Feasibility and Safety of Sciatic Nerve Paraneural Sheath Block Using a Mid-Femoral Lateral Approach

In clinical practice, the popliteal approach to sciatic nerve paraneural sheath block is the most commonly used. Studies have found that compared with extraneural injection, ultrasound-guided sciatic nerve paraneural sheath block via the popliteal approach has a faster onset and provides longer postoperative sensory and motor blockade. Paraneural sheath block aims to achieve efficient, rapid, and precise nerve blockade using a low volume of local anesthetic. However, the popliteal approach requires knee flexion for performance, necessitating the patient to be in a prone or lateral decubitus position. For patients unable to flex the knee or those with positioning difficulties due to conditions such as lower limb fractures, this method is less applicable. For the above reasons, the popliteal sciatic nerve block has certain limitations.

The mid-femoral lateral approach demonstrates unique advantages: First, the patient can maintain a supine position throughout the procedure, significantly enhancing comfort and compliance. Second, the sciatic nerve is relatively superficial at this level, offering good ultrasonographic visualization and being distant from major blood vessels and nerves. This makes it applicable even in obese patients with thick subcutaneous fat and suboptimal ultrasound images, theoretically enhancing procedural safety. Therefore, it is considered an effective solution for patients with positioning restrictions, such as those with lower limb fractures and severe pain, holding high potential for clinical promotion and research significance.

Although the anatomical feasibility of this approach has been preliminarily confirmed, its practical feasibility and safety require validation through clinical studies. In particular, whether a successful "paraneural sheath block" can be consistently achieved at the mid-femoral lateral level, similar to the classic popliteal approach, remains to be explored. While some literature suggests its theoretical feasibility, there is a lack of prospective, systematic clinical research evidence to support its practical application feasibility (e.g., block efficacy, procedural difficulty, success rate) and safety (e.g., complication rates, incidence of nerve injury).

This study is designed as a randomized controlled trial aiming to evaluate the feasibility and safety of ultrasound-guided mid-femoral lateral approach sciatic nerve paraneural sheath block. The goal is to provide a new sciatic nerve block option for clinical practice that offers greater patient comfort and more precise blockade, facilitating its use for specific patient populations and less experienced operators.

• Block Success Rate [Time frame: At 30 minutes after block completion.]
• Sensory Block Onset Time [Time frame: From the end of injection until complete sensory block is achieved (assessed every 30 seconds), up to 30 minutes.]
• Duration of Sensory Block [Time frame: From block onset until first pain complaint, assessed up to 48 hours postoperatively.]
• Motor Block Onset Time [Time frame: From the end of injection until complete motor block is achieved (assessed every 30 seconds), up to 30 minutes.]
• Duration of Motor Block [Time frame: From block onset until full motor recovery, assessed up to 48 hours postoperatively.]
• Time to First Request for Rescue Analgesia [Time frame: From end of surgery until first rescue request, assessed up to 24 hours postoperatively.]
• Total Consumption of Rescue Analgesics within 24 Hours [Time frame: Within 24 hours after surgery.]
• Postoperative Pain Intensity (NRS Scores) [Time frame: At 4, 8, and 24 hours after surgery.]
• Incidence of Rebound Pain [Time frame: Within 48 hours after block resolution.]
• Procedure-Related Times [Time frame: During the block procedure.]
• Number of Needle Redirections [Time frame: During the block procedure.]
• Incidence of Complications [Time frame: From block procedure up to 1 week postoperatively.]