The Iliac Bone Corridor and The Angles of its Trajectory

Presented at SMISS Annual Forum 2014
By Jordan Glaser MD
With Sheeraz Qureshi MD, MBA, Hao Li BA, MS-IV,

Disclosures: Jordan Glaser MD None Sheeraz Qureshi MD, MBA A; Cervical Spine Research Society. B; Zimmer-Biomet, Stryker Spiner, Globus Medical, Inc. D; Avaz Surgical. F; RTI, Zimmer-Biomet, Stryker Spine, Hao Li BA, MS-IV None,

Introduction:
In this study we identify angular measurements on c-arm of the iliac bone corridor commonly utilized for screw placement in iliolumbar constructs and pelvic ring injuries. This corridor is identified en face utilizing the obturator outlet (“tear drop” or “teepee”) view.

Aims/Objectives:
Our goal is to contribute to current knowledge of pelvic ring anatomy by identifying specific angular measurements of the trajectory of the iliac bone corridor using fluoroscopy. To our knowledge, this study has not yet been performed and provides practical information to further understanding of pelvic structure.

Methods:
Ten cadavers were evaluated under fluoroscopy in the prone position on a radiolucent table to identify the bone corridor contained within the ilium passing between the anterior inferior iliac spine and posterior iliac spine. The obturator outlet view was then visualized under fluoroscopy starting with the right, followed by the left. The angles, obtained on the arc (rotation about the longitudinal axis) and tilt (rotation about the saggital axis), were recorded for each side using values denoted on the c-arm. Pelvic incidence was also calculated for each specimen to evaluate for correlation between trajectory of the iliac bone corridor and the anatomic relationship between the inominate bone and sacrum. Pelvic incidence was calculated off the lateral fluoroscopic view of the pelvis.

Results:
Identification of the iliac bone corridor with the specimens in the prone position was consistently identified between 25 and 35 degrees on the arc of the c-arm on all specimens. This value represents the measurement on the arc of c-arm as it was rotated off the perpendicular axis from the coronal plane of the pelvis. Tilt varied among certain specimens but was most commonly found between 15 and 25 degrees (in seven of ten specimens). Pelvic incidence measurements did not correlate with differences (increases or decreases) in angular trajectory of the iliac bone corridor among specimens.

Conclusions:
The angular trajectory of the iliac bone corridor identified on the obturator outlet view is consistent based on angular measurements obtained under fluoroscopy in this anatomic study. This trajectory differs from commonly-accepted 45 degree angular values. The angular range discussed in the results section suggests a hexagonal pelvic ring construct based on the creation of a 120 degree angle between the plane of the sacrum and the trajectory of the iliac bone corridor. Measured pelvic incidence does not seem to correlate directly with the trajectory of the iliac bone corridor.