Combined occipitoatlantoaxial hypermobility with anterior and posterior arch defects of the atlas in Pierre-Robin syndrome.

Combined occipitoatlantoaxial instability of the cervical spine occurred in a 8-year-3-month old boy with Pierre-Robin syndrome. He also had failure of ossification of both the anterior and posterior arches of the atlas. An in situ fusion from the occiput to C2 restored cervical spine stability. This case is discussed in relation to other hypermobility and instability syndromes of the cervical spine.