The lateral pterygoid has two heads: the superior head attaches to the articular disc and capsule of the TMJ via a short superior tendon, and the inferior head inserts via a flat tendon into the pterygoid fovea on the anterior condylar neck. The superior head's disc attachment means lateral pterygoid contraction during mouth opening also retracts the articular disc anteriorly. The tendon fibres are continuous with the anterior capsule and the posterior disc.
The lateral pterygoid tendon-disc attachment is central to the biomechanics of TMJ internal derangement. In anterior disc displacement (the most common TMJ disorder), the superior lateral pterygoid head pulls the disc further anteriorly when the muscle contracts, perpetuating the displacement. Lateral pterygoid spasm produces jaw deviation to the contralateral side on opening, a classic clinical sign of unilateral lateral pterygoid hypertonicity. MRI of the TMJ demonstrates the disc-condyle relationship and the lateral pterygoid attachment zone.
Hypertonicity or spasm of the superior lateral pterygoid head chronically pulls the articular disc anteriorly beyond the condylar head, producing clicking on mouth opening when the condyle recaptures the disc and a closed lock when the condyle cannot recapture it, managed by splint therapy, physiotherapy, and arthroscopic disc repositioning.
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