Posterior C1-C2 fusion with polyaxial screw and rod fixation

Abstract

Study design: A novel technique of atlantoaxial stabilization using individual fixation of the C1 lateral mass and the C2 pedicle with minipolyaxial screws and rods is described. In addition, the initial results of this technique on 37 patients are described.

Objectives: To describe the technique and the initial clinical and radiographic results for posterior C1-C2 fixation with a new implant system.

Summary of background data: Stabilization of the atlantoaxial complex is a challenging procedure because of the unique anatomy of this region. Fixation by transarticular screws combined with posterior wiring and structural bone grafting leads to excellent fusion rates. The technique is technically demanding and has a potential risk of injury to the vertebral artery. In addition, this procedure cannot be used in the presence of fixed subluxation of C1 on C2 and in the case of an aberrant path of the vertebral artery. To address these limitations, a new technique of C1-C2 fixation has been developed: bilateral insertion of polyaxial-head screws in the lateral mass of C1 and through the pars interarticularis into the pedicle of C2, followed by a fluoroscopically controlled reduction maneuver and rod fixation.

Methods: After posterior exposure of the C1-C2 complex, the 3.5-mm polyaxial screws are inserted in the lateral masses of C1. Two polyaxial screws are then inserted into the pars interarticularis of C2. Drilling is guided by anatomic landmarks and fluoroscopy. If necessary, reduction of C1 onto C2 can be accomplished by manipulation of the implants, followed by fixation to the 3-mm rod. For definitive fusion, cancellous bone can be added. No structural bone graft or wiring is required. In selected cases, e.g., C1-C2 subluxation or fractures in young patients in whom only temporary fixation is necessary, the instrumentation can be removed after an appropriate time. Because the joint surfaces stay intact, the patient can regain motion in the C1-C2 joints.

Results: Thirty-seven patients underwent this procedure. No neural or vascular damage related to this technique has been observed. The early clinical and radiologic follow-up data indicate solid fusion in all patients.

Conclusion: Fixation of the atlantoaxial complex using polyaxial-head screws and rods seems to be a reliable technique and should be considered an efficient alternative to the previously reported techniques.