The pain behind the buttocks consider pear-shaped muscle syndrome, lumbar disc herniation, femoral head necrosis, osteoarthritis and other causes. 1. Piriformis muscle syndrome: mostly due to trauma or strain injury caused by the piriformis muscle edema compression of the sciatic nerve buttock pain, and to the back of the thighs. 2. Lumbar disc herniation: the herniated disc can appear sciatica when it presses the nerve, mainly radiating pain in the waist, buttocks and lower limbs, and some of them have numbness and muscle atrophy in the lower limbs. 3. Necrosis of the femoral head: Because necrosis of the femoral head can pull the synovial tissue at the hip joint, causing hip pain and walking limp. 4. Osteoarthritis: osteomalacia of the hip joint and narrowing of the joint space can cause hip joint activity limitation and buttock pain. There are many reasons for pain in the back of the buttocks, including bone tumors in the hip joint and acetabular fracture, etc. It is necessary to go to the hospital for further examination to clarify the cause of the disease and further treatment.