This condition is an irritation of the sciatic nerve, a thick nerve that branches from the lumbar spine and travels through the buttocks and down the back of each leg. An irritation of the sciatic nerve can result in radiating pain or numbness from the buttocks down through the legs.
The syndrome is caused by a contraction of the piriformis muscle in the gluteal region of the buttocks. This contraction can result from an overly tight piriformis muscle, trauma, or overuse of the muscle. When the piriformis muscle contracts, it puts pressure on the sciatic nerve (which runs beneath it).
Symptoms include a tingling feeling, pain, or numbness of the buttocks. In some cases the pain is felt only in the buttocks, but this condition can also cause soreness to radiate from the lower back down to the legs and sometimes to the feet.