Fracture Type

Fracture type and the amount of displacement are important factors in selecting a patient for surgery.

According to the classification of Anderson and D’Alonzo, type II and “shallow,” or rostral, type III fractures are appropriate for odontoid screw fixation.1 Apfelbaum et al. suggested a subclassification of type II fractures according to the orientation of the fracture line.6 According to this subclassification, horizontal and oblique anterosuperiorly oriented fracture lines on the sagittal plane predict higher fusion rates than oblique anteroinferiorly oriented fracture lines. This subdivision, however, has not been addressed in series by other authors. Given that the overall fusion rate in the oblique anteroinferior group is still 75%, this information is probably not indispensable, but it can be of help in making difficult decisions.6

The axis needs to be carefully examined for additional fractures or fracture lines, as this could have negative repercussions on screw purchase. The same goes for the fractured dens fragment. Type IIA fractures (comminution of the dens) might not warrant sufficient screw purchase, which is particularly important at the cortical tip of the dens that needs to be engaged by the screw.3–6

As far as the amount of displacement is concerned, the literature shows that values > 4 to 6 mm seem to represent a threshold beyond which the risk of nonfusion becomes significantly and probably unacceptably high with conservative treatment.13–15

Finally, a magnetic resonance imaging scan of the area to check for integrity of the transverse ligament is indicated even though not indispensable, in our opinion, due to the relatively low association of ligamentous rupture with an odontoid fracture. However, because of the common availability of this imaging technique and its routine use in spinal trauma in many centers, particular attention to the state of the transverse ligament should be paid. In case of a clear rupture, this would represent a contraindication to odontoid screw fixation.

Timing of Surgery

The general rule of the earlier the fusion, the better surely also applies to this type of procedure. Evidence from the literature seems to suggest that there are no differences in fusion rates during the first 6 months, whereas after 18 months, fusion rates clearly drop. This information is based on a series published by Apfelbaum et al. and has led to a division of patients as “early” or “late.” The fact that there is essentially no information on patients who had a fracture between 6 and 18 months is because such patients were not included in that study (or, to our knowledge, in any other study).5–7,14,15

Knowing, however, that it apparently does not make a difference whether a patient undergoes fusion immediately or after 6 months is surely helpful, as it gives the surgeon the option of trying conservative treatment in those patients deemed appropriate while still having time to do fixation should that treatment fail.

Age

Although there is some controversy in the literature, generally it is agreed that the patient’s age influences the outcome of odontoid screw fixation.6–10,14–26 The younger the patient, the more likely it is that fusion may be obtained by external immobilization. Sherk et al. reported a series of 35 children (younger than 7 years), with only 1 failed fusion after halo immobilization.24 The older the patient, the more the fusion rate seems to correlate inversely. Lennarson et al. showed in one of their studies that the nonunion rate in patients older than 50 years is 21 times higher than in those who are younger.15

Even if one tends to not believe in the inverse relationship between age and fusion rate in conservative management, the important message surely seems to be that older patients do at least as well as younger patients with surgery; this can be important when tailoring a specific treatment plan. In older patients, compliance with external immobilization such as a halo jacket and the resulting overall movement restriction can have significant negative repercussions on outcome and the patient’s general health. We therefore tend to favor surgery in older patients, taking only unfitness for general anesthesia and severe osteopenia as contraindications.

Patient Positioning and Setup

Under general anesthesia, the patient is intubated with an endotracheal endoscope. This can be accomplished via either the nose or the mouth, making sure that a nonarmored tube is used. The patient is then positioned neutrally supine on the operating table. The patient’s head can be secured in a three-pin fixation device, rest on a horseshoe, or positioned directly on the operating table with a towel roll under the neck. What is most important is that the head remains immobile throughout the procedure.

Once the patient is thus positioned, two C-arm image intensifiers are brought in and centered on the C1–C2 complex, with one obtaining a lateral view and the other an anteroposterior view ( Fig. 13.1 ).

In case of dislocated fracture, the patient’s head should be gently manipulated under lateral fluoroscopy in an attempt to reduce the fracture as much as possible, then secured in the desired position. The two C-arms should remain in position during the entire procedure, as frequent imaging is crucial during the various steps. To obtain a good anteroposterior view, it is often helpful to obtain open mouth views by inserting a radiolucent mouth opener or bite blocks in the patient’s mouth.

Once these steps are accomplished, the C-arms are both in a position to obtain good views, and the patient’s head is well secured and in the correct position to obtain as much fracture reduction as possible, the patient and the equipment are draped in the usual fashion.