Where is the articular tubercle located?
The articular tubercle is part of the squamous part (pars squamosa) of the temporal bone. Topographically, it is defined by the following landmarks:
- Zygomatic process (processus zygomaticus) — the tubercle is located at its base. The process itself participates in the formation of the zygomatic arch.
- Mandibular fossa (fossa mandibularis) — the tubercle lies anterior to it. The mandibular fossa has an articular surface (facies articularis) bounded by the articular tubercle.
Structure and cartilage covering
Anatomically, the articular tubercle is a cylindrical eminence 5 to 25 mm in height. Its structure features two slopes that serve as the functional (working) parts of the joint:
- Anterior slope — located anterior to the apex of the tubercle.
- Posterior slope — located anterior to the mandibular fossa.
Cartilage features: The entire articular tubercle is covered with fibrous articular cartilage. The cartilage of the bony articular surfaces is connective-tissue-based rather than hyaline; it is thin and fragile.
Role in TMJ biomechanics
The articular tubercle of the temporal bone, along with the mandibular fossa and the condylar process of the mandible, constitutes the articular surfaces of the temporomandibular joint.
- Compensation of incongruency: There is a size mismatch between the mandibular head and the mandibular fossa, causing instability in the intra-articular relations. This incongruency is eliminated by the biconcave articular disc (discus articularis).
- Division of movements: The articular disc divides the TMJ cavity into two compartments. Rotational movements occur in the inferior compartment, while translational movements (gliding) occur in the superior compartment.
- Joint stabilization: Joint stability depends entirely on occlusion (dental alignment) and the tone/state of the masticatory muscles.
Clinical significance and pathologies
The articular tubercle is involved in the pathogenesis of TMJ disorders:
- TMJ dislocations: Upon mouth opening, the condylar process may displace excessively anteriorly, moving past the articular tubercle. In chronic dislocation of the mandibular head, the head returns posteriorly on its own, whereas recurrent dislocation requires targeted manual reduction.
- Secondary osteoarthritis: Develops in late stages of TMJ locking — more than 6 months. It is characterized by deformation of bony structures, defects in the cartilage covering, and the formation of osteophytes. The deformed articular disc may fuse with the posterior slope of the articular tubercle.
- Reactive synovitis: May accompany any clinical form of internal TMJ derangement and occurs as a result of chronic microtrauma to joint tissues and strain on intra-articular ligaments.
Class and exam questions
What type of cartilage covers the articular tubercle?
It is covered with fibrous connective-tissue cartilage. This cartilage is not hyaline; it is thin and fragile.
What anatomical parts of the articular tubercle are distinguished?
The tubercle has the shape of a cylindrical eminence 5 to 25 mm in height with two slopes: the anterior slope, located anterior to the apex, and the posterior slope, located anterior to the mandibular fossa. Both slopes serve as the working parts of the joint.
What happens to the articular tubercle during mandibular dislocation?
In chronic dislocation of the mandibular head, the condylar process displaces excessively anteriorly and moves beyond the articular tubercle. When the head shifts toward the anterior slope of the articular tubercle, a click occurs, which repeats upon mouth closing.
How does the articular tubercle change in secondary TMJ osteoarthritis?
In secondary osteoarthritis, deformation of bony structures, defects in the cartilage covering, and the formation of osteophytes occur. Fusion of the deformed articular disc with the posterior slope of the articular tubercle is also possible.
What else to study on this topic
- Mandibular fossa of the temporal bone
- Articular disc of the temporomandibular joint
- Head of the mandible (condylar process)
- Temporomandibular joint (TMJ)
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