Injury to the tailbone (coccyx) generally happens with a fall. The visible sign of trauma will be bruising in the area. Sitting will be painful and the site itself will be very tender. An x-ray will have to be taken to determine if there is breakage or just bruising. For medical drawings of broken and disfigured coccyx go to this link: http://www.ktif.org/sacrococcygeal_exam.asp They have good information on injuries and the drawings show the possible disfigurations from breaks or arthritis.