Lateral pterygoid muscle

The lateral pterygoid muscle (aka pterygoideus externus, external pterygoid muscle) 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 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.

Actions

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".

Innervation

The muscle is supplied by nerves to lateral pterygoid (one for each head) which arise from the anterior trunk of the mandibular nerve, deep to the muscle. The superior head and the lateral part of the inferior head receive their innervation from a branch of from the buccal nerve. The medial part of the lower head has a branch arising directly from the anterior trunk of the mandibular nerve.