What is the role of the articular disc in the temporomandibular joint (TMJ) and how is it related to TMJ disorders, particularly in adult women?

Articular Disc Anatomy and Role in TMJ Function

Structural Anatomy of the Articular Disc

The articular disc is a fibrocartilaginous structure that divides the temporomandibular joint into upper and lower compartments, serving as the critical interface between the mandibular condyle and temporal bone. 1, 2

Posterior Attachment (Retrodiscal Tissue)

• The posterior attachment consists of two distinct layers with different biomechanical properties 1
• Upper layer (bilaminar zone): Contains elastic fibers, collagen fibers, fat deposits, and blood vessels; attaches posteriorly to the post-glenoid tubercle, tympanic wall of temporal bone, cartilaginous meatus, and parotid gland lining 1
• Lower layer: Consists of compact, non-elastic collagen fibers attached to the posterior surface of the condyle 1
• The elastic fibers in the upper layer play a crucial role in repositioning the disc during jaw closure, acting as a recoil mechanism 1

Lateral and Medial Attachments

• Lateral attachment: The disc attaches to the fascia of the masseter muscle and the lateral ligament, which inserts into the temporalis fascia 3
• Medial attachment: The disc and its capsular attachments are in close contact with the fascia of the lateral pterygoid muscle 3
• A small portion of the upper head of the lateral pterygoid muscle inserts directly into the anteromedial part of the articular disc, allowing direct muscular influence on disc position 3

Capsular Relationships

• True capsular elements directly connecting temporal bone to mandible exist only on the lateral side of the joint 3
• In posterior, anterior, and medial regions, the upper and lower laminae of the disc attach separately to either temporal bone or mandibular condyle 3
• The capsular texture and articular cavity shaping permit disc movements predominantly in the anteromedial direction 3

Functional Role of the Articular Disc

Biomechanical Functions

• The disc acts as a biomechanical restrictor that guides and conditions TMJ movements during opening, closing, protrusion, and lateral jaw movements 4
• It distributes loading forces between the condyle and temporal bone during mastication 4
• The disc maintains proper spatial relationships between joint components throughout the range of motion 4

Muscular Control of Disc Position

• Both upper and lower heads of the lateral pterygoid muscle directly influence disc position during TMJ movements 3
• The temporalis and masseter muscles do not act directly on the disc but signal disc position via muscle spindle afferents 3
• This neuromuscular feedback mechanism helps coordinate disc-condyle relationships during function 3

Relationship to TMJ Disorders in Adult Women

Prevalence and Demographics

• TMD affects 5-12% of the population with peak incidence at 20-40 years of age and is more common in females 5
• Only 5% of TMD cases represent true intra-articular pathology involving the disc, while 85-90% are muscular in origin 6, 5, 7

Disc-Related Pathology (Internal Derangement)

• Internal derangement involves displacement of the articular disc, occurring with or without reduction 5, 8
• Disc displacement is among the most frequently found TMJ disorders and can occur in anterior, lateral, or medial directions 5
• When the disc is displaced, mechanical symptoms develop including clicking, locking, catching, and limited range of motion 8

Clinical Significance in Reconstruction

• Preservation and reattachment of the TMJ disc and lateral pterygoid muscle within the glenoid fossa sustains normal TMJ functionality and diminishes the likelihood of re-ankylosis following reconstruction 6
• When the articular disc is absent during reconstruction procedures, temporalis muscle and fascia flaps serve as interpositional materials 6
• The presence or absence of an intact articular disc significantly impacts surgical outcomes, with disc preservation associated with better long-term function 6

Diagnostic Considerations

• MRI is the gold standard for evaluating disc position and ligamentous structures 5
• CT/CBCT is appropriate for bone assessment but not for disc evaluation 5
• Radiological examination is indicated only when clinical examination provides insufficient information 5

Critical Clinical Pitfall

The most important clinical distinction is recognizing that only 5% of TMD cases involve true disc pathology requiring invasive intervention, while 85-90% are muscular disorders treatable with conservative management 6, 7. Approximately 50% of patients presenting with TMJ-region symptoms have complications unrelated to the TMJ itself, emphasizing the critical importance of accurate differential diagnosis before attributing symptoms to disc pathology 5, 7.