Comparison of sciatic nerve block quality achieved using the anterior and posterior approaches: a randomised trial

BACKGROUND: The co-administration of sciatic and femoral nerve blocks can provide anaesthesia and analgesia in patients undergoing lower extremity surgeries. Several approaches to achieve sciatic nerve block have been described, including anterior and posterior approaches. METHODS: In total, 58 study patients were randomly assigned to receive either anterior (group A, n = 29) or posterior (group P, n = 29) sciatic nerve block. Thereafter, the following parameters were determined: sensory and motor block start and end times, time to first fentanyl requirement after blockade but before the start of the operation, time to first fentanyl requirement after the start of the operation, mean fentanyl dose administered after blockade but before the start of the operation, mean fentanyl dose after the start of the operation, time to first diclofenac sodium dose, and total dose of diclofenac sodium required. The trial was retrospectively registered on 11 July 2018. RESULTS: The time to initiation of sensory block was significantly shorter in group P than in group A (7.70 ± 2.05 min and 12.88 ± 4.87 min, respectively; p = 0.01). Group P also had a significantly shorter time to first fentanyl requirement after block but before the start of the operation (00.00 ± 00.00 min for group P and 4.05 ± 7.47 min for group A; p < 0.01), significantly higher mean fentanyl dose per patient after block but before the start of the operation (44.03 ± 23.78 μg for group P and 31.20 ± 27.79 μg for group A), significantly longer time to first fentanyl requirement after the start of the operation (16.24 ± 7.13 min for group P and 00.00 ± 00.00 min for group A; p = 0.01), and significantly lower mean fentanyl dose per patient after the start of the operation (11.51 ± 2.87 μg for group P and 147.75 ± 22.30 μg for group A). Patient satisfaction (p < 0.01), anaesthesia quality (p = 0.006), and surgical quality (p = 0.047) were significantly higher in group P. CONCLUSIONS: Anterior and posterior approaches can be used to achieve sciatic nerve block in patients undergoing surgery for malleolar fractures. However, better anaesthesia and pain control results can be obtained if analgesia is administered preoperatively in patients with a posterior approach block and after the start of the operation in patients with an anterior approach block.