Sciatic Nerve Block

1. Sciatic Nerve Block Tiffany Tavernier

2. L4-S3 spinal nerve roots • Largest nerve trunk in the human body • Distribution = hamstrings, long head of biceps femoris, adductor magnus; part of hip and knee joint • Blocks skin of posterior aspect of thigh and entire leg below knee exception of skin of medial aspect of lower leg Some Basics….

3. Different Approaches.. • Classical Posterior Approach • Pt lies in lateral decubitus position • Landmarks: greater throchanter and posterior-superior iliac spine • Needle is inserted 4-5 cm distal to midpoint btw the two landmarks perpendicular to skin in all planes • Parasacral Approach • Pt lies in lateral decubitis position • Landmarks: posterior superior iliac spine and ischial tuberosity • Needle is inserted 6cm caudal to line btw the 2 in sagittal plane

4. Different approaches • Lithotomy • Pt is supine with hip flexed and upper leg perpendicular to torso • Landmarks: greater trochanter of femur and ischial tuberosity • Needle is inserted 4 cm in claudal direction midway between the 2 • Needle is advanced parallel to horizontal plane • Anterior approach • Pt is supine with legs extended • Landmarks: femoral crease and femoral arterial pulse • Needle inserted 405 cm distal from pulse of femoral artery and perpendicular to line of femoral crease

5. Posterior vs Anterior Approach • 100 pts undergoing minor knee surgery • Randomly divided by envelope to receive anterior or posterior approaches combined with femoral and lateral femoral cutaneous nerve blocks using US • 1% mepivacaine with short 1100m, 21 gauge • Block: 20mL of 1.5% mepivacaine with 1:400,000 epinephrine Anterior Approach • Nerve stimulator was used @ 2Hz to elicit foot plantar- or dorsiflexion Posterior Approach • Same as anterior, but without nerve stimulator.

6. Anterior vs Posterior Approach Measurements • both then placed in supine position with legs extended and femoral and lateral femoral cutaneous blocks were performed • Measurements of depth and size of sciatic nerve, needle depth, block execution time for sciatic nerve block, block execution time for all 3 blocks, time required for onset of sensory and motor blocks of sciatic nerve and duration of blockade of sciatic nerve were measured

7. Results • Sciatic nerve was located deeper in anterior approach • Both had similar block execution time for sciatic nerve block, but anterior approach took less time to complete all 3 blocks • Onset of sensory block for superficial peroneal, sural and tibial nerves was similar • Sensory block of posterior femoral cutaneous nerve was achieved less often with the anterior approach - less block of posterior area of thigh • Onset of motor block was similar with both approaches

8. Discussion • Although posterior femoral cutaneous nerve was rarely blocked with anterior approach, can still be used in knee surgery where thigh tourniquet is used  pts who required fentanyl was similar btw groups  tourniquet pain is not affected by presence of posterior femoral cutaneous nerve block