Right zygomatico coronoid ankylosis: A rare clinical entity

Trismus is defined as a limitation in the mouth- or jaw-opening ability due to reduced mandibular mobility. Limited mouth opening can be caused by several disorders affecting the masticatory system. Most of them involve the temporomandibular joint (TMJ) and the masticatory muscles. Ankylosis of the TMJ is a common cause for the occurrence of trismus. Ankylosis of the TMJ may be extra- or intra-articular. Zygomatico coronoid ankylosis is a rare type of extra-articular ankylosis. In case of limitation of mouth opening, coronoid process locking may be overlooked, because attention is generally focused on the TMJ. The union between the coronoid process and zygomatic arch may be due to bony ankylosis or fibrous ankylosis. It may follow facial fractures caused by gunshots, treated and untreated fractures of the zygomatic complex, with or without a concomitant fracture of the coronoid process, mandibular fractures, extension of the intracapsular ankylosis or due to the enlargement of the coronoid process. A review of literature has disclosed 15 reported cases of this disorder. The true incidence of this condition may be even higher. Zygomatico coronoid ankylosis may have been encountered by many clinicians, and yet may have been misdiagnosed or overlooked. The present article reports a rare entity of a post-traumatic case of trismus, for a duration of 18 years, diagnosed as right zygomatico coronoid ankylosis.