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Femoral nerve block is widely used for regional anesthesia and analgesia in many lower limb operations. Peripheral nerve stimulation of the femoral nerve may elicit 1 of 2 responses: contraction of the sartorius muscle through stimulation of its muscular branch or contraction of the quadriceps muscle through stimulation of its respective muscular branches. Historically, a quadriceps response has been preferred. We hypothesized that the success of femoral nerve block using a sartorius muscle evoked motor response is equivalent to that using quadriceps muscle twitch response. This prospective randomized double-blind controlled trial compared sartorius or quadriceps muscle evoked motor response as the end point for stimulation for femoral nerve block.Seventy-two patients scheduled for primary unilateral total knee arthroplasty were randomly assigned to undergo femoral nerve block using either the sartorius or the quadriceps evoked muscle response as an end point of stimulation. Motor block of the femoral and sensory block of the femoral, saphenous, and lateral femoral cutaneous nerves were assessed. The primary outcome was the quality of motor and sensory block of the femoral nerve 30 minutes after injection of 20 mL of 0.5% ropivacaine. Secondary outcomes were duration of femoral nerve block, time required to perform the nerve block, total dose of hydromorphone patient-controlled analgesia, and postoperative pain by visual analog score 24 hours after block insertion. In addition, the spread of local anesthetic and the position of the needle in relation to the femoral nerve were assessed by means of ultrasonography.There were no statistically significant differences in the proportion of patients with either complete alone or complete and partial block combined between quadriceps and sartorius groups 30 minutes after block insertion; femoral nerve (P = 0.49; P = 0.13), the saphenous nerve (P = 0.64; P = 0.21), or the lateral femoral cutaneous nerves (P = 0.2; P = 0.35). Patient-controlled analgesia hydromorphone consumption was significantly higher in the group that underwent sartorius muscle stimulation ([mean ± SD] 4.9 ± 3.6 mg [range, 0–13.2 mg] vs 3.1 ± 2.7 mg [range, 0–10.0 mg]; P = 0.024).Our study demonstrated that using sartorius or quadriceps evoked muscle twitch as an end point of stimulation was associated with an equivalent degree of femoral nerve block.