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Background Context: The mechanical strength provided by internal fixation is crucial for maintaining reduction and facilitating bony fusion. Though satisfactory results with the C1-C2 technique have been acquired in most clinical reports, the related problems of fusion delay and pseudarthrosis still exist. To increase the chance of bony fusion, a transverse connector (TC) is frequently used to augment torsional stiffness of thoracolumbar screw/rod constructs. Nevertheless, the clinical implication of TC in the management of atlantoaxial dislocation (AAD) and basilar invagination (BI) remains largely unknown.Purpose: To evaluate the effects of TC application on C1-C2 screw-rod constructs based on consecutive adult patients with AAD and BI in a single institution over a 10-year period.Study Design: A retrospective study.Patient Sample: Patients with AAD and BI, who were treated with posterior C1-C2 screw-rod technique with or without TC usage from June 2007 to June 2017 at a single institution.Outcome Measures: The radiological measurements included the anterior atlantodental interval (AADI), posterior atlantodental interval (PADI), height of odontoid process above Chamberlain line, and cervicomedullary angle (CMA). Patients' neurologic status was evaluated with the Japanese Orthopaedic Association (JOA) score. Fusion status was evaluated at different follow-up periods.Methods: We compared the difference of clinical, radiological, and surgical outcomes between the TC and NTC groups postoperatively.Results: In total, there were 149 consecutive patients in the TC group and 168 patients in the NTC group. On average, 1.2 TCs per patient were used in the TC group. No significant differences were identified for operative time and blood loss between groups. There was also no statistical difference in the radiological measurements of AADI, PADI, Chamberlain line, and CMA between the TC and NTC groups preoperatively and postoperatively. A significantly higher JOA score was obtained in the TC group than that in the NTC group postoperatively. The fusion rates were higher in the TC group than those in the NCT group at the early stage postoperatively (3 and 6 months; p<.01).Conclusions: Use of TCs seems to improve bony fusion and neurologic outcomes in the treatment of AAD and BI with C1-C2 screw-rod technique. [ABSTRACT FROM AUTHOR]

Abstract: Background context: Treatment of chronic and irreducible atlantoaxial dislocation (AAD) with ventral compression is challenging for surgeons. The main procedures are occipitocervical/C1–C2 fusion after transoral odontoidectomy or release of the periodontoid tissues. These surgical procedures, which are performed simultaneously or intermittently, have many disadvantages that may discount their effectiveness. Therefore, a more effective way to achieve surgical reduction and to keep solid stability with only a single procedure is needed. Purpose: We describe a technique to reduce chronic and irreducible AAD with C1 lateral mass and C2 pedicle screw and rod system. Study design: This was a retrospective case series. Patient sample: Our sample comprised 26 patients (9 men and 17 women) with irreducible AAD who ranged in age from 15 to 54 years (mean, 35 years). Outcome measures: Patients' neurologic status was evaluated with the Japanese Orthopedic Association (JOA) scale. Methods: Twenty-six symptomatic patients underwent posterior realignment and reduction through the C1 lateral mass and C2 pedicle screw and rod system. The proposed mechanism of reduction is that the implanted screws and rods between C1 and C2 acting as a lever system drew C1 backward and pushed C2 downward and forward after removing circumambient obstruction and scars and thoroughly releasing the facet joints. The preoperative and postoperative JOA score, the extent of reduction, and the conditions of C1–C2 bony fusion were examined. Results: No neurovascular injury occurred during surgery. Follow-up ranged from 6 to 40 months (mean 20.7 months). Radiographic evaluation showed that solid bony fusion was achieved in all patients, and that complete reduction was attained in 18 patients and partial reduction (>60% reduction) in 8 patients. The mean postoperative JOA score at last follow-up was 15.7, compared with the preoperative score of 12.1 (p<.01). Conclusions: This C1–C2 screw and rod system provides reliable stability and sufficient reduction of the anatomic malalignment at the craniovertebral junction and meanwhile retains the mobility of atlanto-occipital joints in the treatment of chronic and irreducible AAD. Sophisticated skills, thorough release of the facet joints, and intraoperative protection of the vertebral artery are key points to accomplish this technique. [Copyright &y& Elsevier]

To evaluate the usefulness of 3-dimensional (3D) printed models as an aid for the treatment of complex CVJ anomalies. 3D printed models were fabricated for 21 patients with complex CVJ anomalies, including vertebral artery anomaly, thin C2 pedicle, vertical atlantoaxial facet joint, or rotational dislocation combined with atlantoaxial dislocation and basilar invagination. Preoperative planning, surgical simulation, and intraoperative reference were achieved using the 3D model during the surgical treatment. The usefulness of 3D printed models, and postoperative clinical and radiological outcomes were assessed. Direct posterior reduction and atlantoaxial fixation were achieved in 19 patients. Transoral odontoidectomy followed by posterior fixation was implemented for 2 patients with vertical facet joint and rotational dislocation. All screws were safely inserted with no complication, and 90% patients achieved a >60% reduction of both horizontal and vertical dislocation. Clinical symptoms improved in all patients, with the averaged Japanese Orthopedic Association scores increasing from 11.14 to 14.43 (P < 0.01). The patient-specific 3D printed model would be an effective tool for evaluation of the reducibility of the atlantoaxial dislocation and basilar invagination, decision making in choosing the optimal surgical approach and way of fixation, and precise placement of the screw while protecting the vertebral artery and spinal cord. The risk of neurovascular injury was minimized, and encouraging outcomes were achieved with the aid of this technique. [ABSTRACT FROM AUTHOR]

Occipitalization of the atlas (OA) often is associated with atlantoaxial dislocation and basilar invagination. The purpose of this study is to determine the biomechanical difference between normal and OA conditions in the craniovertebral junction and to further explore the rationale for development of atlantoaxial dislocation and basilar invagination using the finite element model (FEM). A ligamentous, nonlinear, sliding-contact, 3-dimensional FEM of the occipitoatlantoaxial complex was generated. Validation of the model was accomplished by comparing kinematic predictions with experimental data. We defined the atlantooccipital joint as a tie contact to simulate the OA deformity. The range of motion and the value of the maximum Von Mises stress were compared between the intact and OA models. We found all of the predicted data in the intact FEM fell within 1 standard deviation of the cadaver data for all 6 loadings. The OA simulation significantly reduced the overall range of motion of the occipitoatlantoaxial complex at all loadings. The maximum Von Mises stress was predicted to increase at the transverse ligament and the superior articular facet of the axis for all the flexion, extension, lateral bending, and axial rotation loadings. The OA could result in hypermobility of the atlantoaxial segment and cause overstress in the transverse ligament and the lateral atlantoaxial joints. These changes explain the pathogenesis of atlantoaxial dislocation and basilar invagination associated with OA. Follow-up should be scheduled regularly due to the nature of the dynamic development of atlantoaxial dislocation and basilar invagination. [ABSTRACT FROM AUTHOR]