Fibrodysplasia Ossificans Progressiva: A Case Report with Pseudo-Ankylosis of the Temporomandibular Joint.

Fibrodysplasia ossificans progressiva (FOP) is a rare condition characterized by progressive heterotopic ossifications and congenital hallux valgus deformities. The common underlying genetic cause is an mutation, resulting in altered bone morphogenetic protein (BMP) regulation. Trauma and/or minor procedures aggravate the abnormal bony formation in soft tissues. This report presents a 3-year-old child with this condition who presented pseudo-ankylosis of the temporomandibular joint (TMJ) after minor craniofacial trauma. Abnormal ossification in the medial pterygoid muscle was identified as the causative abnormality for the presentation with trismus.