Sacroiliac arthritis can cause tailbone pain, because the sacroiliac joint and tailbone area related joints. So when inflammation occurs, there will be localized effusion, and the condition will continue to develop and there will be narrowing of the joint space, and localized osteophytes will cause stiffness of the joints when it is severe, which will affect squatting or sitting or standing so there will be pain in the tailbone. Simple sacroiliac arthritis can do hot compresses, physical therapy, baking electricity, take non-steroidal anti-inflammatory drugs. For compulsory spondylitis caused by invasion of the sacroiliac joints, blood tests need to be drawn to determine the HLA-B27, and anti-rheumatic drugs or biologics, such as Yunker, are needed. If left untreated, it can cause stiffness and ankylosis of the hip and sacroiliac joints. So when tailbone pain occurs you need to take films of the sacroiliac joints to see if you have sacroiliitis.