The coronoid process is the anterior projection of the mandibular ramus, a thin triangular bony projection that serves as the insertion of the temporalis muscle. It lies anterior to the condylar process, separated by the mandibular notch (sigmoid notch) through which the masseteric vessels and nerve pass. The coronoid process sits within the temporal fossa and passes beneath the zygomatic arch during wide mouth opening.
Coronoid process hyperplasia is a rare cause of progressive trismus, where an abnormally elongated coronoid impinges on the inner surface of the zygomatic arch during mouth opening. It presents as painless progressive limitation of jaw opening without joint pathology, often bilateral and diagnosed on CT by demonstrating the enlarged coronoid contacting the zygomatic arch. Coronoidectomy via an intraoral approach restores mouth opening. Coronoid fractures are uncommon but can occur with temporal bone fractures or zygomaticomaxillary complex injuries.
Elongation of the coronoid process causing impingement against the zygomatic arch during mouth opening produces progressive painless trismus, managed by coronoidectomy through an intraoral approach with immediate improvement in opening.
Isolated coronoid fractures from direct temporal blow or as part of zygomaticomaxillary complex injury rarely require fixation given the temporalis muscle usually holds the fragment adequately; significant displacement or functional deficit from temporalis detachment is treated with ORIF.
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