There are the following reasons for low back pain and anal swelling: 1. After patients with posterior uterus get pelvic inflammation, due to congestion and edema of the inflamed tissues, which compresses the sacral subordinate nerves, patients will have low back pain. Especially when it comes to the ovulation period before and after menstruation, the exudate of inflamed tissues and the follicular fluid from follicular rupture flow down the lowest part of the pelvis, that is, the vaginal rectal fossa, and the patient will have obvious anal swelling.2. If the patient has ovarian cysts and uterine fibroids, which have grown to a certain extent, they will compress the sacral plexus nerves, and the patient will also have lumbar pain and anal swelling.3. Tumors in the pelvic cavity of the bladder or the rectum, Uterine cervix, these parts of the long malignant tumors, compression of the surrounding tissues, patients will have back pain, anal distension.