Ultrasound-guided abdominal wall blocks are a recent innovation of the traditional landmark-based techniques of performing abdominal wall field blocks. 1 These blocks include the transverse abdominis plane (TAP) block (lateral/midaxillary and subcostal), 1–8 rectus sheath block, iliohypogastric and ilioinguinal nerve block, 8 and the quadratus lumborum block (QLB). 8–12 They are fairly simple to perform, largely devoid of complications, and produce sensory and motor blockade of the abdominal wall.
Muscles of the Anterior Abdominal Wall
The anterior abdominal wall is made of four large, flat muscles on either side of the midline. They are the external oblique muscle (EOM, Figs. 4–1 to 4–3), internal oblique muscle (IOM, Figs. 4–3 to 4–5), transversus abdominis muscle (TAM, Figs. 4–3, 4–6, and 4–7), and the rectus abdominis muscle (RAM, Figs. 4–3 and 4–6). Two other smaller muscles, the cremaster and the pyrimidalis, are also present. The EOM, IOM, and the TAM each end in a fibrous aponeurosis that extends up to the midline (Figs. 4–1, 4–4, and 4–6). The aponeuroses on either side fuse in the midline to form a median band called the linea alba. The RAM is longitudinal in shape, runs vertically on either side of the linea alba (Fig. 4–6), and is enclosed in a fibrous sheath called the “rectus sheath” (see later, Fig. 4–4).
Figure showing the innervation of the trunk and the abdominal wall. Note the aponeurosis of the external oblique muscle and the anterior and posterior wall of the rectus sheath (cutout view).
Figure showing the origin, insertion, and arrangement of the muscle fibers of the external oblique muscle.
Figure showing the anatomical arrangement of the muscles of the anterior abdominal wall (external oblique, internal oblique, transversus abdominis, and rectus abdominis) with their aponeurosis, including the rectus sheath. Note the three tendinous insertions on the anterior surface of the rectus abdominis muscle.
Figure showing the anatomical arrangement of the internal oblique muscle with its aponeurosis.
Figure showing the origin and insertion of the muscle fibers of the internal oblique deep to the external oblique muscle. Also note the direction of the muscle fibers of the internal oblique muscle (upwards and medially) relative to the external oblique muscle.
Figure showing the anatomical arrangement of the transversus abdominis muscle. Note the direction of the muscle fibers of the transversus ...