Sudden back pain can not bend the most common reasons are muscle sprain, lumbar disc herniation, urinary stones, etc.. 1. Muscle sprain: If the patient has an incorrect posture during exercise, it is easy to cause lumbar muscle sprain, causing lumbar pain and lumbar bending restriction, and the patient suddenly lumbar pain can’t bend down. 2. Lumbar disc herniation: If the patient himself has lumbar disc herniation, overwork or improper posture may aggravate the lumbar disc herniation, which may cause lumbar pain and bending difficulty. 3. Urinary stones: if the patient has kidney stones or ureteral stones, when the patient’s body position changes, the stones may irritate the surrounding mucous membranes, which in turn causes pain in the lower back and difficulty in bending. Causes of sudden back pain can not bend more reasons, may also be associated with ankylosing spondylitis, compression fracture, lumbar muscle strain and other causes, if the symptoms are not relieved after rest, it is recommended to go to the hospital in a timely manner to find out the cause of the disease, by the doctor targeted treatment.