Sudden back pain may have the following causes: 1, small joint disorders, especially in the elderly without obvious sprains, can also appear small joint disorders, sudden lumbar pain, lumbar afraid to move, to rest actively and symptomatic treatment, most can be cured. 2, acute sprain of the lumbar muscle, young people if the incorrect posture, lumbar sprain resulting in sudden lumbar pain. 3, kidney stones, when the kidney stones fall off and reach the ureteral stenosis, there will be sudden lumbar pain. When a kidney stone is dislodged and reaches the ureteral stenosis, sudden low back pain will occur, which can often be reflected to the abdomen, and blood tests, urine tests and ultrasound of the kidney are needed for further diagnosis. The diagnosis can only be confirmed by angiography.