Comparison of cortical and cancellous screw pull-out strengths about the posterior column and sacroiliac joint

This study addresses the comparative pull-out strengths of cortical (4.5 mm) and fully threaded cancellous (6.5 mm) bone screws from sites about the pelvis commonly used in the fixation of posterior column acetabular fractures and sacroiliac (SI) disruptions. These sites include one from lateral to medial through the posterior column, two from posterolateral to anteromedial across the SI joint, one vertically through the sacral ala, and one vertically through the iliopubic column (see Fig. 1A and B). Statistical analysis showed no significant difference in the force required for pull-out failure of the cortical versus the cancellous screws at any of the sites tested.