There are many reasons for pain behind the buttocks, which may be caused by sacroiliitis, ankylosing spondylitis, pyriformis syndrome, sciatic neuritis, osteoarthritis of the hip joint, lumbar disc herniation, etc. The details are as follows: 1. Pear-shaped muscle syndrome, sciatic neuritis caused by: if the patient has pear-shaped muscle syndrome, sciatic neuritis, will also lead to the back of the buttocks obvious pain symptoms. 3, hip osteoarthritis and so on caused by: if the patient has hip joint osteoarthritis, hip synovitis, the existence of the head of the femur necrosis, will also lead to pain in the back of the buttocks. 4, lumbar disc herniation, and so on caused by: if the patient has Herniated lumbar intervertebral disc, vertebral body slippage, spinal stenosis, tumor in the spinal canal, when compressed to the spinal cord nerve trunk, nerve root, will also lead to pain behind the buttocks.