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Oral Surgery · single question

Which muscle is responsible for trismus as a complication of inferior alveolar nerve block (IANB) injections?

  1. Lateral pterygoid
  2. Medial pterygoid (deposition of anesthetic or hematoma in the muscle)
  3. Masseter
  4. Temporalis
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Correct answer: B. Medial pterygoid (deposition of anesthetic or hematoma in the muscle)

  • A. The lateral pterygoid is not in the typical IANB injection pathway and is not the most common cause of post-IANB trismus.
  • B. Correct. Trismus after IANB is most commonly caused by anesthetic deposited INTO the medial pterygoid muscle rather than the pterygomandibular space. This causes: (1) muscle injury/irritation, (2) possible hematoma, (3) inflammation — all leading to painful restriction of mouth opening (trismus). The medial pterygoid lies just medial to the usual injection site.
  • C. The masseter is on the buccal/external aspect — not accessed by the IANB injection technique.
  • D. The temporalis inserts into the coronoid process — not in the IANB injection pathway.

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