Sandbox

Dislocation Type	Frequency	Mechanism	Additional Comments	Associated with fracture	Image
Anterior	Most common	Often occurs spontaneously while patient is yawning, "popping" ears, or laughing
Posterior	Rare
Lateral	Rare
Superior	Rare

Background

Sagittal section of the articulation of the mandible.

Anterior Dislocation

• Mandibular condyle forced in front of the articular eminence
• Risk factors:
  • Prior dislocation
  • Weakness or laxity of capsule
  • Ligamentous injury

Posterior Dislocation

• Follows a blow to the mandible that may or may not break the condylar neck
• Condylar head may prolapse into the external auditory canal

Lateral Dislocation

• Often associated with mandibular fracture

Superior Dislocation

• Occur from blow to the partially opened mouth
• Associated with cerebral contusions, facial nerve palsy, deafness

EX

while the other types are rare. Anterior dislocation shifts the lower jaw forward if the mouth excessively opens. This type of dislocation may happen bilaterally or unilaterally after yawning. The muscles that are affected during anterior jaw dislocation are the masseter and temporalis which pull up on the mandible and the lateral pterygoid which relaxes the mandibular condyle. The condyle can get locked in front of the articular eminence. Posterior dislocation is possible for people who get injured by being punched in the chin. This dislocation will push the jaw back affecting the alignment of the mandibular condyle and mastoid. The external auditory canal may be fractured. Superior dislocations occur after being punched below the mandibular ramus as the mouth remains half-open. Since great force occurs in a punch, the angle of the jaw will be forced upward moving towards the condylar head. This can result in a fracture of the glenoid fossa and displacement of the condyle into the middle cranial fossa, potentially injuring the facial and vestibulocochlear nerves and the temporal lobe. Lateral dislocations move the mandibular condyle away from the skull and are likely to happen together with jaw fractures.

Posterior, superior and lateral dislocations are uncommon injuries and usually result from high-energy trauma to the chin. By contrast, anterior dislocations are more often the result of low-energy trauma (e.g. tooth extraction) or secondary to a medical condition that affects the stability of the joint (e.g. seizures, ligamentous laxity, degeneration of joint capsule).