text: what does numbness in your leg that does not go away a sign of? started as back pain, then numbness on small area on back of thigh and buttox, then moved down all the way almost to the back of knee. started a week ago to the day. inflamation and/or physical impingement of nerve(s) as they come out of your spine - likely involving the sciatic nerve.  i'd go see a legit healthcare provider and keep a dated log of the symptoms progression for future reference.  good luck.