Lateral pterygoid muscle

The lateral pterygoid muscle, also known as pterygoideus externus or external pterygoid muscle, is one of the muscles of mastication. 

Gross anatomy

The lateral pterygoid is a short, thick muscle, somewhat conical in form, which extends almost horizontally, posteriorly and laterally between the infratemporal fossa and the condyle of the mandible. It arises by two heads: an upper (superior) and a lower (inferior). 

The superior part arises from the lower part of the lateral surface of the greater wing of the sphenoid bone and from the infratemporal crest. It inserts in the TMJ capsule and TMJ disc.

The inferior part arises from the lateral surface of the lateral pterygoid plate and inserts into a depression in front of the neck of the condyle of the mandible; the pterygoid fovea.

Innervation

The muscle is supplied by the paired nerves to lateral pterygoid (one for each head) which arise deep to the muscle from the anterior division of the mandibular nerve (CN V₃).

Action

The superior part is active during retrusion (opposite of protrusion) and ipsilateral jaw movement. It is also essential in pulling the capsule and disc forward during mouth opening, thereby maintaining normal relationship between the condyle of the mandible and the TMJ disc.

The inferior part is responsible for opening of the mouth, protrusion and contralateral jaw movement.

Hyperactivity of the LPM muscle has been described in TMJ internal derangement, especially with longstanding anterior displacement of the disc without recapture. Thickening of the tendon (inferior part) can give rise to the "double disc sign".