Anatomy & Histology · single question
A patient's jaw deviates to the LEFT upon opening. Which muscle is most likely affected?
Show answer and explanation
Correct answer: D. Left lateral pterygoid
During mouth opening, both lateral pterygoid muscles contract to translate the condyles forward (protrude the mandible). If one lateral pterygoid is weak or not functioning, the contralateral (working) side pulls the mandible toward the affected side. Deviation to the LEFT means the LEFT lateral pterygoid is NOT working properly — the right side pulls unopposed, swinging the chin leftward.
- A. INCORRECT. The medial pterygoid elevates and medially deviates the mandible — it is not the primary muscle responsible for jaw deviation on opening.
- B. INCORRECT. If the RIGHT lateral pterygoid were affected, the jaw would deviate to the RIGHT (toward the affected side), not the left.
- C. INCORRECT. The medial pterygoid is not the primary muscle tested by jaw deviation on opening.
- D. CORRECT. The jaw deviates toward the AFFECTED (weak) side during opening. Left deviation = left lateral pterygoid dysfunction. The intact right lateral pterygoid pulls the jaw to the left unopposed.
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