Saturday, November 2, 2001 2:14–2:57 pm Concurrent Session 6B: Lumbar Fusion Instrumentation/Monitoring: 2:14 Sensitivity and specificity of X-ray and computed tomography in assessing lumbar pedicle screw placement

Abstract

Purpose of study: The biomechanical advantage of pedicle screw fixation has improved fusion rates and diminished the number of levels required for stability. Despite the widespread clinical use of pedicle screw fixation, there is relatively little literature concerning accuracy. This study was designed to evaluate the accuracy of plain radiographs and/or computed tomography (CT) in determining the proper position of pedicle screws.Methods used: Eighteen fresh human cadaveric specimens had the lumbar spine exposed by a standard posterior approach. Titanium pedicle screws (6.5 mm) were inserted in the standard fashion. The lumbar spines were then dissected out en bloc. Anteroposterior and lateral plain films and CT scans were obtained. The posterior spinal elements and dura were then removed to examine screw location. A different examiner then reviewed the radiographs and CT to determine pedicle screw position. Screws were considered out if there was evidence of cortical perforation or if the screw was extrapedicular.of findings: The sensitivity and specificity of plain radiographs was 84.3% and 28.6%, respectively, and 89.3% and 61.9%, respectively, for CT. The combination of CT and plain radiographs increased the sensitivity and specificity to 99.3% and 100%, respectively. A nonparametric chi squared analysis failed to demonstrate any statistical difference between plain radiographs and CT (p<.05). However, statistical comparison of either CT or plain radiographs to that of both modalities showed a significant difference (p<.05). In addition, the accuracy of either CT or plain radiographs were similar. However, when imaging modalities were combined, the accuracy increased to 99%.Relationship between findings and existing knowledge: There is relatively little literature concerning accuracy of pedicle screw placement. Our study is the first to define, by means of anatomical dissection, sensitivity and specificity of plain radiograph and CT scan.Overall significance of findings: The purpose of our study was to evaluate the ability of either plain radiographs or CT to determine accurately whether a pedicle screw was properly positioned. Our findings indicate that there was no statistical difference between CT and plain radiographs. However, there was a statistically significant difference when both modalities were used together.Disclosures: No disclosures.Conflict of interest: No conflicts.