The iliacus fascia covers the iliacus and psoas muscles in the pelvis and descends into the thigh with these muscles (Fig. 28.1). The femoral nerve lies anterior to the psoas muscle initially, with the lateral cutaneous nerve of the thigh lateral to the psoas muscle and obturator nerve medial. At the inguinal ligament, the femoral nerve lies in a gutter between the psoas and iliacus muscles. These nerves thus lie beneath the iliacus fascia (Fig. 28.1). Spread of local anesthetic (Figs 28.2 and 28.3) beneath the iliacus fascia produces a higher success rate of anesthesia of the femoral nerve, lateral cutaneous nerve of the thigh, and obturator nerves than the femoral nerve block technique.

Figure 28.1 Cadaver structures illustrating anatomy relevant to the iliacus block technique. 1: anterior superior iliac spine; 2: pubic tubercle; 3: inguinal ligament with abdominal muscles sectioned and removed; 4: iliacus muscle; 5: iliacus fascia; 6: femoral nerve; 7: lateral cutaneous nerve of thigh; 8: genitofemoral nerve. The obturator nerve is not visible on the medial aspect of the psoas muscle.

Figure 28.2 Axial T1-weighted MR image after injection of 40 mL of contrast, showing spread of injectate. Compare with Figure 21.5. Note contrast surrounding femoral and obturator nerves. Spread is via the plane between the iliacus and psoas muscles. 1: psoas muscle; 2: iliacus muscle; 3: femoral nerve; 4: obturator nerve.

Figure 28.3 (Right) Sagittal T1-weighted MR image demonstrating spread of contrast toward the anterior superior iliac spine, where the lateral cutaneous nerve of the thigh lies. Compare with Figure 21.6. 1: psoas muscle; 2: contrast spread; 3: anterior superior iliac spine; 4: iliacus muscle.

Surface anatomy

The main landmarks for iliacus block are the anterior superior iliac spine, pubic tubercle, and inguinal ligament. The pubic tubercle can be palpated three fingers’ breadth from the midline, along the upper border of the pubis.

The inguinal ligament is outlined by a line connecting the anterior superior iliac spine and the pubic tubercle. The inguinal ligament is divided into equal thirds. At the junction between the outer one-third and inner two-thirds, a perpendicular line is drawn; 1 cm along this line is the needle insertion point (Fig. 28.4). The femoral artery can be palpated 2–3 cm more medially in the groin.

Figure 28.4 Landmarks for the iliacus block. The anterior superior iliac spine, pubic tubercle, and inguinal ligament are outlined. The inguinal ligament is divided into equal thirds. At the junction between the outer one-third and inner two-thirds, a perpendicular line is drawn extending into the thigh; 1 cm down this line is the needle insertion point.

It is important to remember that with a fractured neck of femur these relations may change.

Sonoanatomy

The iliacus muscle is found lateral to the femoral artery in the groin, lying outside the femoral sheath and beneath the fascia lata and iliaca. A transverse ultrasound transducer orientation is used (Fig. 28.5). The fascia lata and iliaca are seen as hyperechoic lines. The appearance of the iliacus muscle on ultrasound is hypoechoic with hyperechoic fascial boundaries (Fig. 28.6).

Figure 28.5 Global view of the block field for the ultrasound-guided iliacus block.

Figure 28.6 Transverse ultrasound image at the level of the inguinal crease showing sonoanatomy relevant to the iliacus block using a 2-5 MHz curvilinear ultrasound transducer. FL: fascia lata; FI: fascia iliaca; IM: iliacus muscle; FA: femoral artery; FN: femoral nerve.

A scanning routine is used. To identify the iliacus muscle, the transducer is placed over the femoral vessels on the anterior thigh at 90° to the expected orientation of the nerve and vessels (Fig. 28.5). Identify the fascia lata. Move the tranducer laterally. Identify the fascia iliaca as a hyperechoic line deep to the fascia lata. The iliacus muscle lies beneath.

Technique

Landmark-based approach

As for all regional anesthetic procedures, after checking that emergency equipment is complete and in working order, intravenous access, ECG, pulse oximetry, and blood pressure monitoring are established. Asepsis is observed.

The patient is placed in the supine position, with the operator standing on the side to be blocked, at the level of the patient’s thigh. Having outlined landmarks, the needle insertion point is infiltrated with local anesthetic using a 25-G needle. An 18-G Tuohy needle is inserted perpendicular to the skin (Fig. 28.7). An initial loss of resistance is identified on penetrating the fascia lata. A second loss of resistance indicates penetration of the fascia iliaca. No muscle response is sought. Incremental injection of local anesthetic (30–40 mL) is made with repeated aspiration. No resistance to injection should be present.

Figure 28.7 Iliacus block technique. The epidural needle is inserted perpendicular to the skin. A loss of resistance technique is used to identify the iliacus fascia.

As this is a compartment block, volume of local anesthetic is important. The compartment is highly vascular, suggesting that inclusion of vasoconstrictor agents, such as adrenaline (epinephrine) and clonidine, with local anesthetic, may be useful.

Ultrasound-guided approach

The ultrasound machine and block tray should be placed in positions which allow the operator to simultaneously scan the patient and take items from the block tray with minimal movement. This setup may take some forethought but is a worthwhile exercise, and will facilitate successful regional anesthesia.

The operator stands on the side to be blocked, and with the patient in a supine position (Fig. 28.5). The skin is disinfected with antiseptic solution and draped. A sterile sheath (CIVCO Medical Instruments, Kalona, IA, USA) is applied over the ultrasound transducer with sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA). Another layer of sterile gel is placed between the sterile sheath and the skin. The infrainguinal region is scanned with a 6–13 MHz linear transducer. The ultrasound screen should be made to look like the scanning field. That is, the right side of the screen represents the right side of the field. Adjustable ultrasound variables such as scanning mode, depth of field, and gain are optimized.

A transverse image of the iliacus muscle is obtained (Fig. 28.6). The iliacus muscle is kept in the center of the field of view. The needle entry site is at the lateral-most end of the linear transducer. A 23-gauge needle is advanced under real-time ultrasound guidance and local anesthetic is deposited along the needle entry path. A free hand technique rather than the use of a needle guide is preferred. An 18-GA 21-Tuohy needle is inserted parallel to the axis of the beam of the ultrasound transducer, with the bevel facing the transducer (Fig. 28.8). The needle is attached to sterile extension tubing, which is connected to a 20-mL syringe and flushed with local anesthetic solution to remove all air from the system. It is then introduced at the lateral-most end of the transducer and visualized along its entire path to the iliacus muscle (Fig. 28.9). It is important not to advance the needle without good visualization. This may require needle or ultrasound transducer adjustment.