The single-injection suprasacral parallel shift (SSPS) lumbosacral plexus block is indicated for:

– preoperative analgesia before hip fracture surgery as an alternative to femoral nerve block

– postoperative analgesia after major hip or proximal thigh surgery

First the needle pierces the intertransverse ligament between the posterior upper margin of the sacrum and the posterior lower margin of the transverse process L5

Then the lumbosacral ligament that extends from the anterior lower margin of transverse process of L5 and the lateral part of the ala sacra.

The lumbar plexus and its terminal branches are contained partly inside the fascial space between the large anterior and the thin posterior lamina of the psoas major. In the lumbar paravertebral region, the two layers make a sort of a pocket towards the neural foramina of the vertebral column.

Below the transverse process (TP) of vertebral body L5 the psoas major deviates antero-laterally and creates a space – the socalled “psoas compartment” between the ala sacra and the psoas major. The terminal nerves of the lumbar plexus exit the psoas major at the level of the TP L5 and descend inside the psoas compartment together with the lumbosacral trunk (L4-L5) that is the most cranial component of the sacral plexus and supply the major part of the sacral innervation to the hip joint.

The muscles of the abdominal wall (external and internal obliques and transversus abdominis) are visualized.

The probe is moved dorsal until the quadratus lumborum is seen medial to the aponeurosis of the tranversus abdominis.

With a slight caudad tilt of the probe the body and transverse process (TP) of vertebral body L4 can be seen surrounded by the quadratus lumborum (QL) at the tip of the TP, erector spinae posterior to the TP and psoas major anterior to the TP.
This is the “shamrock sign” – the treefoil of the stem of the TP surrounded by the three muscle “leaves”.

Sauter A, Ullensvang K, Bendtsen TF, B

The picture on the right is the same as on the previous page but without colour codes.

The needle is inserted from the back of the patient practically parallel to the foot print of the probe. This makes it easy to visualize the needle with ultrasound.

Place the patient in the lateral decubitus position.

Place a low-frequency curved array probe in the axial plane in the flank just cranial to the iliac crest.

The muscles of the abdominal wall are visualized (see next page). The probe is moved dorsal until the quadratus lumborum is seen medial to the aponeurosis of the transversus abdominis.

With a slight caudad tilt of the probe the body and transverse process (TP) of vertebral body L4 can be seen surrounded by the “shamrock muscles” (see next page).

The lumbar plexus is visualized anterior to the TP (see second next page).

The needle is inserted from the back of the patient with in-plane technique and the needle tip is guided by ultrasound and electrical nerve stimulation to the target lumbar plexus (see third next page). Inject 20-30 mL of local anaesthetic.

The important target nerves for the lumbar plexus block are the femoral nerve (L2-L4), the obturator nerve (L2-L4), and the lateral femoral cutaneous nerve (L2-L3).

The other lumbar plexus nerves are not targetted with the lumbar plexus block, but are blocked selectively for some purposes (see relevant modules in this learning program): The iliohypogastric nerve (T12-L1), the ilioinguinal nerve (L1), and the genitofemoral nerve (L1-L2).

The femoral nerve innervates the iliopsoas, pectineus, sartorius, and quadriceps femoris muscles. It supplies sensory innervation to the hip joint, the anterior cutaneous branches of the thigh, the knee joint and via the saphenous nerve sensory branches to the knee region, the medial leg including branches to the medial ankle and subtalar joint capsules.

The obturator nerve innervates the adductors (longus, brevis, magnus), gracilis, pectineus, and obturator externus.

The lateral femoral cutaneous nerve supply sensory innervation to the lateral thigh.

The transducer is moved dorsally keeping the transverse orientation until the QL muscle is identified with its attachment to the lateral edge of the transverse process of the L4 vertebral body. With the psoas major muscle (PM) anteriorly, the erector spinae muscle (ESM) posteriorly and the QL muscle adherent to the apex of the transverse process, a well recognizable pattern of a shamrock with three leaves can be seen:
The transverse process of vertebral body L4 is visualized as the stem of the shamrock. The three leaves are the muscles: quadratus lumborum, psoas major, and the erector spinae muscle.

The needle is inserted in-plane to the transducer (lateral edge) and the tip of the needle is advanced through the QL muscle, penetrating the ventral proper fascia of the QL muscle and LA is finally injected between the QL and PM.