Standardized Posterior Pelvic Imaging

Abstract

Objectives The null hypothesis of the current study states that routine axial CT images are obtained at a consistent and reproducible orientation relative to the sacrum. The secondary null hypothesis states that there is no difference in the measurement of the safe zone for placement of iliosacral screws when using routine axial CT images and standardized reconstructions in defined planes perpendicular and parallel to the sacrum. Design Retrospective review. Setting University Level-1 Trauma Center Patients Sixty-eight consecutive trauma patients evaluated with routine pelvic computed tomography, without pelvic ring injury. Intervention Retrospective radiographic review and measurement. Methods Sixty-eight consecutive adult patients with routine axial pelvic CT scans, without injury to the pelvic ring and obtained as part of a trauma evaluation were retrospectively identified. The orientation of the axial slices relative to the sacrum was measured for each patient and compared. The maximal cross-sectional distance at the smallest section of the sacral ala (safe zone) was measured using the routine axial CT images and these measurements compared to similar measurements taken on standardized images perpendicular (CT Inlet) and parallel (CT Outlet) to the body of the sacrum. Additional data referencing the orientation of multiple sacral radiographic landmarks were also collected. Results The orientation of routine axial CT image planes relative to the sacrum spanned a wide range. The angle between the routine axial CT plane and the sacrum varied from 43.5 degrees to 82.0 degrees (SD = 9 degrees). Significant differences were found in measured safe zones of routine axial CT images compared to standardized CT Inlet and CT Outlet images. Compared to CT Inlet images, routine axial CT images underestimated safe zones for transverse sacral screws at both S1 (p<0.01) and S2 (p<0.01). When compared to CT Outlet images, routine axial CT images overestimated safe zones for oblique sacro-iliac screws (p<0.01), and underestimated the safe zone for S2 transverse sacral style screws (p<0.01). No significant differences in measured variables were found between genders and sacral morphology. Conclusions Our null hypotheses were rejected: routine axial CT images were found to be at widely ranging orientations relative to the sacrum, and standardized CT images (CT Inlet and CT Outlet) demonstrated statistically significant differences in measurements of safe zones compared to routine axial CT images. Furthermore, the CT Inlet and CT Outlet views provide additional information regarding sacral landmarks that could be useful for pre-operative planning.

Intra- and interrater reliabilities and a method comparison of 2D and 3D techniques in cadavers to determine sacroiliac screw loosening

“…Due to individual sacral and lumbar anatomy, the angulation for optimal visualization of pelvic anatomy in AP, inlet and outlet radiographs is variable 41–45 . This leads to a different projection of the posterior pelvic ring and individualized outlet and inlet projection angles were proposed 46,47 . However, these individualized angles are difficult to obtain in daily routine.…”

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

“…1 Percutaneous posterior pelvic ring fixation is one of the most frequently used means of fixation of the posterior ring, yet it is a technically demanding procedure. 2 The sacral morphology has a wide range of normal variations 3,4 which can make the critically important intraoperative interpretation of fluoroscopy challenging 5 ; an essential first step for a safe surgery is a careful preoperative review of a patient's specific bony anatomy to determine safe bony corridors.…”

“…Reformatting the CT scan into the inlet and outlet orientation is described. 5 This is a common practice when planning for percutaneous posterior pelvic ring fixation because it has been reported that axial nonreformatted (ANR) images provide "inconsistent safe zone measurements compared with CT inlet (axial) and outlet" (coronal) reformatted images. 5 However, the most important aspect of the preoperative review may be the identification of narrow corridors that may increase the risk of screw breach.…”

Pelvic antropometric measurement in 3D CT for placement of two unilateral iliosacral S1 - 7.3 mm screws

“…Malpositioning of percutaneous screws remains a problem and can cause iatrogenic nerve injury or revision surgery [9,10]. Flouroscopy in the emergency department includes one plain pelvic x-ray [11]. Diagnosis with this imaging is possible but not suitable for correct diagnosis and classifications or pre-operative planning.…”

“…Diagnosis with this imaging is possible but not suitable for correct diagnosis and classifications or pre-operative planning. Further x-rays as inlet-or outlet-view are possible but 3D CT scan is gold-standard for these injuries [11,12].…”