Popliteal sciatic nerve block (PSNB) is commonly practised regional anaesthesia and analgesia technique for below-knee surgeries. It is used alone or combined with a femoral or saphenous nerve block. The block can be performed blindly, guided by a nerve stimulator or ultrasound. The blind landmark-based technique is not preferred due to lower efficacy and higher complication rates.¹ The use of ultrasound (USG) allows a real-time visualisation and delivery of the medication at the target site, improving precision, accuracy and safety. The nerve block can be performed in the posterior, lateral and supine positions. Lateral and prone may pose challenges in morbidly obese, pregnant, hemodynamically unstable and/or spinal injury patients.² In supine position, the popliteal sciatic block can be performed by the posterior approach with out-of-plane needle entry, lateral or medial approach with lateral or medial in-plane needle entry respectively. The supine posterior out-of-plane approach provides the advantage of patient comfort, less chance of puncturing the popliteal vessels and shorter needle path.^{3, 4}

Recently, Mistry et al have described an USG-guided CAPS (Crosswise approach to popliteal sciatic) block in a case series of 5 patients successfully with the advantage of better patient comfort as there is no need of patient positioning, flexion of hip and knees and external assistance.²

We aim to compare the USG-guided posterior approach of popliteal sciatic block and CAPS block.