 Motor assessments are performed at 3-minute intervals for the first 30 minutes. Thereafter, the blocks are assessed at 15-minute intervals until the end of surgery. Results of the pinprick test were determined bilaterally at midclavicular level by using a 27-gauge needle. Motor block in the lower limb is assessed by a modified Bromage scale 0no paralysis, 1unable to raise extended leg, 2unable to flex knee,3unable to flex ankle. All of the assessments are made by an anesthetist who is blinded to the group assignment as well as to the dose injected. On the other hand, the investigators will compare the incidence of adverse reaction between the L2-3 and L3-4 group when the dose is evaluated as effective. 