The causes of numbness of the buttocks and dryness of stool after falling on the buttocks include constipation, sciatic nerve injury, cauda equina injury and so on. 1. Constipation: if the patient himself has too little water, often stay up late and other bad habits, then the phenomenon of dry stools can occur, due to the fall of the buttocks triggered by tissue damage, so the numbness. 2. Sciatic nerve injury: If the sciatic nerve is damaged after falling on the buttocks, the defecation function of the patient can be impaired, so that the patient does not have bowel movement for a long time, and the phenomenon of dry bowel movement occurs. 3. Cauda equina nerve injury: If the cauda equina nerve, which controls defecation, is injured after a fall, the nerve will be slowed down and the human body will not be able to excrete stools, and the water will be absorbed too much, thus there will be dry stools. It is suggested that after falling on the buttocks numbness and dry stool phenomenon, please consult a doctor in time.