Intra-operative fluoroscopy for detecting pedicle screw violation in lumbar vertebrae by guided pin axial position

Objectives To develop an applicable and accurate intra-operative fluoroscopical angle to observe the placement of pedicle screw and pedicle violation. Methods Lateral radiographs were taken on eighty lumbar pedicles in eight cadaveric vertebral specimens to measure the sagittal pedicle angles. The pedicles of the vertebral arch were scanned by computed tomography (CT) to measure the transverse pedicle angles. Guided pins and pedicle screws were inserted by awl into the pedicles through the holes drilled in the lumbar pedicles so as to establish 3 types of model: medial violation (n=29), lateral violation (n=25), and properly placed screw (n=26) the anterior and posterior portions of the lumbar pedicle cortex could be identified by the fluoroscopy C-arm. Fluoroscopy with the aid of C-arm was taken on each pedicle in five different directions: lateral position; anteroposterior position; pedicle axial position; guided pin axial position; and pedicle screw axial position. The positions of guided pin and pedicle screw were evaluated. The gold standard was acquired by excising the vertebral plate and observing directly. Results Nine cases of medial violation were discovered and the accuracy rate was 33.75% by anteroposterior fluoroscopy. The accuracy rate was 95% by the pedicle axial fluoroscopes, including 4 cases of medial inclination but properly placed screws were mistaken for medial violation by pedicle axial fluoroscope. The accuracy rate was 100% by guided pin axial position fluoroscopy, including 29 cases of medial violations, 25 cases of lateral violation, and 26 cases of properly placed screws. Conclusion The approach of intra-operative fluoroscopy of guided pin axial position is a reliable technology for detecting pedicle violation with the aid of C-arm. The incidence of flexible pedicle screw from human factors can be reduced.