Unusual synovial joint where articular surfaces are covered with fibrocartilage, not hyaline cartilage.
Bones:
Temporal bone: Articular eminence anteriorly and posterior glenoid tubercle posteriorly, in between is the glenoid fossa
Mandible: Condylar head of the mandible articulates with glenoid fossa
Articular disc (meniscus):
Divides the joint into superior and inferior compartments
Biconcave fibrocartilage
Divides synovial joint into superior and inferior compartments
Round to oval in shape with a thin intermediate zone which separates thicker peripheral anterior and posterior bands
Anterior band:
Smaller than posterior band
Attached to joint capsule, condylar head, anterior margin of articular eminence, anteroinferior aspect of the condylar articular margin, superior belly of lateral pterygoid muscle
Intermediate zone:
Between anterior and posterior band
Posterior band:
Blends with bilaminar zone (areolar tissue, retrodiscal tissue, posterior ligament)
Bilaminar zone:
Synonyms: areolar tissue, retrodiscal tissue, posterior ligament
Rich neurovascular tissue
Attaches to mandibular condyle and temporal bone
MR disc anatomy:
Biconcave structure with homogeneous low signal intensity
Low signal on T1 and T2
Intermediate zone might show increased T2 signal
Attached posteriorly to bilaminar zone, which has intermediate signal
Posterior band and retrodiskal tissue are best seen on the open-mouth views
Anterior band and intermediate zone are of low signal and posterior band is slightly of high signal
Anterior band lies anterior to condyle
Movements:
1. Rotation around horizontal axis through condylar heads
2. Translation: condyle and meniscus move together anteriorly beneath articular eminence; In open mouth, the condyle lies beneath anterior band of the meniscus
Mouth opening is by lateral pterygoid muscle
Mouth closing is by medial pterygoid, temporalis and messeter
Closed-mouth:
Posterior band lies above condyle (12 o' clock)
Junction of posterior band and bilaminar within 10° of vertical (if the angle exceeds 10°, it may be pathological) (Figure: Radiographics link here)
Anterior disk displacement of up to 30° can be normal
Figures:
Normal anatomy: Link to Radiographics
References:
1. Resnick et al, Bone and joint imaging, 3rd edition, Elsevier Saunders publications
2. Tomas X et al. MR Imaging of Temporomandibular Joint Dysfunction: A Pictorial Review. RadioGraphics 2006;26:765-781
