Use of fluoroscopy to evaluate iliac screw position

Iliac screw fixation is often used for long fusions to the sacropelvis. Maximum iliac screw purchase is obtained both by placing the screws within 1.5 cm of the greater sciatic notch and by extending them anterior to the axis of rotation in flexion-extension. Screw insertion is "blinded" or dependent on tactile feedback, and hence extreme care is necessary to avoid incorrect placement and damage to vital neurovascular structures in the pelvis and sciatic notch. Long screws may violate the hip joint while medial placement may injure the lumbosacral plexus and the nearby vessels. To explore the best intraoperative fluoroscopic method of determining optimal iliac screw placement, we used a synthetic pelvis model to investigate screw placement conditions: (1) optimal anatomic placement, (2) violation of the sciatic notch, (3) hip joint violation, (4) medial wall violation, and (5) lateral wall violation. Each condition was examined utilizing fluoroscopy with posteroanterior, inlet, outlet, lateral, iliac oblique, and obturator oblique Judet views to simulate operative conditions. These views were obtained to evaluate critical malposition of iliac screws. We found that, for a sciatic notch violation, the obturator oblique view best demonstrated the cortical breech, while for a hip joint violation, the inlet and outlet views were best. For a medial wall violation, the iliac oblique view best showed the violation. For a lateral wall violation, we were unable to demonstrate the cortical breech using these fluoroscopic views. Fluoroscopy is an effective method to determine sciatic notch, hip joint, and medial wall violations after iliac screw placement; however, it is not effective in identifying a lateral wall violation.