THE RELIABILITY AND ACCURACY OF RADIOGRAPHS IN THE ASSESSMENT OF PEDICLE SCREW PLACEMENT; A COMPARISON WITH COMPUTERIZED TOMOGRAPHY

Objective: The purpose of this study was to evaluate the reliability and accuracy of radiographic assessment of pedicle screw placement, using computed tomography (CT) as the reference standard. Materials and Methods: Fifteen patients who underwent posterior spinal fusion were retrospectively reviewed. Pedicle screw position was rated using postoperative anteroposterior and lateral radiographs by two independent spinal surgeons twice at least four weeks apart. CT was rated by two other spinal surgeons collectively and reached a consensus decision. Kappa analysis was used to measure the relative agreement between radiographic ratings and CT evaluation. Results: A total of 367 screws were evaluated. According to CT evaluation, 69 (18.8%) pedicle screws were determined as malpositioned. However, in plain radiographs, 53 (14.4%) pedicle screws were rated as malpositioned. The intraobserver reliability of radiographic ratings was almost perfect for both observers at both times (ICC=0.833 and 0.817). On the other hand, the interobserver reliability was substantial at both occasions (ICC=0.722 and 0.808). The agreement between radiographic ratings and CT evaluation (reference standard) was substantial (kappa=0.686, 95% confidence interval=0.586-0.785). The sensitivity and specificity of radiographs to detect a malpositioned screw were 65.2% and 97.3%, respectively. Conclusion: Radiographic ratings showed substantial and almost perfect agreement among observers. However, the accuracy of radiography was low compared to CT evaluation. In case of suspicion, CT should be the choice of the imaging modality to decide on a malpositioned screw.