Imaging assessment of sacroiliac screw placement relative to the neuroforamen

Study Design. Twenty-four cannulated sacroiliac screws were placed bilaterally into 12 cadaveric pelvi (12 titanium screws and 12 stainless- steel screws) and were imaged using conventional and multiplanar reconstructed computed tomography. Objectives. To determine whether sacroiliac screw position assessment relative to the neuroforamen is enhanced by: 1) computed tomography using multiplanar reconstructions and 2) the use of titanium screws rather than stainless-steel screws. Summary of Background Data. To the authors knowledge there have been no prior studies demonstrating the accuracy of multiplanar computed tomography compared with that of conventional (axial) tomography in determining the position of sacroiliac screws relative to the neuroforamen. Although titanium screws have been shown up to have less scatter than stainless-steel screws the effect of alloy composition on the radiographic accuracy of interpreting the screw position relative to the sacral neuroforamen is unknown. Methods. Screws were deliberately placed into position A, in which the screw did not violate the neuroforamen, position B, in which the threads of the screw came within 3 mm of the neuroforamen, and position C, in which the screw clearly was nearly centered in the neuroforamen. The degrees of accuracy in assessing screw position relative to the neuroforamen using conventional (axial) images and using multiplanar reconstructed images were compared. Results. The axial images were accurate in determining screw position relative to the neuroforamen in 50% of case in which titanium screws were use and in 42% of cases, in which stainless-steel screws were used. The corresponding values for multiplanar reconstructions, were 92% for cases in which titanium screws were used and 67% for cases in which stainless-steel screws were used. The accuracy of multiplanar reconstructions was statistically better than that of axial images (P < 0.05). Metallic scatter was increased in stainless-steel screws. Conclusion. The results of this study suggest that the use of computed tomography with multiplanar reconstruction improves-accuracy in determining sacroiliac screw position relative to the neuroforamen. The assessment of screw position may be facilitated using titanium screws.