The accuracy of computer-assisted percutaneous iliosacral screw placement

The benchmark fluoroscopic technique of iliosacral screw insertion is disadvantaged by its reliance on ionizing radiation and presentation of dynamic information in only one plane. Multiplane targeting requires interpolation, which may be associated with inherent errors. Computer-assisted surgery enables surgeons to monitor their screw trajectory in 3-D space. The clinical application of computer-assisted surgery requires validation of its accuracy when tested against a benchmark technique. We simulated surgical implantation of cannulated screws in 10 embalmed human cadavers. Two specimens had sacral dysplasia. We inserted 20 screws into the S1 body, the left side by the benchmark fluoroscopic technique and the right side by a fluoroscopically registered computer-assisted surgery technique. All specimens were intact with no simulated injuries. A postoperative high-definition computed tomography scan showed the screw track. The actual track was compared with the intended screw track by a graphical technique. There was no deviation from the intended screw path in any of the simulated screw paths. With both techniques, two of the 10 tracks penetrated the sacral cortex in dysplastic pelvices. A fluoroscopic computer-assisted surgery technique appears as accurate as the standard fluoroscopic technique but no more so. Caution is recommended in dysplastic pelvices.