Pain in the middle bone of the buttocks when sitting on a stool may be caused by trauma, soft tissue injury, synovitis and other reasons. 1. Trauma: It is mainly caused by the fracture of the tailbone due to external impact, bumping, falling or other violent reasons, which will cause pain. 2. Soft tissue injury: due to sedentary, poor sitting posture and other reasons, caused by the tailbone or peripheral fascia and other soft tissue injuries, sitting on the stool local stimulation, resulting in pain. 3. synovitis: due to cartilage degeneration and osteophytes, sedentary and other reasons, leading to the tailbone periphery synovitis, due to inflammation of the stimulus, can appear to sit on a stool in the middle of the buttocks bone pain phenomenon. The pain in the middle bone of the buttocks when sitting on a stool should go to the hospital in time and follow the doctor’s instructions for treatment to avoid delaying the condition.