13.1.1 Anatomy

The lateral cutaneous nerve of the thigh (L2–L3) is a purely sensory nerve, which crosses the iliacus muscle lateral to the psoas after leaving the lumbar plexus. The nerve lies below the iliac fascia here and emerges through the fascia immediately below and medial to the anterior superior iliac spine, where it divides into anterior and posterior branches that run a few centimeters subcutaneously distal to the anterior superior iliac spine. The anterior branches supply the skin of the lateral thigh down to the knee where they are responsible for innervation of the knee region together with other sensory branches (also known as prepatellar plexus). The posterior branches innervate the skin of the lateral hip region below the greater trochanter as far as the middle of the thigh (Fig. 13.1, Fig. 13.2, Fig. 13.3, Fig. 13.4).

13.1.2 Techniques

13.1.3 Indications, Contraindications, Side Effects

13.1.4 Remarks on the Technique

The course of the nerve is very variable. This refers both to its individual division and to its area of innervation. In 4 to 6% of cases it is believed not to be present at all and can possibly be regarded as a branch of the femoral nerve (Bonniot 1922/23, Hovelacque 1927). Failure of anesthesia after a selective block can thus be explained anatomically. The close relationship between the femoral nerve and the lateral cutaneous nerve of the thigh is emphasized by reports on block effects in the region of the femoral nerve after conduction anesthesia of the lateral cutaneous nerve of the thigh (Sharrock 1980, Lonsdale 1988, Konder et al 1990).

To ensure a higher success rate, Shannon et al (1995) described an alternative PNS technique, which is initially performed transdermally. Morris et al (1999) point out that the paresthesia is reported synchronously with the nerve stimulator pulse and that injection of only 6 mL of local anesthetic leads to successful anesthesia. The possible advantages are a lower volume of local anesthetic and a higher success rate. Shannon reports an increase in the success rate from 85 to 100%. However, Rosenquist regards the procedure as relatively complex. For this reason, PNS is not recommended for routine use (Rosenquist and Lederhaas 1999) and is now replaced by ultrasound guidance.

An isolated block of the lateral cutaneous nerve of the thigh is useful as pain therapy for the treatment of meralgia paresthetica and for anesthesia—for example, for muscle biopsy and superficial operations on the lateral thigh (Jenkner 1983, Bonica 1984, Rybock 1989).

13.1.5 Block of the Lateral Cutaneous Nerve of the Thigh Using Ultrasound

Linear transducer: 12 MHz

Penetration depth: 3 to 5 cm

Needle: 5 cm

Scanning Technique

The lateral cutaneous nerve of the thigh is found in the short axis medial and distal to the anterior superior iliac spine (Fig. 13.5).

The patient lies supine. The lateral cutaneous nerve of the thigh crosses the sartorius muscle from medial to lateral, immediately medial and distal to the anterior superior iliac spine (Fig. 13.6). The course of the lateral cutaneous nerve of the thigh varies greatly; it sometimes crosses within or below the sartorius muscle (Fig. 13.7).

The nerve should not be looked for immediately at the attachment of the sartorius muscle to the superior iliac spine, because it is difficult to distinguish the nerve here in the hyperechoic muscle fascia tissue. Somewhat further medially and distally, the nerve can be visualized as a round hyperechoic structure (diameter 1–3 mm) on, in, or below the sartorius muscle. A few centimeters further distal, it is already lateral to the sartorius in the angle between the sartorius and the tensor fasciae latae muscles (Fig. 13.6).

Note

The best visualization of the lateral cutaneous nerve of the thigh is 1 to 2 cm medial and 4.5 to 5.5 cm distal to the anterior superior iliac spine. The skin–nerve distance here is 0.5 to 0.7 cm (Ng et al 2008).

13.2.1 Indication

Anesthesia and pain therapy for iliac crest bone graft harvesting.

13.2.2 Procedure

The area intended for removal of bone chips from the iliac crest is first infiltrated subcutaneously with a medium-acting or long-acting local anesthetic (Fig. 13.8). This is followed by injection as far as the periosteum of the iliac crest. This injection is given as a field block in order to infiltrate the entire harvesting area.

When bone graft harvesting is complete, the surgeon can place a catheter between the subcutaneous fat and the reconstructed musculofascial and periosteal tissue, tunneling the catheter out through the skin (Fig. 13.9).

Pain therapy can commence postoperatively with an intermittent injection of 20 mL of a long-acting local anesthetic. Alternatively, continuous local infiltration of the periosteum through an elastomer pump has proved useful. With this type of system, subcutaneous tunneling of the catheter outside the operation area (Fig. 13.10) is possible.

Local Anesthetics, dosage.

Anesthesia (single shot): 20 mL of ropivacaine 0.75% (7.5 mg/mL).

Analgesia: 20 mL of ropivacaine 0.375% (3.75 mg/mL) bolus or 5 mL of ropivacaine 0.2% (2 mg/mL) continuously.

13.3.1 Anatomy

The abdominal wall is supplied by the anterior branches of spinal nerves T7–T12 (intercostal nerves) and L1–L3 (iliohypogastric nerve [T12/L1], ilioinguinal nerve [L1], genitofemoral nerve [L1/L2], and lateral cutaneous nerve of the thigh [L2/L3]). These nerves lie between the internal oblique and the transversus abdominis muscles and give off cutaneous branches to the surface during their course (Fig. 13.12). The classical lateral TAP block usually leads only to a block of segments T10–L1. An additional subcostal block (possibly on both sides) is required for a block of segments T6–T9 (Børglum et al 2012). In this region, the transversus abdominis muscle lies directly below the rectus abdominis muscle (Hebbard et al 2010; Fig. 13.11).

13.3.2 Landmarks

The subcostal TAP block is performed immediately below the costal arch in the mid-clavicular line. The transversus abdominis lies directly below the rectus abdominis here. The layer between the two muscles is looked for (Fig. 13.11).

The classical lateral TAP block is performed at the lateral abdominal wall in the middle axillary line between the iliac crest and the 12th rib. The abdominal wall is formed from outside to inside by the following muscles: external oblique, internal oblique, transversus abdominis (Fig. 13.12). Below this is the peritoneal cavity with the corresponding organs (intestines, liver).

13.3.3 Indications and Contraindications

13.3.4 Procedure

The TAP block should be performed only under ultrasound guidance, as otherwise a high rate of failure and complications can be expected.

Ultrasound-Guided Transversus Abdominis Plane Block

Linear transducer: 6 to 13 MHz

Needle: 6 to 12 cm

Classical Lateral Transversus Abdominis Plane Block

The abdominal wall is visualized in the axial plane using ultrasound in the middle between the iliac crest and the lower costal arch in the mid-axillary line. The anterior part of the transducer should not extend beyond the anterior axillary line.

Before needle insertion, the following structures (from outside to inside) should be clearly defined (Fig. 13.12):

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  Fatty tissue

  
  
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  External oblique muscle

  
  
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  Internal oblique muscle

  
  
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  Transversus abdominis muscle

  
  
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  Intraperitoneal structures (intestine)

In case of doubt, the transducer can be moved toward the middle of the abdominal wall where the origins of the muscles are visualized and then followed laterally (Fig. 13.12).

After positioning the transducer, the puncture is made in plane; the puncture site should not be too close to the end of the transducer, so that a needle direction which is as tangential as possible can be maintained . The tip of the needle must be in the plane between the internal oblique and transversus abdominis muscles. The tip of the needle should be positioned posterior to the mid-axillary line as otherwise the lateral cutaneous branches of the intercostal nerves, which reach the surface from the layer between the internal oblique and the transversus abdominis muscles at around the mid-axillary line, will not be anesthetized.

The correct position of the needle is checked using 2 to 3 mL of local anesthetic, then the main dose of local anesthetic is injected (Fig. 13.13; ).

A catheter can be placed for a continuous technique (Fig. 13.14).

Subcostal Transversus Abdominis Plane Block

The transducer is positioned subcostally at about the midclavicular line at the lower costal arch. The puncture is made in plane from medial to lateral. The local anesthetic is injected in the layer between the rectus abdominis and the transversus abdominis, which lies here directly below the rectus abdominis (Fig. 13.11).

Local anesthetic, dosage.

Ropivacaine 0.375% (3.75 mg/mL) or mepivacaine 1% (10 mg/mL) at a volume of 20 mL (unilateral) to 40 mL (bilateral). For a complete block of the anterior abdominal wall (4 injections), 60 mL of ropivacaine 0.375% (3.75 mg/mL, 225 mg) have been described (Børglum et al 2012). All dosages apply to adults (> 50 kg).

Caution: Toxic plasma levels of ropivacaine have been measured at a total dose of 3 mg/kg body weight, corresponding to about 200 mg ropivacaine (Griffiths et al 2010; see also Chapter 21.6).

Continuous block: Ropivacaine 0.33% (3.3 mg/mL), 6 to 8 mL/h (max. 12 mL/h).

Tips and Tricks

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  Well suited for postoperative therapy after harvesting bone chips from the iliac crest. Catheter placement is recommended, as the duration of the effect of a single-shot technique is generally not sufficiently long, even if a longer-acting local anesthetic (e.g., ropivacaine) is used.

  
  
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  The catheter should be tunneled and drained out so that it can be fixated as far as possible from the operation region (Fig. 13.14).

  
  
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  For bilateral blocks, toxic plasma levels have been measured using a dosage of 3 mg/kg body weight of ropivacaine (corresponds approx. to 40 mL ropivacaine 0.5% (5 mg/mL) at 70 kg; Griffiths et al 2010).

  
  
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  The block can also be made under general anesthesia.

  
  
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  In the classical TAP block, a block of the femoral nerve is occasionally observed.

  
  
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  Skin, muscles, and the parietal peritoneum are anesthetized.

  
  
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  The visceral peritoneum is not anesthetized (if there is peritonitis, a dull peritoneal pain remains!).

13.4.1 Anatomy

The obturator nerve (L2–L4) arises from the lumbar plexus and is a nerve with both sensory and motor fibers. It runs on the medial border of the psoas major down through the lesser pelvis, penetrates the parietal pelvic fascia, and is accompanied by the obturator artery and vein. It passes together with them through the obturator foramen and obturator canal to the thigh (Fig. 13.15).

Here the nerve divides into the anterior (superficial) branch, which innervates the anterior adductors and the hip joint and ends in a cutaneous main branch that provides a variable sensory supply to the medial side of the thigh, and the posterior (deep) branch (Fig. 13.16), which is responsible for the posterior adductors and sends a branch to the posterior knee joint.

13.4.2 Techniques

Obturator Nerve Block (Classical Technique)

Landmarks and Position

The pubic tubercle is the bony landmark for obturator nerve block. The pubic tubercle on the side to be blocked is palpated and the puncture site is marked 1.5 cm lateral and distal to the pubic tubercle (Fig. 13.17).

The patient lies supine. The leg is slightly abducted.

Procedure

An 8-cm needle is inserted perpendicular to the underlying surface at the puncture site and advanced (Fig. 13.18). After 2 to 5 cm it reaches the horizontal superior ramus of the pubic bone. The distance to the pubic ramus is recorded and the needle is withdrawn somewhat; then the needle is slowly advanced in a more laterocaudal direction (more laterally and only slightly caudally) as far as 2 to 3 cm beyond the previously recorded depth. Here it passes the lower border of the pubic ramus and is close to the obturator canal (Fig. 13.19 and Fig. 13.20).

Following contractions of the adductors and after negative aspiration, 15 mL of a medium-acting or long-acting local anesthetic is injected. Because of the proximity of the obturator artery, there is a risk of accidental intravascular injection (Fig. 13.21 and Fig. 13.22) and a hematoma may develop. If the needle is advanced too far, it can pass through the obturator canal into the lesser pelvis minor, with the risk of injuring internal organs (Fig. 13.21).

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