Caudal plexus pain is characterized by a clinical foreign body sensation, resulting in an unpleasant and unpleasant sensation of a foreign body being held in the buttock groove. It is clinically common, especially after a fall with the buttocks on the ground, and is significantly more common in women than in men. The caudal plexus, which consists of sacral 5 caudal 1 and some anterior branches of sacral 3 and 4 nerves, coincides with the lower fibers of the paravertebral sympathetic trunk. So what are the reasons for the unpleasant and unpleasant feeling in the buttock groove like clamping a foreign object? 1, trauma: mainly due to the sacrococcygeal area in the fall by direct violence, women can also be damaged during childbirth. 2, pelvic disorders: gynecological disorders, prostatitis and hemorrhoids are common. Tumor: mainly sacrococcygeal tumor. 4.Others: such as long-term sitting posture can also cause the sacrococcygeal degeneration and osteophytes.