Reliability of Postoperative Multi-slice Computed Tomography in Assessment of Pedicle Screw Placement in Thoracic and Lumbar Spinal Fixation

Transpedicular instrumentation procedure has become an established method for stabilization of the thoracic and lumbar spines. Since their introduction, the accuracy and complication of placing pedicle screws has been the subject of many reported studies. Objective: To evaluate the reliability of three-dimensional (3-D) volume rendering computed tomography (CT), in postoperative assessment of pedicle screw placement. Patients and Methods: Ninty eight patients with previous spinal fixation surgery were included. All inserted screws were evaluated post operatively within the first week using CT. Degree of misplacement and difference between CT images were recorded. Results: 76, 68 and 39 misplaced screws were detected in 3-D reformatted image, coronal reconstruction and axial CT images respectively. Dorsal spine had higher rate of violation 46 (9.95%) with the highest rate at T4 (12.8 %) comparing it with lumber 32 (6.9 %). Statistically significant differences were found between lateral and medial violation (P value=0.03), between findings of CT-3D reformatted and axial image (P = 0.04), and also in detecting end plate perforation and anterior vertebral encroachment in different CT images (P value=0.013). Sensitivity for 3-D reformatted image and axial image compared with surgical finding in six revised screws was 100% and 95.8 % and specificity 100% and 88.7% respectively. Highly momentous agreement reported with Kappa coefficient=0.95 ± 0.001. Conclusion: The vertebral body and the pedicle are 3-D structures. Therefore, we have to study them as they are. The postoperative evaluation of pedicle screw using CT-3D reconstruction was a reliable method and unveiled the deficiencies in conventional axial CT.