Patient Position: Lateral with surgical side up.

Indications: Surgical anesthesia and postoperative analgesia of the posterior thigh and leg, as well as the knee, ankle, and foot.

Needle Size: 21-gauge, 100-mm insulated stimulating needle.

Volume: 15 to 20 mL of ropivacaine 0.5% or 0.2% depending on the indication

Anatomic Landmarks: The ischial tuberosity and the posterior superior iliac spine (PSIS) are major surface landmarks for this block. The sciatic nerve is comprised of L4 through S3 ventral rami and exits the pelvis through the inferior portion of the greater sciatic foramen, deep (anterior) to the piriformis muscle. It lies deep to the gluteus maximus muscle and medial to both the gluteus medius and gluteus minimus. It is the most lateral of all structures passing inferior to the piriformis muscle. Medial to it lies the internal pudendal and inferior gluteal vessels and nerves. Occasionally the sciatic nerve divides prior to entering the gluteal region, with the common fibular nerve passing superior to, or through the piriformis muscle.

Approach and Technique: The PSIS and the inferior aspect of the ischial tuberosity are palpated and marked, and a line drawn between the two points (Fig. 12-1). The needle insertion lies along this line, slightly caudal to the superior aspect of the gluteal cleft, or approximately 6–8 cm caudal to the PSIS. The needle is connected to a nerve stimulator (2 Hz, 1.5 mA, 0.1 ms) and advanced in a parasagittal plane. If the sacrum is contacted, the needle is withdrawn and redirected slightly laterally, walking off the border of the sacrum into the greater sciatic foramen. The endpoint of needle advancement is a sustained sciatic stimulation eliciting foot plantar flexion/inversion (tibial nerve) or dorsiflexion/eversion (common fibular nerve) motor
response with a current less than 0.5 mA (Fig. 12-2). Following negative aspiration for blood, local anesthetic is slowly injected in 5-mL increments, with intermittent aspiration.

Patient Position: Lateral, with the operative site up and the knee flexed (Sims position).

Indications: Anesthesia and immediate postoperative analgesia for surgery at and below the knee or requiring the use of a thigh tourniquet for more than 30 minutes.

Needle Size: 21-gauge, 150-mm insulated needle.

Volume: 15 to 20 mL.

Anatomic Landmarks: The greater trochanter, the posterosuperior iliac spine, and the sacral hiatus.

Approach and Technique: The center of the greater trochanter and the posterior iliac spine are identified and marked, and a line is drawn between these two points. Next, the sacral hiatus is identified and marked. Another line is drawn from the greater trochanter to the sacral hiatus. A perpendicular line is drawn to the midpoint of the greater trochanter–posterior iliac spine line. The intersection between this line and the greater trochanter–sacral hiatus line represents the point of insertion of the needle. The insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced perpendicular to the skin (Fig. 12-3). The stimulation of the sciatic nerve produces a flexion of the
foot and toes or an inversion of the foot (tibial nerve) or a dorsiflexion of the foot and extension of the toes or an eversion of the foot (common peroneal nerve). The needle is positioned to maintain the same motor response with a current of less than 0.5 mA. After negative aspiration for blood, the local anesthetic is injected slowly, with repeated aspiration for blood every 5 mL.

Patient Position: The patient is placed in the lateral decubitus position with the side to be blocked up. Both lower extremities are flexed slightly at the hips and knees with the buttocks forming a 90° angle with the bed.

Indications: Anesthesia and postoperative analgesia for any surgical procedure in the lower extremity involving the posterior thigh and any area distal to the knee excluding the medial side of the leg, which is innervated by the saphenous nerve, a branch of the femoral nerve.

Needle Size: Usually a 21-gauge, 100-mm insulated needle suffices. In some cases a 20-gauge, 150-mm insulated needle is necessary.

Anesthetic Volume: 25 to 35 mL.

Anatomic Landmarks: The intergluteal sulcus between the buttocks is the only landmark for this approach.

Approach and Technique: This simple approach is based on the fact that the sciatic nerve runs parallel to and about 10 cm from the midline (intergluteal sulcus) in all adults regardless of gender and body habitus. Thus, the block can be performed at 10 cm from the midline at about any point in the gluteal area including the subgluteal fold. In the gluteal area it is usually performed lateral to the midpoint of the intergluteal sulcus only because this point is easy to visualize and teach. The 10-cm measurement must be linear as shown in Figure 12-4, disregarding any individual contour on the patient’s buttocks.
This linear distance reflects the distance between the midline and the area immediately lateral to the ischial tuberosity where the nerve runs.

A local anesthetic wheal is raised at this point and an insulated needle connected to a nerve stimulator (around 1.5 mA, 1 Hz, 0.1 ms) is then slowly advanced parallel to the midline (parallel to the bed) as shown in Figure 12-5. Usually a motor twitch of the gluteus maximus can be easily seen as the needle passes through this muscle and continues to be visible until the needle reaches the deep surface of the gluteus maximus. The needle then needs to traverse the small amount of connective tissue deep to this muscle before reaching the sciatic nerve. The tip of the needle is then carefully manipulated until a response is still visible at 0.5 mA. The injection of local anesthetic is given slowly with frequent aspirations.

If the needle fails to elicit a sciatic nerve response, the reposition is easy since the nerve could only be either lateral or medial to the needle. The needle is withdrawn completely and a very small (10°) correction is made to the angle of insertion, first lateral and then if necessary medial.