Fluoroscopy-based navigation for transoral atlantoaxial screw placement

Introduction: Transoral atlantoaxial spine surgery may be indicated if ante rior cervical cord compression associated with odontoid fracture, odontoid nonunion, irreducible atlantoaxial dislocation, neoplasm or spondylitis of the upper cervical spine occurs. Transoral atlantoaxial plate fixation has been described by Harms as a fixation technique after odontoid resection. Y et, screw placement in transoral atlantoaxial plating is demanding. Therefo re, the purpose of this study was to evaluate the efficacy and accuracy of fluoroscopy-based navigation in transoral atlantoaxial screw placement. Mat erials and methods: A transoral approach was performed on four human cadave r specimens. The reference base was inserted at the vertebral body of C2. I n pilot studies appropriate C-arm projections for fluoroscopy-based atlanto axial navigation were defined. A regular C-arm (Exposcop 8000, Ziehm) and a navigation system (Stealth Station, Sofamor Danek) were used. In each spec imen six transoral screws (two screws in the lateral mass of C1, two subart icular screws at C2, two transpedicular screws at C2) were inserted using f luoroscopy-based navigation. Postoperative screw position was determined by three independent investigators using X-ray and CT. Results: All procedure s were successfully completed without major difficulties. All screws in the lateral mass of C1 and all subarticular screws at C2 were placed correctly . However, only two of the anterior transpedicular screws at C2 showed corr ect orientation; four screws violated the foramina of the vertebral artery, two screws the spinal canal. Conclusion: Experimentally, safe transoral sc rew placement of lateral mass screws at C1 and subarticular screws at C2 co uld be achieved using fluoroscopy-based navigation. Presently, the accuracy of fluoroscopy-based navigation is insufficient for safe anterior transped icular screw placement at C2. Further improvements in visualisation of the fluoroscope will help to optimise transoral fluoroscopy-based navigation.