protrude towards the non-dislocated side. A depression, palpable and visible, will be noted in the preauricular area. Mandibular radiographs are indicated when trauma is involved to rule out an associated fracture. The dislocation is often best seen on the Panorex view ...

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