Occult posttraumatic cervical ligamentous instability.

Posttraumatic progressive cervical ligamentous instability and spinal deformity may occur in spite of initially apparently normal spine radiographs. Patients at risk for the development of this problem are generally under 25 years of age and have greater than 1.5 mm of horizontal displacement and greater than 5 degrees of angular displacement on initial cervical roentgenograms. Recent experience with this entity at our institution has led to a reevaluation of the currently existing radiographic criteria for determining ligamentous stability.