Coccyx Lateral is a radiography positioning projection of the Pelvis. True lateral coccyx. SID 40". CR perpendicular to IR. The centering point is located at the level of coccyx, approximately 1.5 inches posterior to pubic symphysis on midline.. The central ray is horizontal, perpendicular to ir. centered to the coccyx.. Image-quality criteria include coccyx shown without rotation or forward angulation., all coccygeal segments visible.. Standard exposure ranges from 80 to 90 kVp, 25 to 50 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- All coccygeal segments and their alignments.
- Articulation between coccyx and sacral apex.
- Coccygeal curvature and angulation.
- Anterior surface of coccyx.
- Relationship to ischial tuberosities.
Patient preparation
- Verify patient identity.
- Position patient in left or right lateral position.
- Align mid-sagittal plane parallel to IR.
- Flex hips and knees for patient comfort and stability.
- Place pillow or support under waist to prevent rotation.
- Remove radiopaque objects from perineal area.
- Suspend respiration during exposure.
Position & centering point
At the level of coccyx, approximately 1.5 inches posterior to pubic symphysis on midline.
Central ray
Horizontal, perpendicular to IR. Centered to the coccyx.
Exposure / technique
- kVp
- 80–90
- mAs
- 25–50
- SID
- 40" (102 cm)
- Notes
- Slightly lower mAs than sacral lateral due to thinner anatomy. Moderate kVp for good penetration.
Image-quality criteria
- Coccyx shown without rotation or forward angulation.
- All coccygeal segments visible.
- Articulation between coccyx and sacral apex clear.
- Anterior margin of coccyx delineated.
- Coccyx centered on IR.
- No superimposition of proximal femur.
Common errors / ARRT traps
- 1 Patient rotation causes ischial tuberosity superimposition.
- 2 Forward pelvic tilt overlaps proximal femur on coccyx.
- 3 CR not centered to coccyx results in off-axis anatomy.
- 4 Insufficient IR size causes coccygeal apex cutoff.
- 5 Excessive kVp obscures coccygeal segment detail.
Clinical indications
- Suspected coccygeal fracture.
- Coccydynia evaluation for anatomic cause.
- Assessment of coccygeal angulation or curvature.
- Post-traumatic coccygeal alignment check.
Aligned to the 2025 ARRT Content Specifications.