Computer-assisted Evaluation of Pedicle Screw Position on CT Images

Yeom, Jin Sup; Chung, Moon Sang; Lee, Choon Ki; Chang, Bong Soon; Kim, Yeongho; Kim, Namkug; Lee, Jae Bum

Abstract

PURPOSE
The purpose of this study was to develop a personal computer-based method to facilitate the evaluation of pedicle screw position on computed tomography (CT) scan images and to assess its diagnostic value. MATERIAL AND METHOD: A personal computer-based method was developed using the CT images of 17 patients having a total of 84 pedicle screws. Images with a window range of -2, 000 to +3, 000 were inverted; a multiplanar reconstruction viewer was then produced to create these images in the sagittal and coronal planes. Finally, lines circumscribing the threaded portion of screws were drawn on the images. For CT images of thirty-two pedicle screws placed in the lumbar vertebrae of four pigs, screw locations were evaluated by 6 orthopaedic surgeons by our method and by conventional bone window setting. The diagnostic values of the two methods were calculated and compared. RESULT: Our method significantly improved the specificity (from 82% to 94%, p=0.007), the positive predictive value (from 79% to 92%, p=0.015), and inter-observer agreement (from 0.61 to 0.78, p<0.001) in terms of identifying misplaced screws. CONCLUSION: The described method improves the diagnostic accuracy and inter-observer reliability for the identification of misplaced pedicle screws on CT scan images.