Objective To evaluate the efficacy of ultrasound-guided modified anterior approach to sciatic nerve block ( SNB) for orthopedic surgery with general anesthesia. Methods Ninety American So-ciety of Anesthesiology physical status Ⅰ or Ⅱpatients of both sexes, aged 18-64 yr, weighing 19-28 kg∕m2 , scheduled for elective knee joint or distal orthopedic surgery, were divided into 3 groups ( n=30 each) using a random number table method: modified anterior approach ( the puncture needle was almost perpendicular to the ultrasound beam) group, anterior approach group and posterior approach group. SNB ( injecting 0. 5％ ropivacaine 20 ml) combined with femoral nerve block ( injecting 0. 5％ ropivacaine 15-20 ml) was performed under ultrasound guidance. Surgery was completed under combination of the laryngeal mask and combined intravenous-inhalational anesthesia. When the respiratory rate ≥20 beats∕min and∕or the increase in heart rate was more than 20％ of the baseline value, sufentanil 1μg∕time was intravenously injected. When visual analog scale ( VAS) score ≥4 within 24 h after surgery, celecoxib capsules 0. 2 g was taken orally for analgesia. The depth of sciatic nerve, needling depth, sharpness score of needle ima-ging under ultrasound, and operation time and duration of SNB were recorded. VAS scores at rest and dur-ing activity were recorded at 6, 8, 10, 12 and 24 h after surgery. The amount of sufentanil consumed dur-ing surgery and use of celecoxib capsules within 24 h after surgery were recorded. The development of ad-verse reactions such as hematoma at the puncture site, nausea and vomiting was also recorded after surgery. Results Compared with posterior approach group, the depth of sciatic nerve and needling depth were sig-nificantly increased, the operation time of SNB was prolonged, the duration of SNB was shortened, the in-traoperative consumption of sufentanil was increased, VAS scores at rest and during activity were increased at 10 h after surgery, and the sharpness score of needle imaging was increased in modified anterior approach and anterior approach groups (P<0. 05). Compared with anterior approach group, the sharpness score of needle imaging was significantly increased, and VAS scores during activity were decreased at 24 h after sur-gery in modified anterior approach group ( P<0. 05) . There was no significant difference in the requirement for celecoxib capsules within 24 h after surgery or occurrence of adverse reactions among the three groups ( P>0. 05) . Conclusion Although ultrasound-guided modified anterior approach to SNB provides compara-ble efficacy with anterior approach to SNB and is not as good as posterior approach to SNB when used for or-thopedic surgery with general anesthesia, modified anterior approach to SNB is easy to operate, with clear images under ultrasound.