Deep Face, TMJ, Infratemporal and Pterygopalatine Fossae

Articular surfaces:

• The mandibular condyle (head of the mandible) articulates with the articular tubercle and mandibular fossa of the temporal bone.
• It is a synovial joint, but atypical: both articulating bony surfaces are covered by fibrocartilage, rather than the hyaline cartilage typical of most synovial joints.
• This reflects the joint's unique developmental origin: intramembranous, rather than endochondral, ossification of the mandible.

Articular disc:

• A fibrocartilaginous disc divides the joint cavity into upper and lower compartments, each with its own synovial lining:
  • the upper compartment permits gliding/translation movement (disc + condyle moving together against the temporal bone)
  • the lower compartment permits rotation (condyle rotating against the disc)
• This combined joint (functionally a "hinge plus gliding" joint) is a compound synovial joint.
• The disc's mobility/integrity is central to normal, pain-free joint function (see Applied Anatomy for disc displacement).

Capsule:

• A loose fibrous capsule surrounding the joint, attached to the margins of the mandibular fossa/articular tubercle above and the mandibular neck below, permitting the joint's substantial range of movement.

Lateral ligament (temporomandibular ligament):

• A thickening of the lateral capsule, running from the zygomatic arch to the mandibular neck's posterolateral surface, the main structural reinforcement resisting posterior displacement of the condyle.

Accessory ligaments:

• Sphenomandibular ligament: from the spine of the sphenoid to the lingula of the mandible (not directly capsular, but providing additional suspensory support, and a useful surgical landmark near the mandibular foramen/inferior alveolar nerve entry point).
• Stylomandibular ligament: a thickened band of deep cervical fascia from the styloid process to the mandibular angle, separating the parotid and submandibular gland regions, of relatively minor direct joint-stabilising function but anatomically relevant as a regional landmark.

Movements:

• Depression (opening): Combined rotation (lower compartment, initial phase) and anterior translation/gliding (upper compartment, as the mouth opens further) of the condyle-disc complex.
• Elevation (closing): The reverse sequence.
• Protrusion/retrusion: Bilateral anterior/posterior gliding.
• Lateral excursion (side-to-side, e.g., grinding): One condyle rotates in place while the other translates anteriorly, this combined, bilaterally coordinated but asymmetric movement pattern underlies normal chewing/grinding function.

• All derived embryologically from the first pharyngeal arch, and therefore uniformly innervated by the mandibular division of the trigeminal nerve (CN V3): directly paralleling the facial expression muscles' shared second-arch/CN VII innervation pattern.

Masseter:

• Origin: Zygomatic arch.
• Insertion: Angle and ramus of the mandible (lateral surface).
• Innervation: Mandibular nerve (CN V3), masseteric branch.
• Action: Elevates the mandible (closes the jaw), the most powerful jaw-closing muscle, readily palpable when clenching the teeth.

Temporalis:

• Origin: Temporal fossa (broad fan-shaped origin).
• Insertion: Coronoid process and anterior ramus of the mandible.
• Innervation: Mandibular nerve (CN V3), deep temporal branches.
• Action: Elevates the mandible (anterior/vertical fibres); retracts the mandible (posterior, more horizontal fibres), a dual-action muscle given its broad fan-shaped fibre orientation.

Medial pterygoid:

• Origin: Medial surface of the lateral pterygoid plate (deep head) and the maxillary tuberosity/pyramidal process of the palatine bone (superficial head).
• Insertion: Medial surface of the mandibular angle/ramus, forming, together with masseter on the lateral surface, a muscular "sling" that supports the mandibular angle.
• Innervation: Mandibular nerve (CN V3), medial pterygoid branch.
• Action: Elevates the mandible; assists in protrusion and contributes to the grinding/lateral excursion movement.

Lateral pterygoid:

• Origin: Two heads, superior head, from the infratemporal surface/crest of the greater wing of sphenoid; inferior head, from the lateral surface of the lateral pterygoid plate.
• Insertion: Superior head, into the TMJ articular disc/capsule directly (a distinctive feature, unlike any other muscle of mastication); inferior head, into the pterygoid fovea on the mandibular condylar neck.
• Innervation: Mandibular nerve (CN V3), lateral pterygoid branch.
• Action: The primary protruder and depressor-initiator of the mandible. The inferior head pulls on the condylar neck and the superior head pulls on the disc, actively drawing the condyle-disc complex forward during jaw opening.
• Unilateral contraction produces contralateral lateral excursion (grinding movement).
• This is the muscle responsible for the jaw deviating toward the weak side in a CN V3 lesion: the unopposed contralateral lateral pterygoid pushes the jaw toward the paralysed side.

Boundaries:

• Roof: Infratemporal surface/crest of the greater wing of sphenoid (with a gap here, the foramen ovale/spinosum region, communicating with the middle cranial fossa).
• Medial wall: Lateral pterygoid plate (with the pterygomaxillary fissure, communicating with the pterygopalatine fossa).
• Lateral wall: Ramus of the mandible (with the mandibular notch above, and the condyle/coronoid process bounding it).
• Anterior wall: Posterior surface of the maxilla (with the inferior orbital fissure above, communicating with the orbit).
• Posterior: Open, continuous with the region below the TMJ/parotid region (no discrete bony posterior wall).
• Floor: Not a discrete bony floor, continuous inferiorly with the neck's soft tissue, near the medial pterygoid's insertion region.

Contents:

• Medial and lateral pterygoid muscles.
• Maxillary artery.
• Pterygoid venous plexus: an extensive venous network surrounding the pterygoid muscles, draining via the maxillary vein to the retromandibular vein.
• It has rich communications with the cavernous sinus via emissary veins through the foramen ovale/foramen lacerum region.
• This provides another potential pathway, alongside the danger triangle of the face, for infection to spread from the deep face into the cavernous sinus.
• Mandibular nerve (CN V3) and its branches.
• Chorda tympani (joins the lingual nerve within this fossa, having descended from the middle ear via the petrotympanic fissure).
• Otic ganglion.

Main trunk:

• Exits the skull via foramen ovale, immediately dividing (a short distance below the foramen) into a small anterior division (predominantly motor) and a larger posterior division (predominantly sensory), within the infratemporal fossa.

Anterior division:

• Gives rise to the motor branches to masseter, temporalis (deep temporal nerves), and the medial and lateral pterygoids, plus one sensory branch: the buccal nerve.
• The buccal nerve is sensory to the cheek mucosa/skin, NOT motor to buccinator, which is facial nerve-innervated. This is a commonly confused point, given the similar naming.

Posterior division:

• Gives rise to three major sensory branches (and the small motor nerve to mylohyoid, which travels alongside the inferior alveolar nerve despite the posterior division being predominantly sensory), auriculotemporal, lingual, and inferior alveolar nerves.

Auriculotemporal nerve:

• Typically arises as two roots that encircle the middle meningeal artery before reuniting (a notable anatomical relationship).
• It then passes posteriorly close to the TMJ and parotid gland, carrying the postganglionic parasympathetic secretomotor fibres to the parotid gland from the otic ganglion.
• It then ascends to supply sensation to the temporal scalp region and the external ear/tympanic membrane's outer surface.

Lingual nerve:

• Descends medial to the lateral pterygoid, then medial to the mandibular ramus, running anterior and slightly superior to the inferior alveolar nerve.
• It is joined by the chorda tympani (carrying taste and parasympathetic fibres) within the infratemporal fossa.
• It then continues forward to supply general sensation to the anterior two-thirds of the tongue and the floor of the mouth.
• Its close relationship to the submandibular duct becomes relevant more anteriorly, in the floor of mouth region.

Inferior alveolar nerve:

• Descends between the sphenomandibular ligament and the ramus of the mandible, entering the mandibular foramen (on the medial surface of the ramus, a key landmark for the inferior alveolar nerve block, see Applied Anatomy).
• It runs within the mandibular canal, supplying the lower teeth via dental branches, before exiting via the mental foramen (as the mental nerve, supplying the chin/lower lip skin).
• It also gives off the small motor nerve to mylohyoid just before entering the mandibular foramen, supplying mylohyoid and the anterior belly of digastric.

• The larger terminal branch of the external carotid artery, arising within the parotid gland, then passing into the infratemporal fossa (either superficial or deep to the lateral pterygoid muscle, an anatomically variable relationship), conventionally divided into three parts based on this relationship to lateral pterygoid.

First (mandibular) part: Branches include the middle meningeal artery (ascends through foramen spinosum, the classic vessel injured in extradural haematoma), the inferior alveolar artery (accompanies the inferior alveolar nerve into the mandibular canal), and smaller branches to the ear/deep temporal region.

Second (pterygoid) part: Branches supply the muscles of mastication directly (deep temporal, masseteric, pterygoid branches) and the buccal region.

Third (pterygopalatine) part: Passes through the pterygomaxillary fissure into the pterygopalatine fossa. Its branches supply:

• the maxillary teeth (posterior superior alveolar artery)
• the palate (greater/lesser palatine arteries, descending through the palatine canal)
• the nasal cavity (sphenopalatine artery, the dominant nasal blood supply)
• the infraorbital region (infraorbital artery, continuing through the inferior orbital fissure/infraorbital canal)

Boundaries:

• A small, pyramidal space deep to the infratemporal fossa, bounded by the maxilla (anteriorly), the pterygoid process of the sphenoid (posteriorly), and the perpendicular plate of the palatine bone (medially), communicating with several adjacent regions via multiple foramina/fissures, making it a genuine anatomical "crossroads."

Communications:

• Pterygomaxillary fissure (laterally) → infratemporal fossa (transmits the maxillary artery's third part and its branches entering the fossa).
• Inferior orbital fissure (anteriorly) → orbit (transmits the infraorbital nerve/vessels, and the zygomatic nerve).
• Foramen rotundum (posterosuperiorly) → middle cranial fossa (transmits the maxillary nerve, CN V2, entering the fossa).
• Pterygoid canal (posteriorly, through the sphenoid) → foramen lacerum region/middle cranial fossa (transmits the nerve of the pterygoid canal, carrying both parasympathetic (from the greater petrosal nerve) and sympathetic (from the deep petrosal nerve) fibres to the pterygopalatine ganglion).
• Palatine canal (inferiorly) → oral cavity/palate (transmits the greater and lesser palatine nerves/vessels).
• Sphenopalatine foramen (medially) → nasal cavity (transmits the sphenopalatine artery and the nasopalatine/posterior nasal nerves).

Maxillary nerve (CN V2):

• Passes directly through the pterygopalatine fossa (without synapsing in the ganglion here, simply passing through/alongside it) en route from foramen rotundum to the inferior orbital fissure/infraorbital canal.
• It gives off the zygomatic nerve, which later communicates with the lacrimal nerve, carrying parasympathetic fibres to the lacrimal gland.
• It also gives off small ganglionic branches connecting to the pterygopalatine ganglion, through which its sensory fibres to the nose/palate actually pass, without synapsing.

Pterygopalatine ganglion:

• The largest of the four parasympathetic ganglia of the head, suspended from the maxillary nerve (via its ganglionic branches) but receiving its actual parasympathetic input from a different source.
• The greater petrosal nerve (from CN VII) combines with the sympathetic deep petrosal nerve to form the nerve of the pterygoid canal, reaching the ganglion where the parasympathetic fibres synapse.
• Sympathetic and sensory fibres pass through without synapsing, the same general pattern as the ciliary ganglion.
• Postganglionic distribution: Lacrimal gland (via the zygomatic nerve → lacrimal nerve communicating pathway), and the nasal/palatine mucous glands (via direct branches through the sphenopalatine and palatine foramina).

Maxillary artery branches (within the fossa):

• As (third part): sphenopalatine, greater/lesser palatine, posterior superior alveolar, and infraorbital arteries all arise from or pass through this fossa.

TMJ dislocation:

• Occurs when the mandibular condyle moves anterior to the articular tubercle and becomes "locked" in this position, typically from excessive mouth opening (yawning) or direct trauma.
• It is unable to reduce spontaneously, given the pull of the lateral pterygoid: once the condyle is anterior to the tubercle, the muscle continues to pull it further forward rather than allowing it to return.
• Reduction requires downward and then backward pressure on the mandible to guide the condyle back past the tubercle into the mandibular fossa.

Inferior alveolar nerve block:

• A common dental anaesthesia technique, targeting the nerve as it enters the mandibular foramen on the medial ramus surface.
• It is typically injected near the lingula, a small bony projection just anterior to the foramen that serves as the key palpable/visible landmark for injection technique.
• It anaesthetises the ipsilateral lower teeth, lower lip, and chin (via the mental nerve continuation).
• It commonly also affects the nearby lingual nerve, given its close proximity. This produces the familiar "numb tongue" sensation patients experience alongside numb lip/teeth after dental local anaesthesia.

Lingual nerve injury:

• Can occur during inferior alveolar nerve block injection (direct needle trauma, given its close proximity), third molar (wisdom tooth) extraction (given the nerve's close relationship to the posterior mandible in this region), or submandibular gland/duct surgery.
• It causes loss of general sensation over the ipsilateral anterior two-thirds of the tongue and, given the chorda tympani's peripheral course alongside it, loss of taste.

Spread of infection through deep facial spaces:

• The infratemporal fossa's rich venous connections (pterygoid venous plexus, communicating with the cavernous sinus via emissary veins) provide a potential pathway for deep facial/dental infection to spread intracranially.
• This is analogous to, and in addition to, the more commonly emphasised "danger triangle" facial vein pathway.
• Dental infections in particular, given their proximity to this fossa, carry this theoretical spread risk in severe, untreated cases.
• The more common and more clinically significant risk is localised deep space abscess formation (e.g., masticator space infection, causing trismus from muscle involvement).