Revision 3 for 'Sacroiliac joint (PA oblique view)'

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Sacroiliac joints: PA Oblique view

Oblique views can be taken either AP or PA. The PA oblique view of the sacroiliac joints can be performed in patients who cannot assume the supine position. Both sides of the SIJs are examined for comparison.

 

Patient position

·         Patient positioned semi-prone with a flexed knee can usually support for this position

·         The side being examined is closer to the IR

·         Therefore use the RAO position to demonstrate the right joint space and the LAO position to demonstrate the left joint space

·         The degree of obliquity is approximately 25-30degrees

 

Technical factors

·        PA Oblique projection

·        centring point

o   Perpendicular to the IR, centring 1cm medial to the PSIS closest to the IR

·        collimation

o   laterally to include the entire sacroiliac joint of interest

o   superiorly and inferiorly to include the entire joint

·        orientation  

o   portrait

·        detector size

o   18 cm x 24 cm

·        exposure

o   75 kVp

o   25-30 mAs

·        SID

o   100 cm

·        grid

o   yes

                                                                    

 

Image technical evaluation

·         The sacroiliac joint closest to the IR should be shown open or with minimal superimposition of the ilium and the sacrum

·         Joint is centered on the radiograph

 

Practical points

·         The degree of obliquity required to show the SIJ in an PA oblique position is usually shallow (25-30deg)

·         A radiolucent support such as a sponge can be used to help elevate the hip and thorax to maintain position

A 20-25 degree caudal angle, centered to PSIS will project the central ray perpendicular to the long axis of the Sacro-iliac joint.

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