TMJ is a synovial joint between the condyle of the mandible a mandibular fossa on the undersurface of the squamous part of the temporal bone.
The mandible is the single bone with the horizontal horseshoe-shaped body, which is continuous at its posterior ends with a pair of vertical rami, each ramus is surmounted by a head or condyle.
The temporomandibular joint allows opening and closing the mouth and complex chewing or side to side movements of the lower jaw.
The cranium with which the mandible articulates, is also mechanically, a single component, with a mandibular fossa on each side. This complex is ineffective functioning joint, as movement cannot take place at one temporomandibular joint, as movement cannot take place at one TMJ without a concomitant movement occurring at the joint on the opposite side.
The joint is separated into upper and lower joint cavities by a fibrocartilagenous disc within it. Both bone surfaces are covered with a layer of fibrocartilage identical with that of the disc. There is no hyaline cartilage in the joint, so it is an atypical synovial joint.
The capsule is attached high p on the neck of the mandible anteriorly, near the articular margin of the head, but lower down the neck posteriorly. Above, it is attached anteriorly just in front of the articular eminence of the temporal bone, posteriorly to the squamotympanic fissure, and medially and laterally to the margins of the mandibular fossa. It is lax above the disc, but taut below. The synovial membrane lines the inside of the capsule and the intracapsular posterior aspect of the neck of the mandible.
The articular disc attached around its periphery to the inside of the capsule and to the medial and lateral poles of the head of the mandible. Its upper surface is anteroposteriorly concavoconvex in the sagittal plane to fit the articular eminence and fossa. The inferior surface is concave in adaptation to the condyle. Anteriorly disc is continuous through its capsular attachment with the tendon of lateral pterygoid.
Posteriorly disc divided into two laminae. The upper fibroelastic lamina is attached to the margin of the mandibular fossa. The lower nonelastic fibrous lamina is attached to the neck of the mandible. Between the two laminae is a pad of loosely textured tissue continuing many blood vessels and sensory nerve endings. The disc has two transverse thickened bands it is thinnest and relatively avascular.
Temporal ligament and sphenomandibular ligament reinforce the capsule making it more strong.
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