[Fracture and dislocation of the atlanto-axial joint after mild trauma in a patient with rheumatoid arthritis].

The importance of the present article lies in the fact that it deals with an infrequent complication in patients with rheumatoid arthritis, because most of the fractures that occur on the odontoid process are non-traumatic in origin. Dislocations of the atlantoaxial joint have an incidence that goes from 19% to 70%, according to the studies consulted. Normally, the space between the odontoid process, in its anterior border, and the posterior border of the anterior arch of the atlas is 2.5 mm, and remains constant in flexion and extension. When the transverse ligament is lax, this space increases in size. In rheumatoid arthritis, the anterior part of the odontoid process can be eroded in 14%–35% of cases and is usually related to dislocation.