Outcomes assessment will done with Oswestry Disability Index (ODI) for the overall disability and the Japanese Orthopedic Association (JOA) score for the clinical symptoms and signs. The patients will receive evaluation before the surgery, at six months, and at the final follow-up examination. The range of ODI is 100 ~ 0 with a lower index corresponding to a better result. Significant improvement is defined as more than 15 points of improvement after the treatment. The range of JOA score is -3 ~ 29 with a higher score corresponding to a better result. The improvement rate based on JOA score is calculated as follows: (pre-operative score - post-operative score)/(29 - pre-operative score) × 100%. The clinical results are classified into four grades by the improvement rate: excellent (more than 75%), good (between 51% and 75%), fair (between 26% and 50%), and poor (less than 26%). The success of treatment is defined as more than 25% improvement rate in JOA score.20 At the final follow-up, we will inquire each patient if he or she is satisfied with the treatment results.