Assessment of pedicle perforation by the cervical pedicle screw placement using plain radiographs: A comparison with computed tomography

Study Design: A retrospective study. Objective: To suggest methods for detecting pedicle perforation on the basis of cervical pedicle screw (CPS) position on plain radiographs. Summary of Background Data: No studies have reported correlations between CPS position and pedicle perforation as observed on plain radiographs. This study was performed under the assumption that the detection of pedicle perforation would help to minimize the risks of neurovascular injury and help to obtain stable fixation. Methods: A total of 48 subjects (with 205 screws) who had undergone CPS placement from C3 to C7 were enrolled in this study. To evaluate CPS position, the positions of the screw heads (neutral; the lateral margin of lateral mass cross the polyaxial screw head core, medial, or lateral) and tips (medial to uncovertebral joint [UVJ], within UVJ, or lateral to UVJ) on anteroposterior (AP) radiographs were analyzed. On the postoperative computed tomography, we analyzed the grade of pedicle perforation (grade 0: no PF; 1: < 25%; 2: 20%-50%; 3: > 50% of the screw diameter violation). Grades 0 and 1 were considered to be the correct position. Results: Correct positioning was found for 174 screws (84.9%), and incorrect positioning was found for 31 screws (15.1%). The screw head was placed in a neutral position for 182 screws (88.8%), in the lateral position for 15 screws (7.3%), and in the medial position for 8 screws (3.9%). Of the 182 screws whose heads were in neutral position, 151 (83%) screws whose tips were located medial to the UVJ area were correctly positioned (sensitivity 0.89, specificity 1.0). A significant correlation was observed between the position of the screw tip and the grade of pedicle perforation (P = 0.000). Conclusion: A screw with a head that is located in a neutral position and a tip that is placed medial to the UVJ area on plain radiographs is considered to be in the safest position. A tip positioned lateral to the UVJ area or a head located out of the neutral position is expected to increase the risk of perforation. The use of intraoperative radiographs during CPS placement will help to identify the screws that are expected to cause pedicle perforation and allow the appropriate corrections to be made.