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, entering 2 inches superior to the pubic symphysis. Image-quality criteria include coccygeal segments shown without superimposition, coccygeal segments appear open. A sample technique is 85 kVp with DR 14 or CR 32 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- All coccygeal segments (three to five fused in the adult, average four).
- Articulation between coccyx and sacral apex.
- Relationship to pubic symphysis.
Patient preparation
- Verify patient identity.
- Position patient supine on the table.
- Remove radiopaque objects from perineal area.
- Keep the legs extended, with support under the knees for comfort.
- Have the patient empty the urinary bladder before the procedure.
- Suspend respiration during exposure.
Position & centering point
Approximately 2 inches superior to the pubic symphysis, on the midline.
Central ray
10° caudad, entering 2 inches superior to the pubic symphysis.
Exposure / technique
- kVp
- 85
- mAs
- DR 14 / CR 32
- SID
- 40" (102 cm)
- Notes
- Bontrager lists a lower digital range than for the sacrum: 80 +/- 5 kV. CR may need 15 degrees caudad with greater anterior curvature. Sample technique: DR 14 / CR 32 mAs at 85 kVp, 40 in SID, for a 17 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
- Coccygeal segments shown without superimposition.
- Coccygeal segments appear open.
- No rotation of coccyx; segments aligned.
- Coccyx centered on IR.
- Bony margins and trabecular markings of the coccyx clear, with no motion.
- Coccyx projected superior to the pubis, free of superimposition.
Common errors
- 1 CR angle insufficient results in foreshortened coccyx segments.
- 2 Patient rotation: coccyx not equidistant from the lateral walls of the pelvic opening.
- 3 Collimation not limited to the anatomy of interest on all four sides.
- 4 Pubic symphysis shadows coccygeal base.
Clinical indications
- Suspected coccygeal fracture from trauma or fall.
- Pathology of the coccyx.