Radiographic assessment of sacral screw placement.

Sacral screw penetration of the anterior sacral cortex runs the risk of injury to neural, vascular, and visceral structures. This study examined the accuracy of the standard anteroposterior (AP) and lateral roentgenographic views as compared to a modified pelvic inlet (MPI) view in determining sacral screw penetration and angulation. Ten human cadaveric specimens were studied. Screw depth and screw angulation in the transverse plane were best evaluated with the MPI view. Screw penetration was overestimated by 0.4 mm (+/- 2.2 mm) on the MPI view, whereas the lateral view overestimated screw penetration by 2.8 mm (+/- 4.7 mm). Screw angulation in the sagittal plane could only be evaluated by the lateral view. The standard anteroposterior view provided little useful information on sacral screw orientation. To study all parameters of sacral screw placement, the radiographic series should include a modified pelvic inlet view and a lateral sacral view.