Clinical History
A healthy volunteer underwent MR examiation of his right TMJ.
Imaging Findings
The patient had not history of temporomandibular joint (TMJ) pathology and was completely asymptomatic. He underwent magnetic resonance (MR) examination of his right TMJ voluntarily.
Discussion
The TMJ is a diarthroidal joint located between the condyle of the mandible and the mandibular fossa and the articular eminence of the temporal bone. The mandibular condyle is elliptic shaped and its
transverse diameter is longer than sagittal one. The mandibular fossa (or articualr fossa) of the temporal bone is concave and is delimeted anteriorly by the convexity of the articular eminence. A
thin layer of hyaline cartilage covers the articulating cortical bone. An interposed fibrocartilaginous disc, or meniscus, divides the joint space into two not communicating parts: a large superior
space (disc-temporal space) and a little inferior space (disc-mandibolar space). This biconcave disc is composed of three parts: a thick anterior band, a thin intermediate zone, and a thick posterior
band. Small perforations in the intermediate portion of the disc are normal even if uncommon. The anterior band is anchored to the articular capsule and to the superior head of the lateral pterygoid
muscle. The posterior band blends with the bilaminar zone, consisting of highly vascularized, loose connective tissue. The bilaminar zone is composed of two ligaments: the posterior-superior
ligament, that inserts into the temporal bone, and the posterior-inferior ligament, that has insertion into the posterior subcondylar area. Lesions of these ligaments facilitate disc displacement.
Medially and laterally the disc is firmly attached to the capsule. In the closed-mouth position, the posterior band occupies a 12 o’clock position (+/- 10°) with respect to the mandibular
condyle, while the thin intermediate region is located betrween the temporal articular eminence and the anterior aspect of the condilar head, finally the anterior band is located under the articular
eminence and anterior to the condylar head. Opening the mouth, at first the mandibular condyle rotates forward under the disc, then the condylar head and the disc slide anteriorly below the articular
eminance. Therefore, in open-mouth position the central region of the disc is located between the condylar head and the articular eminance, while the posterior band is seen dorsal to the 12
o’clock position. In a normal joint, the medial and lateral edges of the disc do not bulges in relation to the mandibula condyle borders. The joint capsule is composed of loose connective
tissue and stretches from the edge of the mandibular fossa and the articular eminence of the temporal bone to the neck of the mandibular condyle. Three ligaments contribute to stability of this
joint: (1) laterally the temporomandibular ligament, which bridges the posterior zygomatic arch and the lateral aspect of the condilar neck, reinforces laterally the joint capsule; (2) medially the
sphenomandibular ligament, that inserts into the sphenoidal spine of the temporal bone and into the medial aspect of the mandibular branch; (3) posteriorly the stylomandibular ligament, which bridges
the sphenoid process and the posterior margin of the mandibular branch. The muscles of mastication are responsible of the movemnet of the jaw. Mouth closure is allowed by medial pterygoid, temporal
and masseter muscles, while mouth opening is effected by lateral pterygoid and suprahyoid muscles.
Differential Diagnosis List
Normal anatomy of the temporomandibular joint.
Final Diagnosis
Normal anatomy of the temporomandibular joint.
