C1 Fractures Workup
- Author: Mark R Foster, MD, PhD, FACS; Chief Editor: Jeffrey A Goldstein, MD more...
Cervical spine radiographs are routinely obtained in the emergency department for patients with a history of pain or of trauma, and they are mandatory for the nonresponsive patient, who is unable to report pain. These radiographs specifically include the open mouth view (see the image below).
After confirmation that neutral rotation is present and the radiograph is reliable (eg, as determined by looking at the incisor teeth to confirm lack of rotation of the head), the odontoid should appear symmetrically centered between the lateral masses. A C1 fracture is often associated with lateral displacement; thus, if the ring of C1 overhangs or extends laterally more than 6.9 mm over the lateral mass, a fracture of the ring of C1 is established. However, less excursion does not exclude this fracture, particularly if minimally displaced in the supine patient.
The lateral view is also crucial because the atlanto-occipital membranes may be disrupted and an occipitoatlantal dislocation may be observed; the normal anatomy must be confirmed. If any suspicion of disruption or dislocation exists, traction must be avoided, as well as any subsequent flexion-extension maneuvers or inappropriate manipulation, until that possibility can be excluded.
The odontoid should be well imaged from the lateral view; any lack of alignment or discontinuity that suggests fracture also suggests instability of the upper cervical spine, which may be associated with a C1 fracture but indicates very significant instability, requiring immobilization of the occipitoatlantoaxial complex.
On the lateral view, the Power ratio may be used to evaluate for possible atlanto-occipital dislocation: a ratio greater than 1 of the basion to the posterior arch of C1 (BC) over the anterior arch of C1 to the opisthion (AO) is suspicious for anterior dislocation.
If the ring is not clearly observed to overhang but asymmetry is present between the atlas and the odontoid, a C1-2 problem may be present, particularly atlantoaxial rotary subluxation, which may be a result of one of the facets between these 2 vertebrae being displaced or locked in a dislocated position.
Unfortunately, a possible C1-2 instability, particularly the cock robin position of the head that may be present with displacement of C1 on one side (anteriorly is most common), makes obtaining the standard open mouth and other radiograph views difficult. Computed tomography (CT; see the images below) facilitates those investigations wherein thin cuts best demonstrate the pattern of disruption for evaluating the location and displacement of suspected fractures of C1.
Unilateral posterior displacement of the atlas also produces the cock robin position, but this displacement is usually without a fractured dens. In trauma cases, most commonly, a unilateral combined anterior and posterior subluxation occurs when the transverse ligament is disrupted. The C1 ring may displace anteriorly and reduce the space available for the spinal cord.
Arteriography may be essential and emergent for any suspected vascular compromise or symptoms consistent with a vascular insult to detect occlusion, thrombosis, or intimal tear. Subtraction angiography may also help evaluate collateral circulation. If any circulatory problems are diagnosed, immediate anticoagulation with heparin prevents further extension of thrombosis, and administration of oxygen maintains cerebral oxygenation.
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