C1 lateral mass screw placement in occipitalization with atlantoaxial dislocation and basilar invagination: a report of 146 cases.

Study Design: Retrospective study of 146 patients with the diagnosis of occipitalization, atlantoaxial dislocation (AAD) and basilar invagination, using a novel surgical treatment strategy.
Objective: To introduce a novel fixation and reduction technique.
Summary of Background Data: Atlas occipitalization associated with basilar invagination often result in fixed AAD that need reduction and occipitocervical fixation. The widely used occipitocervical fixation with suboccipital screws has several limitations such as the poor screw purchase in maldevelopment of the occipital bone, limited area available for implants in previous suboccipital craniectomy. The placement of occipitalized C1 lateral mass screw is an alternative option.
Methods: From June 2007 to June 2013, 146 patients of occipitalized atlas with fixed AAD and basilar invagination, underwent fixation and reduction via C1 lateral mass and C2 pars/pedicle screw.
Results: A total of 143 patients achieved the follow-up in the range from 6 months to 4 years (average, 30 mo). Neurological improvement was seen in all the 143 patients, with the averaged Japanese Orthopedic Association scores increasing from 11.6 to 15.5. Radiographical evaluation showed that solid bony fusion was achieved in all patients, and complete reduction was attained in 95 patients, and partial reduction (>60%) in 40 patients, and no effective reduction in 8 patients who had additional transoral decompression. Magnetic resonance imaging demonstrated that the ventral cervicomedullary compression was relieved in all patients.
Conclusion: Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue situation where more conventional stabilization alternatives are not technically possible, or as routine occipitocervical stabilization. It provides firm stabilization offering an optimum situation for bony fusion, and meanwhile the effective reduction of fixed AAD and basilar invagination. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization with this technique.