Tailbone (Sacrum and Coccyx) X-ray

What it is

The sacrum is the broad triangular bone at the base of the spine, fused into the back of the pelvis. Hanging off the end of it is the coccyx, or tailbone, a few small partly fused segments. This series is aimed specifically at that region, rather than at the lumbar spine above it or the pelvis around it, and takes at least two angles — a view from the front and a view from the side — because the tailbone curves forward and can only be seen in profile from the side. The bowel sitting in front of these bones tends to obscure them, so the images are not always as clean as elsewhere in the skeleton, and a normal-looking film does not rule out an injury to the soft tissues holding the bones together.

Why it is done

• To look for a break or a displaced tailbone after a backward fall onto a hard surface
• To examine persistent pain at the very base of the spine, especially pain that is worst when sitting
• To look at the sacrum after a high-energy injury, where it forms part of the pelvic ring
• To document the shape and angle of the tailbone in someone with long-term pain there

What to expect

No preparation; a gown and no metal at the waist. The patient lies on their back for one image and rolls onto their side for the other. Because the area of interest is small, the technologist may shield or tightly collimate the beam. Lying flat and then turning is the uncomfortable part when the tailbone is freshly injured, and sitting on the way in and out of the department may hurt more than the exam itself. The pictures take only minutes. Treatment for a bruised or broken tailbone is mostly the same either way — pressure relief and pain control — which is worth knowing before the study is done.

Questions worth asking

• Is the sacrum and the coccyx being billed as one exam or as two? Some departments order them separately.
• Will the result change the treatment? If the plan is the same whether a bone is cracked or bruised, that is worth raising before paying for the film.
• If lumbar spine or pelvis x-rays were taken at the same visit, do those already cover this region, and is each series charged separately?
• Was this ordered from an urgent care center that sends imaging out? If so, ask which facility performs and bills it.