Comparison Of Computerized Tomography And Direct Visualization On Thoracic Pedicle Screw Placement

Transpedicular screw fixation is used widely in spine surgery, especially in orthopedic surgery. We have been accustomed to see computerized tomography (CT) scanning as a "golden standard" to assess the accuracy of thoracic pedicle screw placement clinically and experimentally. But the phenomenon of plastic deformation of bone, the metal artifact and Bulk-forming effect influence the accuracy of CT. One of the indications of neural complications is the medial cortical perforation. To be a orthopedic doctor , how to estimate accurately whether the pedicle screw penetrate the medial wall is very important. However, there isn't a paper for studying the sensitivity, specificity and the degree of agreement of CT in assessing the by now. Objectives: To validate computerized tomography (CT) scanning as a tool to assess the accuracy of thoracic pedicle screw placement and find ways to improve the sensitivity, specificity and the degree of agreement of CT。Materal and methods: In part 1 of the study, Five fresh human cadaveric spines (T1-12) were harvested. Speciments with frature and tumors were excluded from the study. The speciments will be dip in saline for two days. Before inserting the pedicle screw into the spine ,we scanned the speciments firstly, according to which we can select the diameter of pedicle screw and which is helpful to our assessment for the the accuracy of thoracic pedicle screw placement. A grading scale was devised to score the placement of the pedicle screw. The grades ranged from 0 to 2 depending on the extent to which the pedicle medial wall had been violated. One hundred twenty pedicles were fitted with instrumentation in five cadaveric spines. three observer graded the appearance of the screw based on CT scans (3-mm axial sections with 1-mm overlap) and direct visualization of the specimen. In part 2 of the study, we deal with the CT image of throracic pedicle screw with three different ways to find a method that can improve the sensitivity, specificity and the degree of agreement of CT Results The authors arrived at a Kappa value of 0.603, which suggested only moderate agreement between the two measurement techniques. For pedicle screw of gradeⅠ, CT had a positive predictive value of 32%, a negative predictive value of 88%.,a sensitivity of 33% and a specificity of 87%. Whereas , for pedicle screw of gradeⅡ, CT had a positive predictive value of 60%, a negative predictive value of 100%.,a sensitivity of 100% and a specificity of 88%. When we do the CT image with "bone widow",for pedicle screw of gradeⅠ,CT had a positive predictive value of 0%, a negative predictive value of 82%.,a sensitivity of0% and a specificity of 82%; for pedicle screw of gradeⅡ, CT had a positive predictive value of 75%, a negative predictive value of 100%.,a sensitivity of 100% and a specificity of 82%. The Kappa value is 0.452.After dealing with the CT image of pedicle screw with interpolation numberical method, for pedicle screw of gradeⅠ,CT had a positive predictive value of 52.7%, a negative predictive value of 94%.,a sensitivity of 67% and a specificity of 94%; for pedicle screw of gradeⅡ, CT had a positive predictive value of 75%, a negative predictive value of 100%.,a sensitivity of 100% and a specificity of 94%. The Kappa value is 0.725.Conclutions:The authors thus conclude that although CT scanning is the most valid tool to assess the accuracy of thoracic pedicle screw placement, it tends to overestimate the number of misplaced screws. The ways of "high window width and low window level" , interpolation numberical method and individualized location of pedicle before CT scanning will improve the the sensitivity, specificity and the degree of agreement of CT .