An X-ray of the sacro-coccygeal spine is a safe and painless test to visualise the sacrum (a triangular bone at the end of the spine), coccyx (known as tailbone, located just above the anus) and the surrounding soft tissues like muscles using small amount of radiation. The image is recorded on a special X-ray film. The X-ray image is black and white in colour. Dense structures such as the bones, appear white and softer body tissues, such as the skin and muscles appear darker. The actual exposure time to radiation is usually less than a second, although the overall test may take 20-30 minutes.