Although surgical discectomy for disc herniation produces better short-term pain relief than conservative therapy, there is no convincing evidence for the long-term (10 years) advantage of surgery. Between 40% and 80% of patients undergoing back surgery continue to experience persistent pain, a condition called Failed Back Surgery Syndrome (FBSS). The symptoms of FBSS are of persistent or recurring low back pain and / or leg pain after one or more spinal operations. The precise cause of the pain can be difficult to determine due to the complex interaction of biological and psychosocial factors. Possible organic causes of FBSS include epidural fibrosis, arachnoiditis, mechanical factors, pressure induced changes in the nerve root, structural changes in the vertebral column, and lumbar degenerative disease. With a second surgical intervention for fibrosis, there is a 65-70% failure rate, with 15-20% of the patients reporting worsening of symptoms. Thus, repeated surgery tends to yield poorer results.