A patient develops trismus following an inferior alveolar nerve block. Which muscle is most commonly responsible?

Correct answer: A. Medial pterygoid

• A. CORRECT. The needle path for an IAN block passes through or immediately adjacent to the MEDIAL PTERYGOID, and this muscle is the classic site of post-injection trismus. Trauma from the needle, intramuscular haemorrhage, or irritation from the anaesthetic solution causes myospasm and a haematoma that organises into fibrous tissue. Onset is typically 1–6 days after injection, and management is heat, analgesics, gentle jaw exercises, and reassurance — most cases resolve in days to weeks.
• B. The masseter is lateral to the ramus and is not traversed by the IAN block needle, though it can be involved in trismus from infection or extended mouth opening.
• C. The lateral pterygoid is less commonly involved in post-injection trismus; it lies more superiorly and anteriorly relative to the standard needle path.
• D. Temporalis trismus is more often associated with infratemporal infection or myofascial pain than with the IAN block itself.

Note: Persistent trismus beyond 2 weeks, or trismus with fever and swelling, warrants a look for infection rather than simple myospasm.