Sacroiliac joint (PA oblique view)
The PA oblique view of the sacroiliac joints can be performed in patients who cannot assume the supine position. Both sides of the sacroiliac joints are examined for comparison. Oblique views can be taken either AP or PA.
- patient positioned semi-prone with a flexed knee can usually support for this position
- the side being examined is closer to the image receptor, 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 25-30°
- posteroanterior oblique projection
- perpendicular to the image receptor, centring 1 cm medial to the posterior inferior iliac spine closest to the image receptor.
- laterally to include the entire sacroiliac joint of interest
- superiorly and inferiorly to include the entire joint
- 18 cm x 24 cm
- 75 kVp
- 25-30 mAs
- 100 cm
Image technical evaluation
- the sacroiliac joint closest to the image receptor should be shown open or with minimal superimposition of the ilium and the sacrum
- joint is centered on the radiograph
- the degree of obliquity required to show the sacroiliac joint in a PA oblique position is usually shallow (25-30°)
a radiolucent support such as a sponge can be used to help elevate the hip and thorax to maintain position
- a 20-25° caudal angle, centered to posterior inferior iliac spine will project the central ray perpendicular to the long axis of the sacroiliac joint.