Location and Structure
- Origin (O): arises from the roof of the infratemporal fossa (fossa infratemporalis) and the lateral plate of the pterygoid process.
- Insertion (I): fibers course toward the neck of the mandibular condyle, and some fibers insert directly into the capsule and articular disc of the temporomandibular joint (TMJ).
Anatomically, the muscle is divided into two portions — superior and inferior heads — which have significant differences in biomechanics.
Function and Biomechanics
The lateral pterygoid muscle belongs to the muscles of mastication, but its primary role is not elevation, rather shifting the mandible in different planes:
- Protrusion: the muscle pulls the mandible forward. In doing so, the condyles along with the discs move downward and forward along the slopes of the articular tubercles (forming the sagittal condylar path with a Gysi angle averaging 33°).
- Laterotrusion (lateral excursions): during unilateral contraction, the mandible shifts to the side opposite the contracting muscle. On the balancing side, the mandibular condyle moves downward, forward, and medially, while on the working side, it rotates around its vertical axis.
- Reciprocal function of the heads: the superior and inferior heads function reciprocally. The superior head controls the position of the articular disc. When the mandibular condyle moves posteriorly, it performs an eccentric contraction (it lengthens to decelerate its stretch rather than shortening), returning the disc to its initial position. The muscle tone largely depends on dental occlusion.
Topography and Neighboring Structures
The muscle is a key landmark of the deep facial region and contributes to the formation of important fascial spaces:
- Interpterygoid space (spatium interpterygoideum): located between the lateral and medial pterygoid muscles. Branches of the mandibular nerve pass through here, enclosed within the interpterygoid fascia.
- Pterygomandibular space: the lateral pterygoid muscle forms its superior boundary. Inflammatory processes (abscesses and phlegmons) in this zone arise from infections originating from the lower molars or as a complication of inferior alveolar nerve block anesthesia, causing inflammatory trismus—a marked limitation in mouth opening.
- Relation to nerves: the buccal nerve (n. buccalis) emerges directly between the two heads of the lateral pterygoid muscle. The deep temporal nerves loop over the superior border of the muscle, and the inferior alveolar nerve (n. alveolaris inferior) passes deep to it. Surgical access to the deep branches of the trigeminal nerve requires dissection of this muscle.
Blood Supply and Innervation
- Blood supply: provided by pterygoid branches (rr. pterygoidei) from the second (pterygoid) part of the maxillary artery (a. maxillaris). The maxillary artery itself—one of the most complex vessels of the head—courses around the neck of the condylar process and runs transversely across the superficial surface of the lateral pterygoid muscle or between it and the temporalis muscle. The buccal artery (a. buccalis) may also lie on the superficial surface of the muscle.
- Innervation: supplied by motor branches of the mandibular division of the trigeminal nerve ($V_3$) — the mandibular nerve (n. mandibularis). The trunk of this nerve is short (up to 0.5 cm), and its branches course within the interpterygoid space.