Accuracy of Pedicle screw insertion using a new intraoperative cone-beam ct imaging technique: retrospective analysis of 586 screws

Abstract

INTRODUCTION Pedicle screw placement is a widely used procedure for the treatment of spine pathologies including trauma, scoliotic deformities, infection, degenerative and malignant diseases. Inaccurate screw placement with a pedicle breach can lead to spinal cord, visceral and vascular injuries, with complications in terms of patient survival. Clinical studies have demonstrated the feasibility of achieving clinically accurate placement of pedicle screws with the aid of assistive technologies including intraoperative imaging systems, navigation systems, robots, and 3D-printed mechanical guides (Tian 2011). Assessment of pedicle screw placement accuracy is usually carried out in postoperative CT scans (Motiei-Langroudi 2015), thereby making it impossible to detect pedicle breach intraoperatively. New techniques have been adapted to detect pedicle breach intraoperatively and to allow for direct re-positioning of these misplaced screws (Santos 2012), thereby helping to reduce the radiation dose by eliminating the need for postoperative CT scans. This retrospective study aims to assess accuracy of pedicle screw placement using a new intra-operative cone-beam CT (CBCT) imaging technique, and to compare the efficacy of this technique with conventional postoperative CT scans for pedicle breach detection. MATERIALS AND METHODS In 102 patients, 586 pedicle screws were inserted over a 21 month period. The new intraoperative CBCT imaging technique consisted of a robotic interventional angiography system (Artis Zeego, Siemens Healthcare, Forchheim, Germany) equipped with CBCT software applications (DynaCT, Siemens Healthcare, Forchheim, Germany) which has been recently adapted for spine surgeries. In all patients, intraoperative CBCT scans (Fig. 1) were acquired after all screws were inserted, and retrospectively reviewed by the orthopaedic surgeons for pedicle breach detection and grading. Of the 586 inserted screws, placement assessment of 239 screws were also carried out in conventional postoperative CT scans using the same grading system. Reliability tests computing Cohen’s Kappa coefficient and Gwet’s coefficient were performed to compare the CBCT imaging technique with the conventional postoperative CT scans for assessing screw placement accuracy and detecting pedicle breach. Sensitivity, specificity, positive and negative predictive values of the CBCT imaging technique to assess screw placement accuracy were measured, assuming that postoperative CT scans are the gold standard for assessing such accuracy. RESULTS Of the 586 inserted pedicle screws (Fig. 2), 496 (84.6%) were placed within the pedicle without any breach, 24 (4.1%) were in-out-in screws with a lateral breach but with the screw tip inside the vertebral body, 21 (3.6%) had a medial breach 4 mm, 5 (0.9%) had a lateral breach, and 26 (4.4%) had an anterior breach. Seventeen screws (2.9%) were revised intraoperatively. Kappa and Gwet’s coefficients on screw placement assessment carried out in intraoperative CBCT and in conventional postoperative CT scans were 0.80 and 0.93, respectively. Sensitivity and specificity of the intraoperative CBCT imaging technique, considering that the postoperative CT imaging is the gold standard, were 0.77 and 0.98, respectively. Positive and negative predictive values were 0.91 and 0.96, respectively. DISCUSSION This study is the first to assess accuracy of pedicle screw placement using the new intraoperative Artis Zeego CBCT imaging system. Screws placed within the pedicle without any breach were considered accurate. In-out-in screws with a lateral breach but with the screw tip inside the vertebral body can also be considered accurate thanks to relevant mechanical stability (Husted 2004). The cumulative rate of “accurate” screws in the present study is consistent with the findings of clinical and cadaveric studies that investigated the accuracy of pedi