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

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”.

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.

Sauter A, Ullensvang K, Bendtsen TF, B

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 patient is placed in the lateral position with the side to be anaesthetized turned upwards.

A curved array transducer (6-2 MHz) is placed in the transverse plane at the abdominal flank immediately cranial to the iliac crest.

Surgical anaesthesia for hip surgery in combination with a sacral plexus block as an alternative to general or spinal anaesthesia

Postoperative analgesia after major hip surgery

Combined analgesia of the femoral, obturator and lateral femoral cutaneous nerves

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.

The transversalis fascia (TF) covers the deep surface of the transverse abdominis muscle (TAM), the quadratus lumborum muscle QLM) and the psoas major muscle (PMM). Anteriorly it covers the deep surface of the rectus abdominis muscle. It is covered by the peritoneum.

The layers of the abdominal wall from the outside are: external oblique muscle (EOM), internal oblique muscle (IOM) and TAM.

The latissimus dorsi muscle (LDM) and the erector spinae muscle (ESM) are superficial to the QL muscle.

The subcostal nerve (T12), ilioinguinal nerve (L1) and iliohypogastric nerve (L1) run across the anterior side of the quadratus lumborum (QL) muscle between the QL muscle and the transversalis fascia (TF).