Sciatic nerve block: subgluteal to popliteal fossa
COMPLEXITY: The sciatic nerve is a large structure and may be blocked at different levels to
provide regional anaesthesia and analgesia for a wide range of indications. Consideration must be given to both the indication for the nerve block and the location where the sciatic nerve is best visualized with ultrasound to determine
the best location to perform a block. Refer to Scanning tips for the lower extremities for a more detailed description of scanning the sciatic nerve.
Indications • Hip surgery (proximal) • Surgery of the sciatic distribution • Leg surgery, when combined with a lumbar plexus block • Analgesia (proximal for above the knee; distal for below the knee) • Sympathicolysis (achillodynia, diabetic gangrene, circulatory or wound-healing disorders, complex regional pain syndrome)
• Foot or ankle surgery. See Figures 4.42 to 4.52.
Ultrasound-guided technique Patient position: the patient may be positioned semi-prone, with the limb to be blocked uppermost (all approaches); supine, with the hip and knee fl exed (distal sciatic block); or supine (anterior approach). Landmarks: surface: superior iliac spine and ischial tuberosity, greater trochanter, and ischial tuberosity at gluteal fold and popliteal crease at knee; sonoanatomical: ischial tuberosity, greater trochanter, femur, and popliteal artery. Technique: place a curved transducer (3–7 MHz) on the posterior thigh. The hyperechoic sciatic nerve may be identifi ed between the gluteus maximus and adductor magnus muscles and posterior to the femur. In the mid-thigh, it may appear round or rectangular, while, distally, it appears circular and divides into two branches at its bifurcation. (Note: the nerve may be divided as proximal as the gluteal fold.) Distally, the sciatic nerve lies posterior (superfi cial) to the popliteal artery. Confi rm nerve identity, and follow the course of the nerve by scanning proximally and distally to confi rm anatomy before determining the appropriate level to block:
• Proximal sciatic (sacral plexus or subgluteal block) to block the hip • Mid-thigh or more proximal sciatic to block the knee • Distal sciatic, usually at or above the bifurcation, to block the knee and below.
An IP or OOP needle approach may be used; if using peripheral nerve stimulation, observe for an appropriately distal twitch. Inject 20–30 mL of local anaesthetic slowly to surround the nerve, observing spread. Needle: 10–15 cm, stimulating for single shot; 10–15 cm, Tuohy for continuous blockade.
Local anaesthetic: 0.75% ropivacaine. Comments: proximal (subgluteal) sciatic nerve may be diffi cult to identify with ultrasound, so landmarks may be required. Nerve stimulation is recommended if the nerve is deep.
FIGURE 4.42 Scan with a curvilinear probe to obtain a SAX view of the proximal sciatic nerve (patient in left lateral position). a Greater trochanter
b Knee a b FIGURE 4.43 Scan
with a linear probe to obtain a SAX view of the mid-femoral sciatic nerve; the needle is shown in an IP approach. The needle insertion point is on the groove between the biceps femoris and vastus lateralis muscles.
a Knee a FIGURE 4.44 Scan
with a linear probe to obtain a SAX view of the distal sciatic nerve. a Knee
FIGURE 4.45 SAX Anterior
view of the proximal sciatic nerve. a Sciatic n.
a Posterior FIGURE 4.46 SAX
–6 6
view of the proximal sciatic nerve CFD. a Sciatic n.
b Accompanying vessels
b a Anterior
FIGURE 4.47 SAX view of the mid-femoral sciatic nerve. a Sciatic n.
a Posterior Anterior a
FIGURE 4.48 SAX view of the distal sciatic nerve. a Sciatic n.
FIGURE 4.49 SAX view of the sciatic nerve bifurcation. a Common peroneal n. b Tibial n.
a b
FIGURE 4.50 SAX view of the sciatic nerve bifurcation. a Common peroneal n. b Tibial n.
a b
FIGURE 4.51 Probe position for proximal sciatic (subgluteal) block; insert the needle, using an IP approach. a Greater trochanter b Ischial tuberosity
a b
FIGURE 4.52 Probe position for distal sciatic (popliteal) block; insert the needle, using an IP approach. a Femoral condyle b Biceps femoris m. tendon