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 perpendicular to the IR, vertical into the table Bucky, centered 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. A sample technique is 96 kVp with DR 45 or CR 100 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Entire sacrum from base to apex.
- L5 vertebra and lumbosacral junction.
- Sacral curvature (convex posterior surface, concave anterior surface).
- Anterior sacral margin.
- Sacral canal in lateral profile.
- 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
Perpendicular to the IR, vertical into the table Bucky, centered 3-4 inches posterior to the ASIS.
Exposure / technique
- kVp
- 96
- mAs
- DR 45 / CR 100
- SID
- 40" (102 cm)
- Notes
- Higher mAs needed due to thick pelvic anatomy. kVp: Bontrager lists 90 +/- 5 kV digital; Merrill's chart prints 96. High amounts of scatter are generated: use close collimation and lead masking behind the patient. From March 1, 2027, the ARRT outline lists only the combined lateral sacrum and coccyx. Sample technique: DR 45 / CR 100 mAs at 96 kVp, 40 in SID, for a 31 cm part (Merrill's sample chart). Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Mid-sagittal plane parallel to IR (no rotation).
- L5 and sacral base clearly demonstrated.
- Bony margins and trabecular markings of the sacrum clear, with no motion.
- Anterior margin of sacrum delineated.
- Greater sciatic notches and femoral heads superimposed (no rotation).
Common errors
- 1 Patient rotation: the greater sciatic notches and femoral heads are not superimposed.
- 2 CR not centered to the sacrum (3-4 inches posterior to the ASIS) results in anatomy off-axis.
- 3 Excessive kVp reduces bone detail due to scatter.
Clinical indications
- Pathology of the sacrum and coccyx, including fracture.
- Sacral fracture, tumour, or bony destruction assessment.