Pain at the back of the thigh under the buttocks, consider trauma, lumbar disc herniation, pear-shaped muscle syndrome, etc.. 1. Trauma: If the local area suffers a violent impact, it will cause soft tissue damage and pain, usually accompanied by swelling, subcutaneous bruising and other symptoms. 2. Herniated lumbar disc: Herniated lumbar disc is a symptom caused by degeneration of the lumbar disc and partial or total rupture of the annulus fibrosus, which leads to the protrusion of the nucleus pulposus to stimulate or compress the nerve root, and it will cause pain in the lumbar region and radiating pain in the lower limbs, which can be radiated from the buttocks along the back of the thigh to the calf and the back of the foot. 3. Piriformis syndrome: Piriformis syndrome is caused by traumatic bleeding, adhesion, scar formation, resulting in hypertrophy of the piriformis muscle, compression of the sciatic nerve and a series of symptoms. The main manifestation is pain in the buttocks on the affected side, and the pain will radiate along the sciatic nerve to the lower limbs on the same side. There may be other causes of pain in the back of the thighs under the buttocks, it is recommended that the patient consult the hospital in a timely manner, to clarify the cause of the disease and then give targeted treatment.