SI Joints Posterior Oblique (RPO/LPO)
Position the Patient
- Supine
- Rotate patient 25-30° away from the side of interest
- Side of interest elevated
- Pelvis aligned without tilt
Words That Work
“Lie on your back with your legs straight. I’ll roll your shoulders and hips together about 25 to 30 degrees—like rolling a log—and support you in that position. This angle opens the sacroiliac joint we need to see. Breathe all the way out, hold it, and don’t let your body roll.”
Posterior oblique SI joints positioning
Set Up the Shot
- Center here
- Central ray
- 1" medial to ASIS on elevated side
- Include this in the field
- Collimation
- SI joint region
- Set the distance
- SID
- 40"
- Check the technique
- Technique
- 75-85 kVp
- Follow facility protocols
Common Pitfalls
- •Incorrect rotation angle (not 25-30°)
- •SI joint not clearly open
- •Motion
Evaluate the Image
What should be visible?
- SI joint of elevated side (RPO shows the left joint; LPO shows the right)
- Sacroiliac articulation (SI joint farthest from the plate is demonstrated)
Does the image pass?
- ✓SI joint clearly open
- ✓Correct 25–30° rotation
- ✓No motion