Friday, September 28, 2018 4:05 PM–5:05 PM abstracts: new concepts: cervical spine: 245. Risk of atlantooccipital joint injury during C1 pedicle screw insertion: a CT-based morphology study of atlas

Abstract

BACKGROUND CONTEXT C1 pedicle screw technique is increasingly popular for atlantoaxial screw-rod fixation. Many authors have reported anatomic studies for C1 pedicle screw insertion. Most of them focused on whether the pedicle screw would injury transverse foramen, vertebral groove and spinal dura. No study evaluates the risk of atlantooccipital joint injury during C1 pedicle screw insertion yet. PURPOSE To evaluate the risk of atlantooccipital joint injury when inserting C1 pedicle screw and analyse the related anatomic factors. STUDY DESIGN/SETTING A CT-based morphology study. PATIENT SAMPLE Two hundred study units. OUTCOME MEASURES Atlantooccipital joint penetration by the pedicle screw was defined as atlantooccipital joint injury. METHODS One hundred thin-cut upper cervical spine computed tomography (CT) scans which met our inclusion criteria were acquired. The sagittal plane of the planned C1 pedicle screw trajectory was reconstructed. Each sagittal plane was considered as a single unit. And then a 3.5-mm-diameter cylinder was draw to simulate a 3.5-mm-diameter pedicle screw inserting into atlas on each sagittal plane. Atlantooccipital joint penetration by the pedicle screw was defined as atlantooccipital joint injury. Those sagittal planes with atlantooccipital joint injury were carefully studied and the morphology of the atlas was observed and analyzed. RESULTS Two hundred study units were obtained from one hundred upper cervical spine CT scans. Virtual C1 pedicle screw insertion showed that atlantooccipital joint injury occurred in thirty-two units (16%) with bilaterally in eleven patients and unilaterally in ten patients. Over-concave superior articular facet of atlas, high junction of C1 pedicle and C1 lateral mass, and over-cephalad incline of C1 pedicle were observed in units with atlantooccipital joint injury. CONCLUSIONS Two hundred study units were obtained from one hundred upper cervical spine CT scans. Virtual C1 pedicle screw insertion showed that atlantooccipital joint injury occurred in thirty-two units (16%) with bilaterally in eleven patients and unilaterally in ten patients. Over-concave superior articular facet of atlas, high junction of C1 pedicle and C1 lateral mass, and over-cephalad incline of C1 pedicle were observed in units with atlantooccipital joint injury.