Temporomandibular joint

The temporomandibular joint (TMJ) is an atypical synovial joint located between the condylar process of the mandible and the mandibular fossa and articular eminence of the temporal bone. It is divided into a superior discotemporal space and inferior discomandibular space by the TMJ disc (or meniscus).

Summary

• location: between mandible and mandibular fossa of squamous temporal bone
• movement
  • upper compartment: protraction, retraction and gliding side-to-side
  • lower compartment: opening and closing
• ligaments and tendons: temporomandibular, stylomandibular and sphenomandibular ligaments
• innervation
  • auriculotemporal nerve
  • masseteric nerve

Gross anatomy

The joint is surrounded by a capsule which is attached inferiorly to the head of the condyle (above the pterygoid fovea - attachment of the inferior belly of the lateral pterygoid muscle) and superiorly to the margins of the mandibular fossa (posteriorly) and articular eminence (anteriorly) of the temporal bone.

Location

• located between the condylar process of the mandible and the mandibular fossa and articular eminence of the temporal bone

Movement

• upper compartment: protraction, retraction and gliding side-to-side
• lower compartment: opening and closing

Ligaments

• major ligament: temporomandibular ligament
  • thickened lateral portion of the capsule
  • strengthens the TMJ laterally
• minor ligaments: stylomandibular and sphenomandibular ligaments

Articular disc

Between the posterior band of the TMJ disc and the capsule is the retrodiscal zone (or bilaminar zone).

Normally in the closed mouth position, the disc lies above the condyle, with the junction of the posterior band and interlaminar zone within 10° of vertical. Using this measurement, however, up to 33% of asymptomatic individuals have displaced discs. Thus some authors suggest using 30° as the cut-off to improve specificity ¹. 

The mandibular condyle is centered on the mandibular fossa (also known as the glenoid fossa) when the mouth is closed. When the mouth is open, the condyle moves anteriorly under the center of the articular eminence.

The disc has anterior (A) and posterior (P) bands. The thinner central portion is called the intermediate zone (IZ). The posterior band is normally located directly on top of the condyle (C) when the mouth is closed. The intermediate zone should be between the condyle and the closest portion of the temporal bone in any mouth position.

The posterior aspect of the disc attaches to the bilaminar zone, collagen fibers that pull the disc back when it moves forward.

Blood supply

• branches of the external carotid artery, primarily superficial temporal artery

Innervation

• sensory innervation is from small articular branches of two nerves:
  • auriculotemporal nerve
  • masseteric nerve

Radiographic features

MRI

The disc has a low signal on all MRI sequences, but it may be possible to see intermediate signal centrally in the anterior and posterior bands. 

Related pathology

• TMJ dislocation
• TMJ dysfunction
• TMJ trauma
• TMJ effusion
• TMJ inflammation
• TMJ osteoarthritis