CASE HISTORY
This young adult patient presents with neck pain following an MVA. You note an abnormality in the upper cervical spine at C1 & C2. Is this a fracture?
DISCUSSION
Anomalies of the odontoid process are considered uncommon (1) and are usually discovered by the principle “traumatic determinism.” This means that the underlying condition predated the injury and is not caused by this current trauma. These anomalies may be associated with Down’s syndrome, Klippel-Feil syndrome, Morquio’s syndrome, and spondyloepiphyseal dysplasia.
Clinical Features:
Any symptoms the patient may manifest are usually the result of atlantoaxial instability with resultant cord compression; however, if there is compression of the vertebral artery resulting from stretching of the artery during C1 subluxation on C2, then the symptoms may be considerably greater. Increased deep-tendon reflexes, proprioceptive loss, or sphincter incompetence may be encountered. Additionally, compression of the vertebral arteries may result in local thrombosis and vascular occlusion. The thrombus may also serve as a source for emboli to the brain.
Clearly, the combination of os odontoideum with high-velocity injury can produce central cord syndrome or even fatal injury.
Radiologic Features:
The X-ray diagnosis of os odontoideum in a child below the age of 5 years can be made, if there is demonstration of hypermobility of the odontoid process on the body of C2 during flexion and/or extension. In the adult, an X-ray diagnosis is certain, if a smooth, wide, lucent defect is seen to separate the odontoid process from the C2 body at the level of the superior articular processes, and there is an associated stress hypertrophy (enlargement) of the anterior tubercle of the atlas. This finding will not be present in the child, as the biomechanical stresses on the anterior arch of the atlas will not have been present for a long enough period to allow the hypertrophy to develop. Os odontoideum must be differentiated from an acute fracture of the odontoid process. A helpful radiographic sign that may be present and that confirms a developmental defect of the odontoid process is a “molding: of the anterior arch of C1 into the ventral aspect of the odontoid process.
Magnetic resonance imaging is useful in evaluating the spinal cord for angulation, compression, and intramedullary injury (contusion).
Dr. Terry R. Yochum is a second generation chiropractor and a Cum Laude Graduate of National College of Chiropractic, where he subsequently completed his radiology residency. He is currently Director of the Rocky Mountain Chiropractic Radiological Center in Denver, CO, and Adjunct Professor of Radiology at the Southern California University of Health Sciences, as well as an instructor of skeletal radiology at the University of Colorado School of Medicine, Denver, CO. Dr. Yochum can be reached at 1-303-940-9400 or by e-mail at [email protected].
Dr. Chad Maola is a 1990 Magna Cum Laude Graduate of National College of Chiropractic. Dr. Maola is available for post-graduate seminars. He may be reached at 1-727-433-0153 or by email at [email protected].
Reference
1.Yochum, T. R., Rowe, L.J.: Essentials of Skeletal Radiology, 3rd ed., Williams & Wilkins, Baltimore, Maryland, 2005.