Torticollis is a common presenting feature of FOP (in about 80%), the head is tilted to one side and there are painful swelling in the region of the sternocleidomastoid muscle.
Flexion of the neck is limited when the ligamentum nuchae ( a ligament that extends from the skull to the seventh cervical vertebrae) is involved.
The mobility of the temporomandibular joint can be diminished when the masseter muscle is involved.