Sudden inability to straighten the back may be related to lumbar sprain, lumbar disc herniation, ankylosing spondylitis, etc., which can be treated by bed rest, medication or surgery. 1. Lumbar sprain: Lumbar sprain is usually caused by jumping, falling, lifting heavy objects with improper posture resulting in lumbar muscle injury, which leads to lumbar straightness. At this time, bed rest can be used to relieve the pain, and avoid physical activities that may cause secondary injury to the lumbar region. 2. Lumbar disc herniation: Lumbar disc herniation refers to a syndrome in which the nucleus pulposus presses on the nerves due to the degeneration of the lumbar discs and the rupture of the annulus fibrosus, which can cause lumbar pain and lead to a sudden inability to straighten up the back. Nucleus pulposus removal can be used to relieve the pressure on the nerve roots and relieve the patient’s discomfort. 3. Ankylosing spondylitis: Ankylosing spondylitis can damage and destroy the spinal joints, hip joints, etc., resulting in the patient’s back not being able to straighten up. When ankylosing spondylitis is diagnosed, non-steroidal anti-inflammatory drugs such as Meloxicam tablets should be taken under doctor’s supervision to improve the symptoms. When the symptoms of a sudden inability to straighten the back appear, you should seek medical attention in time to have the cause of the disease diagnosed and treated by a professional doctor.