Temporomandibular joint

Last revised by Rohit Sharma on 5 Nov 2023

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).

  • location: between mandibular condyle and mandibular fossa of squamous temporal bone

  • movement

    • superior discotemporal compartment: protraction, retraction and gliding side-to-side (translation movements)

    • inferior discomandibular compartment: opening and closing (rotation)

  • ligaments and tendons: temporomandibular, stylomandibular and sphenomandibular ligaments

  • innervation

Being a synovial joint, it is surrounded by an outer fibrous capsule and inner synovial membrane. The fibrous capsule is attached inferiorly to the head of the condyle immediately 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.

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

  • lower compartment: opening and closing

  • major (intrinsic) ligament: temporomandibular ligament

    • thickened lateral portion of the capsule

    • strengthens the TMJ laterally

  • minor (extrinsic) ligaments: stylomandibular and sphenomandibular ligaments

The articular disc is comprised of fibrocartilage and has a biconcave shape with a thin center and thickened periphery. The thickened anterior and posterior parts are called the anterior (A) and posterior (P) bands respectively. The thinner central part is the intermediate zone (IZ).

The peripheral parts of the disc is attached to the joint capsule, except posteriorly where the posterior band blends with the retrodiscal (bilaminar) zone.

The disc divides the TMJ into a superior discotemporal space which allows anterior translation and inferior discomandibular space which allows rotation during mouth opening.

In the closed mouth position, the mandibular condyle is centered within the mandibular fossa. In the open mouth position, the condyle moves anteriorly under the center of the articular eminence.

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.

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 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. 

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