Common causes of back pain causing leg pain include sports injury, lumbar vertebral fracture, lumbar disc herniation, ankylosing spondylitis and so on. 1. Sports injury: due to strenuous exercise, overwork and other reasons, causing strain on the muscles of the lumbar back and lower limbs, the muscles are pulled during activities, which can cause pain. 2. Lumbar vertebral fracture: due to accidental fall during exercise, fall from height, etc., resulting in lumbar vertebral fracture and the surrounding soft tissue injury, the fracture can compress the spinal cord and nerve roots, causing pain in the lumbar back, pain in the lower limbs, numbness and other symptoms, and severe paralysis can occur. 3. Lumbar intervertebral disc herniation: due to age, chronic strain and other reasons, causing degenerative changes in the lumbar spine, fibrous ring rupture, nucleus pulposus protrudes and compresses the dural sac or nerve root at the back, and lumbar pain and lower extremity pain and numbness and other symptoms can occur. 4. Ankylosing spondylitis: it is a chronic inflammatory reaction that can involve multiple joints in the body, and the inflammatory stimulus causes stiffness and pain in the joints, which can be accompanied by pain in the lower back and lower limbs. Back pain caused by leg pain for more reasons, but also may be related to tumors, bone tuberculosis and other diseases, if the symptoms continue to be unrelieved, it is recommended to consult a doctor in a timely manner to clarify the cause of the disease, targeted treatment.