IMAGING ASSESSMENT OF SACROILIAC SCREW PLACEMENT RELATIVE TO THE NEUROFORAMEN

Study Design. Twenty-four cannulated sacroiliac screws were placed bil aterally into 12 cadaveric pelvi (12 titanium screws and 12 stainless- steel screws) and were imaged using conventional and multiplanar recon structed computed tomography. Objectives. To determine whether sacroil iac screw position assessment relative to the neuroforamen is enhanced by: 1) computed tomography using multiplanar reconstructions and 2) t he use of titanium screws rather than stainless-steel screws. Summary of Background Data. To the authors' knowledge, there have been no prio r studies demonstrating the accuracy of multiplanar computed tomograph y compared with that of conventional (axial) tomography in determining the position of sacroiliac screws relative to the neuroforamen. Altho ugh titanium screws have been shown to have less scatter than stainles s-steel screws, the effect of alloy composition on the radiographic ac curacy of interpreting the screw position relative to the sacral neuro foramen is unknown. Methods, Screws were deliberately placed into: pos ition 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 neurofor amen; and position C, in which the screw clearly was nearly centered i n the neuroforamen. The degrees of accuracy in assessing screw positio n relative to the neuroforamen using conventional (axial) images and u sing multiplanar reconstructed images were compared. Results. The axia l images were accurate in determining screw position relative to the n euroforamen in 50% of cases in which titanium screws were used and in 42% of cases in which stainless-steel screws were used. The correspond ing 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 stat istically better than that of axial images (P < 0.05). Metallic scatte r was increased in stainless-steel screws. Conclusion. The results of this study suggest that the use of computed tomography with multiplana r reconstruction improves accuracy in determining sacroiliac screw pos ition relative to the neuroforamen. The assessment of screw position m ay be facilitated using titanium screws.