Myositis Ossificans of the Masseter Muscle: A Rare Post-traumatic Case

Post-traumatic myositis ossificans of the masseter is an uncommon cause of severe trismus without a standardized management pathway. A 23-year-old man developed progressive jaw stiffness six months after facial trauma, with maximal interincisal opening <10 mm. Imaging demonstrated mature heterotopic ossification bridging the mandibular ramus and zygomatic arch. Excision of the ossified masseter was performed via a combined intraoral and external approach. Trismus recurred within three months, and re-operation through the prior incision removed residual ossification with coronoidectomy. No adjuvant therapy was used; supervised jaw-opening physiotherapy was instituted. Early postoperative improvement was observed, and at approximately two months after the second procedure, mouth opening reached about three finger breadths with ongoing exercises and no clinical evidence of recurrence. This case underscores that timely recognition of masseteric myositis ossificans and tailored stepwise management, including coronoidectomy when indicated, can restore function and meaningfully improve quality of life.