Abstract: Based on the dissection of the hips of 112 cadavers (including the local specimen of the corpse) , research was conducted to determine RSR (the relatively safe region) of the operation, to provide anatomical basis for the treatment of Piriformis Syndrome by needle knife subcutaneous release operation, and to check the feasibility in clinical validation of RSR of needle knife subcutaneous release operation in the treatment of piriformis syndrome.Results showed that the scalloped area enclosed by the projective line of inferior branch of superior gluteal nerve and the most lateral protrusive point of the greater trochanter was the relatively safe region; there were not important nerves and blood vessels in this region, so it would not damage the nerve and blood vessels while operating in this region.The 20 subject patients were closely observed for about 12 to 18 months after operation. All of their situations were significantly improved. What’s more, no nerve and vasculars injury and other severe complications occurred to them.

Key words: needle knife subcutaneous release operation, relatively safe region , Piriformis Syndrome