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Patient Position: Prone
Most Likely Surgeon Position: Patient's Unaffected side
Monitor Position: Technologist side.
C-arm Position: Patient's Affected side
Expected Projections: AP, Obturator inlet view, Iliac oblique view
Obturator inlet view
The OI view is tangential to both the inner and outer cortices of the ilium at the level of the PSIS-AIIS corridor.
This view also provides an assessment of the sacroiliac joint and is used to guide the medial lateral trajectory
.A: Obturator inlet view. C-Arm relative to the patient.
B: Obturator inlet view demonstrating visualization of the outer iliac cortex (thin black arrows), medial border (thin white arrows), sacroiliac joint (white arrowheads), hip joint (black arrowheads), posterior sacral ala (large black arrow) and PSIS (large white arrow).
Photos demonstrating the c-arm position for the obturator inlet view relative to the pelvis in the prone position (C) and (D).
Procedure for achieving Obturator inlet view
C-arm is first positioned for the AP view (A) and (B)
Then the c-arm is tilted caudally (C) until the anterior S1 and S2 vertebral bodies overlap as demonstrated by a crisp anterior vertebral cortex (white arrows) is visualized (D).
Then the c-arm position is rotated away from the affected side (E) until the the outer table of the PSIS is well delineated as demonstrated by a crisp outer iliac cortex (black arrows) (F).
Obturator Inlect View: Optimal (A) , Not enough tilt (B) , Too much tilt (C)
Fluoroscopic obturator inlet view demonstrating a crisp outer cortical line (black arrows) (A).
This is obscured if there is too little (B) or too much (C) obturator tilt.
Iliac Oblique view
This view is used to guide the cranial-caudal trajectory.
A: C-arm relative to the patient
B: Inlet oblique view demonstrating visualization of the sciatic notch (black arrows), AIIS (dashed white line), PSIS (white arrowheads), and hip joint (black arrowheads).
Photos demonstrating the c-arm position for the iliac oblique view relative to the pelvis in the prone position (C) and (D).
Procedure for achieving Iliac Oblique view
C-arm is first positioned for the AP view (A) and (B)
Roll back towards the affected side of the hemiplevis until the sciatic notch and the anterior inferior iliac spine can be clearly delineated.
Obturator inlet view. Cannulation instrument aiming too lateral (A), too medial (B), and with a cannulation instrument safely down the sciatic buttress corridor(C).
Iliac oblique view with cannulation instrument aiming too caudal (D) and too cranial (E) relative to the AIIS (white dashed line). (F) The cannulation Instrument shown was directed safely down the sciatic buttress corridor toward the AIIS.
El Naga, A. N., & Gendelberg, D. (2024). Obturator inlet and iliac oblique technique for safe, convenient, and reliable iliac screw placement. North American Spine Society Journal (NASSJ), 17, 100298. https://doi.org/10.1016/j.xnsj.2023.100298
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