Radiographic Measurements Of Chinese Adult Transiliac Screws In Lumbopelvic Fixation

Objective:To study the feasibility and safety of the iliac screw placement, by radiographic measurements of Chinese adult iliac screw passage between posterior superior iliac spine (PSIS) and anterior inferior iliac spine (AIIS). The intercortical width at the anterior constriction of pathways above the sciatic notch were obtained as a measure for an intraosseous"safe zone"for transiliac screw insertion along an extraarticular path. Based on the findings of Berry, who showed no clinically significant age-related morphologic differences, we pooled and averaged our data by patient sex. We calculated the coefficient of biologic variation of each measurement, as a measure for interindividual morphologic variation and measurement precision within our population, as the quotient of standard deviation and mean.Material and Methods:Reconstruct 60 Chinese iliac by multilayer helicon-CT. The length of the line between PSIS and AIIS, and the distance between the line and greater sciatic notch were measured bilaterally on the lateral view, and the thickness of the cancellous and cortical bone at the two most narrow points alone the iliac screw passage bilaterally on the axial view. We performed two- and three-dimensional CT reformations of the pelvic ring using General Electric Advantage Windows software. We created two-dimensional oblique axial reformatted views along three hypothetical plane through the posterior inferior iliac spine (PIIS) and AIIS. These planes describe possible paths for transiliac screw placement with variable posterior starting points and an anterior reference point (AIIS) that would be readily identified during surgery. In all reformations, maximum length of a straight bony canal was measured in the poster anterior direction. Within each plane, the inner diameter of two stereotypic cortical constrictions were measured and located relative to the posterior starting point .Results:The length of the line between PSIS and AIIS was (140.6±1.1)mm, the cortical bone should be resected for recessing the intrailiac postssacral rod connection is (16.9±0.6)mm at male and (15.9±0.8)mm at female, and the distance between the line and greater sciatic notch was (18.3±0.8)mm, the length of the line between PSIS and the second most narrow point was (67.1±0.6) mm at male and (70.1±1.4)mm at female. The thickness of the cancellous bone was (11.0±0.7)mm at male and (9.0±0.8)mm at female at the first most narrow point, while the thickness of the cortical bone was (17.3±0.6)mm at male and (15.7±0.7) mm at female. The thickness of the cancellous bone was (11.8±0.7)mm at male and (8.1±0.7)mm at female at the second most narrow point, while the thickness of the cortical bone was (22.7±0.3)mm at male and (19.1±0.8)mm at female. From the statistic results, great variances were found in all parameters, and there were significant differences between the male and female group in all parameters except the height from sciatic to the passage and the length between PSIS and AIIS.Conclusion:There is a straight pathway in adult ilium from PSIS to AIIS. There are two most narrow points alone the pathway, which could anchor the iliac screw. The iliac screw passage could meet the sufficient demand of fixation strength with safety. Study of the preoperative CT scans facilitates operative planning and allows the instrumentation to be tailored to patients'individual iliac anatomy.