Case report

A 30-year-old Brazilian male, a victim of a trauma to the chin, was attended with preauricular swelling and limited mandible movement. Physical examination revealed facial asymmetry with chin deviation to the left, anterior open bite of approximately 7 mm, inability to close into occlusion and lack of mandibular excursion ( Fig. 1 ). No oral or facial lacerations were noted. Pain and preauricular depression were found during palpation.

Clinical aspect of posterior dislocation of the condyle.

A panoramic radiograph revealed no mandible fractures but the condyle appeared posteriorly displaced ( Fig. 2 ). No computed tomography (CT) image was available. The otolaryngology service was consulted and examination of the external auditory meatus showed an intact tympanic membrane with no evidence of fracture of the tympanic plate, cerebrospinal fluid, otorrhea or hemorrhage.

Panoramic radiograph showing posterior condyle positioned on the left side.

Treatment consisted of closed reduction of the condyle under general anesthesia, using percutaneous traction with a zygomatic hook placed in the mandibular notch. Bleeding through the external auditory canal was observed after reduction, but no external auditory canal stenosis or other otologic complications occurred postoperatively ( Fig. 3 ).

(A) Zygomatic hook placed in the mandibular notch and (B) bleeding through the external auditory canal right after reduction.

The patient was oriented to control jaw movements, and was given non-steroidal anti-inflammatory drugs and a restricted diet for 14 days. A postoperative panoramic radiograph showed that the mandibular condyle had been restored to its correct position within the glenoid fossa and symmetrical border of the mandible ( Fig. 4 ).

Clinical aspect of the postoperative procedure.

Discussion

Trauma to the mandibular midline with enough force to cause injury to the TMJ usually produces a subcondylar fracture. Traumatic posterior dislocation of the intact condyle is rare .

Complete dislocation of the mandibular condyle from the glenoid fossa can be classified as: anterior, posterior, lateral or superior. Traumatic dislocation is more common in the middle cranial fossa with approximately 49 reports from 1960 to 2007 . In the literature, 12 articles describe superior–lateral dislocation . Only one case of posterior dislocation without fracture has been reported in the English literature .

Condylar dislocation may be related to the force and direction of the trauma, and depend on whether the mouth is open or if there is a lack of posterior occlusion, abnormalities of condylar morphology, or a particularly thin roof of the glenoid fossa .

S eymour and M usgrove suggested that the combination of an open-mouth position on impact with a posterior–superiorly directed blow to the chin may produce a dislocation of the condyle into the middle cranial fossa. F onseca found that the condylar head is larger than the glenoid fossa, making central luxation difficult. Younger individuals can have underdeveloped medial and lateral poles of the mandibular condyle, and a rounded condyle may be more easily superiorly displaced through the relatively weak middle of the glenoid fossa into the middle cranial fossa .

Regarding posterior dislocation, some anatomic features should be considered. In a horizontal section through the skull, just below the posterior articular ridge there is a triangular area devoid of bone. The lateral half of the condyle is not supported by bone posteriorly. A small area in the posterior medial aspect of the glenoid fossa has no bony support. Soft tissue examination shows that the superficial 8 mm of the external auditory canal is incompletely surrounded by cartilage .

If the condyle is forced against the tympanic plate of the temporal bone rather than that portion of the canal unsupported by bone, fracture may occur. This anatomic gap associated with midline trauma with posterior vector causes condylar dislocation with or without concomitant condylar fracture .

A kers et al stated that in an edentulous patient the mandible could be in an overclosed position and when held in this position during a posterior force to the anterior portion of the mandible, the condyle can be displaced to the area of the external ear canal, where minimal posterior support exists. In the present case, the patient had complete dentition and the nature and direction of the trauma seems to explain the posterior displacement of the condyle.

Numerous treatments have been used for dislocation of the mandible. They include injection of sclerosing solutions, physical therapy, eminectomies, joint plication, pterygoid and temporalis myotomies, condylectomies and articular implants .

A review of the literature did not reveal many reports of posterior dislocation into the external auditory canal, which makes it difficult to determine a treatment protocol. Treatment of posterior dislocation of the mandible should be directed at: repositioning the condyle in the glenoid fossa; observing the involvement of the auditory apparatus (tympanic plate or external ear canal) and proximity to vital structures; maintaining the patency of the external auditory canal; and preventing TMJ ankylosis and infection.

Manual reduction is the first choice for condyle dislocation. A kers et al , in the only report of intact posterior condyle dislocation, used manual reduction under local anesthesia to move the condyle anteriorly into the glenoid fossa. In the present case, the conventional procedure was unsuccessful and surgery was used to obtain reduction. Posterior dislocation should be corrected immediately or with a few days. Postponing the procedure may result in fibrous tissue formation on the glenoid fossa, resulting in imperfect reduction. Inadequate reduction induces fibro-osseous ankylosis of the joint, which necessitates condylectomy with or without arthroplasty . Diet control, anti- inflammatory medication and mouth-opening training are recommended after reduction.

Complications associated with the surgical treatment include temporary auditory deficit associated with trauma to the tympanic membrane and the external ear canal. Maintaining the patency of the auditory canal and preventing infection minimize the risk of otologic damage .

In conclusion, posterior dislocation of the intact mandibular condyle is rare. Clinical features may mimic subcondylar fracture or superior dislocation of the mandible. Adequate imaging is required to diagnosis these injuries accurately. Conventional radiography shows the dislocation but it is not clear. CT should always be performed to assess the relationship of the condyle to other structures. Closed reduction is the first choice of treatment. Early intervention reduces the risk of fibrosis in the glenoid fossa or fibro-osseous ankylosis of the joint. Otologic examination is necessary to diagnose trauma to the external ear canal and tympanic membrane.