Coccyx AP Axial is a radiography positioning projection of the Pelvis. Axial view of coccyx. CR 10° caudad. SID 40". The centering point is located approximately 2 inches superior to the pubic symphysis, on the midline.. The central ray is 10° caudad to the long axis of the coccyx, entering 2 inches superior to the pubic symphysis.. Image-quality criteria include coccygeal segments shown without superimposition., articulation between coccyx and sacral apex visible.. Standard exposure ranges from 70 to 80 kVp, 15 to 25 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- All coccygeal segments (typically 4 fused segments).
- Articulation between coccyx and sacral apex.
- Coccygeal curves and angulation.
- Relationship to pubic symphysis.
- Soft tissue outline of coccyx and perineum.
Patient preparation
- Verify patient identity.
- Position patient supine on the table.
- Remove radiopaque objects from perineal area.
- Flex hips and knees to relax pelvic floor musculature.
- Explain procedure; patient may experience mild discomfort.
- Suspend respiration during exposure.
Position & centering point
Approximately 2 inches superior to the pubic symphysis, on the midline.
Central ray
10° caudad to the long axis of the coccyx, entering 2 inches superior to the pubic symphysis.
Exposure / technique
- kVp
- 70–80
- mAs
- 15–25
- SID
- 40" (102 cm)
- Notes
- Lower kVp than sacrum due to thinner anatomy. Smaller focal spot helps delineate coccygeal segments.
Image-quality criteria
- Coccygeal segments shown without superimposition.
- Articulation between coccyx and sacral apex visible.
- No rotation of coccyx; segments aligned.
- Coccyx centered on IR.
- Soft tissue outline of coccyx visible.
- Minimal pubic symphysis superimposition.
Common errors / ARRT traps
- 1 CR angle insufficient results in foreshortened coccyx segments.
- 2 Patient rotation causes off-midline positioning.
- 3 Insufficient IR collimation includes excess pelvic anatomy.
- 4 Pubic symphysis shadows coccygeal base.
- 5 CR not centered to midline causes lateral cutoff.
Clinical indications
- Suspected coccygeal fracture from trauma or fall.
- Coccydynia (tailbone pain) evaluation.
- Post-traumatic coccygeal alignment assessment.
- Presurgical planning for coccygeal manipulation or removal.
Aligned to the 2025 ARRT Content Specifications.