Increase of the clivus-canal angle in patients with basilar invagination, without atlantoaxial displacement, treated with a simple maneuver of indirect decompression of the odontoid with the head clamp, during posterior occipitocervical arthrodesis

BACKGROUND: Basilar invagination (BI) can be defined as the insinuation of the content of the craniovertebral junction through the foramen magnum toward the posterior fossa. BI is a prevalent condition in Northeast Brazil. The present study describes the changes in the clivus-canal angle (CCA) in the postoperative period in patients with symptomatic BI operated by a posterior approach, using a simple technique of indirect reduction of the odontoid associated with occipitocervical fixation. METHODS: Patients underwent radiological evaluations by magnetic resonance imaging in the pre and postoperative periods, where the height of the odontoid tip was measured in relation to the Chamberlain line and the ACC. All patients underwent posterior occipitocervical fixation with specific maneuvers of distraction and extension of the cephalic segment with the aid of a head clamp with three fixation points for anterior reduction of the odontoid. RESULTS: Among the 8 patients evaluated in the series, all had increased ACC in the postoperative period, with a mean of 14.81 ± 1.54°, and statistically significant difference between the pre and postoperative periods (P < 0.05). CONCLUSION: The indirect surgical reduction of the odontoid process by a posterior approach through the manipulation (distraction-extension) of a “Mayfield” type of head clamp followed by occipitocervical fixation proved to be effective in improving the ACC, being easily reproducible.