Head and Neck Anatomy Series: Temporomandibular Joint (TMJ) Anatomy

Overview of TMJ

• Unique because it's a bilateral diarthrosis; both sides must function together.
• Performs both hinge and sliding movements (ginglymoarthrodial).
• Covered in fibrocartilage, not hyaline cartilage, withstands mastication forces.
• First joint to start developing around seven weeks in utero.
• Only joint with a rigid endpoint of closure at occlusal contact of teeth.

Articular Disc

• Made up of fibrocartilage, lacks blood vessels or nerve fibers, composed mostly of type 1 collagen.
• Bi-concave shape, thinnest in the center (intermediate zone), thickest at posterior band.
• Divides the joint into two compartments:
  • Upper joint space: Responsible for translational movements (protrusion/retrusion).
  • Lower joint space: Responsible for rotational movements (opening/closing mouth).
• Sometimes referred to as the meniscus.

Retrodiscal Tissues

• Superior Retrodiscal Lamina: Elastic fibers, attaches to the tympanic plate, prevents anterior dislocation.
• Inferior Retrodiscal Lamina: Collagen fibers (inelastic), attaches to condylar neck, prevents excessive rotation.
• Intermediate Retrodiscal Tissue: Loose connective tissue, vascular and innervated.

Synovial Membrane (Synovium)

• Specialized endothelial cells lining the joint capsule.
• Secretes synovial fluid for lubrication and nutrient distribution.

Bones of TMJ

• Condyle of the mandible, glenoid fossa of the temporal bone, articular tubercle of the temporal bone.
• Condyle can have several normal shapes; bilateral symmetry is important.
• Articular cartilage is strong, fibrocartilage (type 2 collagen), provides shock absorption.

Ligaments of the TMJ

• Connect bones, limit joint movement, made of type 1 collagen.

Intrinsic or Functional Ligaments

• Capsular Ligament: Encompasses joint space, retains synovial fluid, proprioceptive feedback.
• Lateral Ligament (Temporomandibular Ligament): Reinforces joint integrity, limits mouth opening and posterior dislocation.
• Collateral Ligaments (Discal Ligaments): Attach articular disc to condyle, divide joint into superior and inferior cavities.

Extrinsic or Accessory Ligaments

• Stylomandibular Ligament: Limits excessive protrusion of the mandible.
• Sphenomandibular Ligament: Supports mandible, embryonic remnant of Meckel's cartilage.
• Pterygomandibular Raphe: Connects buccinator and superior pharyngeal constrictor.
• Stylohyoid Ligament: Related to Eagle Syndrome, embryonic remnant of Reichert's cartilage.

Neurovascular Supply

• Mainly by the auriculotemporal nerve of the mandibular branch of the trigeminal nerve (V3).
• Vascular supply mainly by superficial temporal and maxillary arteries (branches of the external carotid artery).

Conclusion

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