Sacrum Lateral is a radiography positioning projection of the Pelvis. True lateral sacrum. SID 40". CR perpendicular to IR. The centering point is located at the level of the asis, approximately 3-4 inches posterior to the asis. mid-sagittal plane parallel to ir.. The central ray is horizontal, perpendicular to ir. centered to the sacrum, 3-4 inches posterior to the asis.. Image-quality criteria include mid-sagittal plane parallel to ir (no rotation)., l5 and sacral base clearly demonstrated.. Standard exposure ranges from 85 to 95 kVp, 40 to 80 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Entire sacrum from base to apex.
- L5 vertebra and lumbosacral junction.
- Sacral curvature (normal concavity).
- Anterior sacral margin.
- Sacroiliac joint articulation.
- Coccyx in relation to sacrum.
Patient preparation
- Verify patient identity.
- Position patient in left or right lateral position.
- Align mid-sagittal plane parallel to IR.
- Flex hips and knees slightly for stability.
- Place radiolucent support under waist to prevent sag.
- Remove radiopaque objects from pelvis and lumbar spine.
- Suspend respiration during exposure.
Position & centering point
At the level of the ASIS, approximately 3-4 inches posterior to the ASIS. Mid-sagittal plane parallel to IR.
Central ray
Horizontal, perpendicular to IR. Centered to the sacrum, 3-4 inches posterior to the ASIS.
Exposure / technique
- kVp
- 85–95
- mAs
- 40–80
- SID
- 40" (102 cm)
- Notes
- Higher mAs needed due to thick pelvic anatomy. Moderate kVp for adequate penetration without excessive scatter.
Image-quality criteria
- Mid-sagittal plane parallel to IR (no rotation).
- L5 and sacral base clearly demonstrated.
- Sacral curvature shown without distortion.
- Anterior margin of sacrum delineated.
- Sacroiliac articulation visible.
- Superimposed ischial tuberosities (no rotation).
Common errors / ARRT traps
- 1 Patient rotation causes sacral foramina or ala visibility.
- 2 Insufficient IR allows cutoff of sacral apex.
- 3 CR not centered to L5-S1 results in anatomy off-axis.
- 4 Forward pelvic tilt obscures sacral curvature.
- 5 Excessive kVp reduces bone detail due to scatter.
Clinical indications
- Suspected sacral fracture with lateral displacement.
- Evaluation of sacral curvature and angulation.
- Assessment of lumbosacral junction stenosis.
- Postsurgical sacral fusion alignment verification.
- Sacroiliitis or SI joint pathology assessment.
Aligned to the 2025 ARRT Content Specifications.