A comparative study of CT reconstruction for preoperative evaluation of safe C2 pedicle screws placement

English Keywords:C2 pedicle screw  Pediculoisthmic component  High-riding vertebral artery  CT reconstruction  Preoperative evaluation

English Abstract:

  【Abstract】 Objectives: To evaluate the feasibility of safe placement of C2 pedicle screws by measuring the morphometric diameters on the narrowest portion of C2 pediculoisthmic component(PIC) with CT angiography multiplanar reconstruction(CTA MPR), and to compare with the two commonly used clinical methods of axial CT(CT AXIS) and the definition of high-riding vertebral artery(HRVA) to assess their false positive rates and false negative rates. Methods: Consecutive patients who had undergone CT examination and head and neck CT angiography(CTA) scan were included. The width of the endosteal cavity(a1) and outer diameter(a2) of C2 bilateral pedicles were measured by means of CT AXIS. The isthmus height(b) and internal height(c) were measured on an orthogonal sagittal CT image at 3mm lateral to the cortical margin of the spinal canal wall at C2, and HRVA was defined. The width of the endosteal cavity(d1), width of the outer diameter(d2), the height of the endosteal cavity (e1) and height of the outer diameter (e2) were measured by means of CTA MPR at the narrowest section of C2 PIC. Disparities of the morphometric parameters between CT AXIS method and CTA MPR method were compared. Unfeasible proportions of C2 pedicle screw placement evaluated by all the three methods were calculated, and the false positive rates and false negative rates of CT AXIS method and HRVA definition were analyzed based on CTA MPR method as the "gold standard". Results: A total of 304 C2 PICs of 152 patients were measured with CTA MPR and CT AXIS methods separately, the endosteal diameter(3.82±1.58mm vs 2.55±1.16mm) and outer diameter(6.54±1.91mm vs 5.48±1.49mm) each were with statistical differences between the two methods(P<0.001). Besides, with the CTA MPR method, the height measured was significantly bigger than the width(endosteal: 6.55±1.34mm vs 3.82±1.58mm; outer: 10.2±1.22mm vs 6.54±1.91mm) (P<0.001). Regarding CTA MPR method as the "gold standard", the false negative rate and false positive rate of CT AXIS method were 6.91% and 20.69%, respectively; the false negative rate and false positive rate of HRVA definition were 11.64% and 3.45%, respectively. There were significant differences between CTA MPR method and the methods of CT AXIS and HRVA definition in evaluating the placement feasibility of pedicle screws(P<0.01). Conclusions: CTA MPR measurement is able to simulate C2 pedicle screw path and measure the morphometric parameters at the narrowest section of C2 PIC accurately, which is a precise method in evaluating the feasibility of safe placement of C2 pedicle screw preoperatively. Whereas, the evaluation methods of CT AXIS and HRVA definition have partly false positive rate and false negative rate that may lead to misjudgment or omission of the feasibility of C2 pedicle screw placement, increasing the risk of vertebral artery injury or choosing biomechanically deficient C2 screw placement.