Atlanto-occipital hypermobility.

Hypermobility of the atlanto-occipital joint can be seen following trauma or in a patient with congenital fusion of C1-C2 as a progressive problem. The lateral roentgenogram is the key to the diagnosis, and familiarity with the normal anatomy is necessary. In the trauma setting care should be taken not to increase the dislocation with traction. Treatment by a posterior craniocervical fusion has proved successful in both groups of patients.