Residency · Residency · Oral Maxillofacial Surgery

Anatomy of the Temporomandibular Joint

Overview

The TMJ is a bilateral ginglymoarthrodial (hinge and sliding) synovial joint and the only joint in the body with a fibrocartilaginous articular surface rather than hyaline cartilage. Its complex biomechanics, involving both rotation and translation, allow for mouth opening, lateral excursion, and protrusion. A thorough understanding of TMJ anatomy is essential for managing internal derangement, ankylosis, condylar fractures, and for performing arthroscopic and open joint procedures.

Osseous Anatomy

Mandibular Condyle

The mandibular condyle has an ellipsoid shape, measuring approximately 20 mm mediolaterally and 8-10 mm anteroposteriorly. Its long axis is directed posteromedially, with the medial pole projecting further than the lateral pole. The articular surface consists of fibrocartilage covering the superior and anterior surfaces. Below the condyle, the condylar neck is a narrowed region that represents a common fracture site. The pterygoid fovea, a depression on the anterior surface of the condylar neck, serves as the attachment point for the superior head of the lateral pterygoid muscle.

Temporal Component (Glenoid/Mandibular Fossa)

The temporal component includes several key structures. The articular eminence is a convex bony prominence anterior to the fossa, composed of thick cortical bone designed to bear load. The glenoid (mandibular) fossa is a concave portion posterior to the eminence made of thin bone that is not load-bearing in the healthy joint. The postglenoid process is a small bony projection posterior to the fossa. The articular tubercle marks the peak of the articular eminence and represents the point over which the condyle must translate during opening. The height and steepness of the eminence influence joint biomechanics and predisposition to dislocation.

Articular Disc

Morphology

The articular disc is a biconcave fibrocartilaginous structure divided into three zones: the anterior band (thicker, approximately 2 mm), the intermediate zone (thinnest, approximately 1 mm), and the posterior band (thickest, approximately 3 mm). The intermediate zone is avascular and aneural, allowing it to bear load without generating pain signals. The disc is composed primarily of type I collagen with interspersed glycosaminoglycans.

Attachments

The disc is attached firmly to the medial and lateral poles of the condyle via the collateral (discal) ligaments. Anteriorly, it merges with the joint capsule and receives fibers from the superior head of the lateral pterygoid. Posteriorly, it is continuous with the bilaminar zone, also known as the retrodiscal tissue.

Bilaminar Zone (Retrodiscal Tissue)

The bilaminar zone has two distinct laminae. The superior retrodiscal lamina (superior stratum) is composed of elastic fibers and attaches to the tympanic plate and postglenoid process; it pulls the disc posteriorly during closing. The inferior retrodiscal lamina (inferior stratum) is collagenous and attaches to the posterior condylar neck. Between these laminae lies loose connective tissue containing a retrodiscal venous plexus, arterioles, and nerve endings from the auriculotemporal nerve.

The retrodiscal tissue is richly vascularized and innervated, and it is the source of pain in internal derangement when it becomes loaded in place of the displaced disc. Over time, adaptive tissue changes can allow retrodiscal tissue to undergo fibrous metaplasia and become fibrocartilage-like, forming a functional pseudodisc in chronic anterior disc displacement without reduction.

Disc Function

The disc distributes loads across the joint surfaces and divides the joint into superior and inferior compartments. It moves with the condyle during translation due to its collateral ligament attachments. In the normal closed-mouth position, the posterior band sits at or near the 12 o'clock position relative to the condyle.

Joint Compartments

Superior Compartment

The superior compartment lies between the articular eminence and glenoid fossa above and the superior surface of the disc below. Translational movement occurs in this compartment, and it is the compartment accessed during arthroscopy. Its volume is approximately 1.0-1.5 mL.

Inferior Compartment

The inferior compartment lies between the condylar head and the inferior surface of the disc. Rotational movement occurs here. Its volume is approximately 0.5-1.0 mL.

Joint Capsule and Synovial Membrane

The fibrous capsule encloses the joint and attaches to the articular eminence, the circumference of the glenoid fossa, and the condylar neck. It is lax laterally and medially but tight anteriorly and posteriorly. The synovial membrane lines the inner surface of the capsule but does not cover the articular surfaces or the disc. It produces synovial fluid containing lubricin (for boundary lubrication) and hyaluronic acid (for viscous lubrication), which provides both lubrication and nutrition to the avascular articular surfaces.

Ligaments

Temporomandibular (Lateral) Ligament

The temporomandibular ligament is the primary ligament of the TMJ and the strongest and most clinically significant. It has an outer oblique portion and an inner horizontal portion, running from the zygomatic arch and articular tubercle to the lateral condylar neck. Its function is to limit posterior and inferior displacement of the condyle and restrict retrusion.

Sphenomandibular Ligament

The sphenomandibular ligament is an accessory ligament extending from the spine of the sphenoid to the lingula of the mandible. It is a remnant of Meckel cartilage. It becomes taut during wide opening and may act as a fulcrum (swing axis).

Stylomandibular Ligament

The stylomandibular ligament is another accessory ligament, running from the styloid process to the posterior border and angle of the mandible. It limits excessive protrusion and separates the parotid from the submandibular gland.

Muscles of Mastication

Masseter

The masseter originates from the zygomatic arch (the superficial head from the anterior two-thirds, the deep head from the posterior one-third and medial surface) and inserts on the lateral surface of the mandibular ramus and angle. It is the most powerful elevator of the mandible and is innervated by the masseteric nerve from the anterior trunk of V3.

Temporalis

The temporalis originates from the temporal fossa and temporal fascia and inserts on the coronoid process and anterior border of the ramus. Its vertical fibers produce elevation while its posterior fibers produce retrusion. It is innervated by the deep temporal nerves from the anterior trunk of V3.

Medial Pterygoid

The medial pterygoid has a deep head originating from the medial surface of the lateral pterygoid plate and a superficial head from the tuberosity of the maxilla. It inserts on the medial surface of the mandibular angle and ramus at the pterygoid tuberosity. It produces elevation, protrusion, and contralateral excursion. It is innervated by the nerve to the medial pterygoid from the main trunk of V3.

Lateral Pterygoid

The lateral pterygoid has two heads. The superior head originates from the greater wing of the sphenoid and inserts into the anterior disc margin and the pterygoid fovea of the condyle. The inferior head originates from the lateral surface of the lateral pterygoid plate and inserts into the pterygoid fovea of the condylar neck. The inferior head produces protrusion when acting bilaterally, contralateral excursion when acting unilaterally, and depression when working with the suprahyoid muscles. The superior head stabilizes the disc during closing through eccentric contraction. Both heads are innervated by the nerve to the lateral pterygoid from the anterior trunk of V3. The lateral pterygoid is the only muscle of mastication that depresses the mandible.

Suprahyoid Muscles (Accessory Depressors)

The suprahyoid muscles, including the digastric (anterior belly innervated by the mylohyoid nerve, posterior belly by CN VII), mylohyoid, and geniohyoid, depress the mandible when the hyoid is fixed by the infrahyoid muscles.

Neurovascular Supply

Innervation

The primary sensory nerve of the TMJ is the auriculotemporal nerve, from the posterior trunk of V3, which encircles the middle meningeal artery with two roots. The masseteric nerve and deep temporal nerves provide accessory sensory innervation to the anterior joint capsule. Proprioceptive fibers from the joint capsule and retrodiscal tissue relay information to the mesencephalic nucleus of the trigeminal nerve.

Vascular Supply

The superficial temporal artery supplies the lateral capsule and retrodiscal tissue. The maxillary artery, specifically through its middle meningeal and deep auricular branches, supplies the deep structures. The anterior tympanic artery supplies the posterior capsule. The retrodiscal tissue contains a rich vascular plexus that fills and empties with jaw movement, functioning as a hydraulic cushion.

TMJ Biomechanics

Mouth Opening

Mouth opening occurs in two phases. Phase 1 (initial opening, 0-25 mm) involves rotation of the condyle within the inferior compartment as a hinge axis movement. Phase 2 (continued opening, 25-50+ mm) involves translation of the condyle-disc complex along the articular eminence in the superior compartment. Normal maximum opening ranges from 40 to 55 mm of interincisal distance. Normal lateral excursion is 8-12 mm, and normal protrusion is 8-10 mm.

Centric Relation

In centric relation, the condyle is seated in its most superior and anterior position within the glenoid fossa, resting against the posterior slope of the articular eminence with the disc interposed. This represents the musculoskeletally stable position of the condyle.

Loading

Joint loading occurs during clenching, grinding, and mastication. Loads are concentrated on the articular eminence and the lateral pole of the condyle, and the disc distributes these loads across a broader surface area.

Surgical Approaches to the TMJ

Preauricular Approach

The preauricular approach is the standard approach for open TMJ surgery, including discectomy, disc repositioning, and condylectomy. The incision is placed along the helical crus and extended inferiorly along the preauricular crease, with dissection through skin, subcutaneous tissue, and the temporal fascia (superficial layer). The key danger is the temporal branch of the facial nerve, which runs within or just deep to the superficial temporal fascia (temporoparietal fascia); staying deep to the superficial layer of the deep temporal fascia protects it. The endaural modification places the incision along the tragal margin for improved cosmesis.

Arthroscopic Portals

The posterolateral portal is the standard entry point, positioned along a canthal-tragal line approximately 10 mm anterior to the tragus and 2 mm below the line. The anterolateral portal is used for instrumentation during operative arthroscopy. Entry is into the superior joint compartment, and the auriculotemporal nerve and superficial temporal vessels are at risk.

Retromandibular (Risdon) Approach

The retromandibular approach provides access to the condylar neck and subcondylar region. The incision is made 3-5 cm below the mandibular angle, through skin, platysma, and the parotid capsule. The marginal mandibular branch of the facial nerve and the retromandibular vein are at risk.

Submandibular Approach (for Low Condylar Fractures)

The submandibular approach can access the subcondylar region but carries risk to the marginal mandibular nerve.

<image>Sagittal section through the temporomandibular joint in the closed-mouth position showing the mandibular condyle seated in the glenoid fossa with the articular disc interposed. The disc is labeled with its anterior band, intermediate zone, and posterior band. The bilaminar zone (retrodiscal tissue) is shown posteriorly with its superior and inferior laminae and the retrodiscal venous plexus. The superior and inferior joint compartments are labeled. The articular eminence is shown anteriorly. The lateral pterygoid muscle (superior and inferior heads) attaches to the anterior disc and condylar neck.</image>

<image>Lateral view of the TMJ and surrounding muscles of mastication. The masseter, temporalis, medial pterygoid, and lateral pterygoid muscles are shown in their anatomical positions relative to the mandibular ramus and condyle. The zygomatic arch is cut away to reveal the deep structures. Force vectors for each muscle are indicated with arrows showing the direction of mandibular movement they produce.</image>

<image>Sagittal MRI-style illustration comparing normal disc position (posterior band at 12 o'clock over the condyle in closed-mouth position) with anterior disc displacement with reduction (disc displaced anteriorly in closed position, reducing to normal position upon opening) and anterior disc displacement without reduction (disc remains anterior in both closed and open positions). The condyle, disc, and articular eminence are labeled in each panel.</image>

Clinical Pearls

The disc is avascular and aneural in its load-bearing intermediate zone, which means pain in internal derangement arises from the richly innervated retrodiscal tissue being loaded when the disc is displaced. The bilaminar zone can undergo fibrous metaplasia to form a functional pseudodisc in chronic disc displacement without reduction, which explains why many patients become pain-free even after disc displacement. The temporal branch of the facial nerve is the structure most at risk during preauricular TMJ approaches, and staying deep to the superficial layer of the deep temporal fascia protects it. Maximum opening below 35 mm is clinically significant and warrants investigation. The lateral TMJ ligament is the primary restraint against posterior condylar displacement, and its disruption contributes to joint instability. The superior head of the lateral pterygoid attaches to the disc and plays a key role in disc stabilization; its dysfunction may contribute to internal derangement. Crepitus indicates degenerative joint disease with bone-on-bone articulation, while clicking suggests disc displacement with reduction. Arthroscopic access is to the superior joint compartment; the inferior compartment is not routinely accessed arthroscopically.

References

• Okeson JP. Management of Temporomandibular Disorders and Occlusion. 8th ed. Mosby; 2019.
• Miloro M, Ghali GE, Larsen PE, Waite PD. Peterson's Principles of Oral and Maxillofacial Surgery. 3rd ed. People's Medical Publishing House; 2012.
• Hylander WL. Functional anatomy and biomechanics of the masticatory apparatus. In: Laskin DM, et al., eds. Temporomandibular Disorders: An Evidence-Based Approach to Diagnosis and Treatment. Quintessence; 2006.
• Wilkes CH. Internal derangements of the temporomandibular joint. Pathological variations. Arch Otolaryngol Head Neck Surg. 1989;115(4):469-477.
• McCain JP, de la Rua H. Principles and practice of operative arthroscopy of the human temporomandibular joint. Oral Maxillofac Surg Clin North Am. 1989;1:135-151.

Read this lecture as Markdown