Defining Sacral Dysmorphism: What Size Corridor Precludes Transsacral Screw Placement.

OBJECTIVE: To determine what size S1-transsacral (TS) corridor is amenable to TS screw placement, as this is commonly used to identify sacral dysmorphism, and to determine if gender, ethnicity, or screw breach is associated with narrow corridors. DESIGN: Retrospective review. SETTING: Urban level-1 trauma center. PATIENTS: Two hundred ninety patients with pelvic ring injuries and preoperative computed tomography (CT) scans. INTERVENTION: Percutaneous posterior pelvic ring fixation. MAIN OUTCOME MEASUREMENTS: The width of the S1-TS corridor was measured on the axial (inlet) and coronal (outlet) reformatted CT images. Patients with S1-TS screw fixation and postoperative CT scans were identified. Corridor size, gender, ethnicity, and screw breach were documented. RESULTS: S1-TS screws were placed in 55 of the 290 patients. No S1-TS screws were placed in corridors less than 8 mm. Corridors of <8 mm were present in 114 (39%) of the 290 patients and were not associated with gender or ethnicity. S1-TS screws placed in small (<10 mm) versus large (≥10 mm) corridors did not have a detectable difference in screw breaches (5 of 8, 62% versus 19 of 47 40%; difference, 22%, 95% confidence interval -14% to 52%) or median (interquartile range) screw breach distance [3 mm (2.5-4.8) versus 3 mm (1.2-4.8); difference, 0.9 mm; confidence interval -1.6 to 2.2]. CONCLUSION: These data are useful for the standardization of sacral dysmorphism reporting based on corridor size. Screw breaches were common irrespective of TS corridor size, emphasizing the small degree of error allowed by this procedure. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Using Reformatted Axial Computed Tomography Images in Isolation Will Miss Narrow S1 Transsacral Screw Corridors.

OBJECTIVE: To evaluate S1 transsacral (TS) corridors on reformatted and nonreformatted computed tomography (CT) images to determine which most reliably identifies narrow corridors. DESIGN: Retrospective cohort. SETTING: Level 1 trauma center. PATIENTS: Two hundred forty-five patients with operative pelvic ring injuries. INTERVENTION: CT scan review. MAIN OUTCOME MEASUREMENTS: Preoperative CT scans were evaluated to determine the width of the S1 TS corridor on standard axial nonreformatted (ANR), axial reformatted (AR), and coronal reformatted images. Sensitivity and specificity of each format to detect a narrow corridor (<10 mm on AR or coronal reformatted) were calculated. Patients with S1 TS screws were evaluated to determine the rate of screw breach with narrow corridors. RESULTS: The axial width of the S1 TS corridor was consistently smaller on ANR versus AR images (mean difference 1.4mm, 95% confidence interval 1.1-1.5). The corridor width on ANR images was on average 86% of the AR measurement. ANR images had the highest sensitivity and specificity (100% and 98%) for detecting S1 TS corridors <10 mm. Fifty-three S1 TS screws were placed in corridors ranging 10-23 mm on AR images and 7-19 mm on ANR images. Four (57%) of the 7 screws placed in corridors less than 10 mm in width on ANR images breached the sacral cortex. CONCLUSION: Using ANR images to measure the S1 TS corridor consistently measured smaller widths than AR images and identified all narrow corridors. A high rate of screw breach was noted with screw placement in narrow corridors. LEVEL OF EVIDENCE: Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.