The sudden inability to bend the lumbar region because of pain is mainly seen in the following cases. 1. acute lumbar sprain, strain of the lumbar muscles caused by trauma or sprain, which in turn leads to pain, restricted activity, forward flexion, rotation, back extension and restricted activity of the lumbar spine. 2. lumbar disc herniation, mainly acute lumbar disc herniation, which leads to severe lumbar pain and restricted activity. 3. small joint disorder of the lumbar spine. Because of the lack of exercise, the ligaments of the small joints are relaxed, and the joint capsule suddenly appears to be stuck, resulting in neuralgia or lumbago.