TMJ disc | pacs

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The temporomandibular joint (TMJ) disc (or meniscus) is made of fibrocartilage and divides the joint into two compartments.

Gross anatomy

The disc is composed of fibrocartilage, with crimped collagen, thought to better absorb impacts. It has a biconcave shape with a thicker periphery attached at its periphery (except posteriorly) to the TMJ capsule (see below). Anteriorly and posteriorly transverse thickenings of the disc are known as the anterior and posterior bands. Between the two is the intermediate zone.

The TMJ disc divides the joint into two compartments and separates translational and rotational motion.

Above the disc, between it and the mandibular fossa and articular eminence of the temporal bone is the superior discotemporal space - anterior translation during mouth opening occurs here.

Below the disc, between it and the mandibular condyle, is the inferior discomandibular space - rotation occurs here (in absence of TMJ dysfunction).

Attachments

anterior: capsule which blends with the insertion of the superior belly lateral pterygoid muscle, and attaches to the articular eminence of the temporal bone superiorly and neck of condyle inferiorly
medial: capsule
lateral: capsule
posterior: blends with the retrodiscal layer

Radiographic features

MRI

The anterior band and intermediate zone are low signal on T2/PD sequences, whereas the posterior band and retrodiscal zone are intermediate to hyperintense. The intermediate zone may have a higher T2 signal cleft within it as a normal variant.

The anterior band is well seen on both open and closed mouth oblique sagittal views (see: TMJ MRI protocol), whereas the posterior band and retrodiscal zone are best seen in closed mouth views.

A normal disc is biconcave. In pathology this morphology alters, and the disc may appear