Handa 9781496386441 Full Sample Chap 1

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SECTION I  Preparing for Surgery

Sheath of rectus (anterior layer)

I

External oblique

Sheath of rectus (posterior layer)

Arcuate line

Internal oblique

Transversalis fascia

Inguinal ligament

FIGURE 1.2  Abdominal wall mus- cles and rectus sheath. (The original illustration is in the Max Brödel Archives in the Department of Art as Applied to Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, USA. Used with permission.)

Round lig.

Rectus cut

Pyramidalis

of ribs 10 through 12, the pecten pubis via the conjoint tendon, and the linea alba. In most areas, the fibers of the internal oblique are perpendicular to the fibers of the external oblique muscle; however, in the lower abdomen, the internal oblique fibers arch somewhat more caudally and run in a direction similar to those of the external oblique muscle. As the name transversus abdominis implies, the fibers of the deepest of the three flat muscles have a primarily transverse orientation. They arise from the costal cartilages of the lower six (7 through 12) ribs, the thoracolumbar fascia, the iliac crest, and the lat- eral third of the inguinal ligament. Their distal attach- ments are to the pubic crest, the pecten pubis via the conjoint tendon, and the linea alba. The caudal portion of the transversus abdominis muscle is fused with the internal oblique muscle to form the inguinal falx, also called the conjoint tendon. This fusion explains why, during transverse incisions of the lower abdomen, only two layers are discernible at the lateral portion of the incision. The aponeurotic fibers of the conjoint tendon attach to the pubic crest and pecten pubis. This tendon lies immediately behind the superficial inguinal ring, and along with the transversalis fascia, forms the pos- terior wall of the inguinal canal. A weakening of the conjoint tendon can lead to a direct inguinal hernia. The inferior free edge of the transversus abdominis and internal oblique muscle fibers form the superior bound- ary (roof) of the inguinal canal.

Although the fibers of the flank muscles are not strictly parallel to one another, their primarily trans- verse orientation and the transverse pull of their attached muscular fibers place vertical suture lines in the rectus sheath under more tension than transverse ones. For this reason, vertical incisions are more prone

to dehiscence. Rectus Sheath

The muscle fibers of the external oblique become apo- neurotic approximately at the midclavicular line. In the lower abdomen, this demarcation gradually devel- ops more laterally ( FIG. 1.3 ). At its inferior margin, the muscle fibers of the internal oblique extend farther toward the midline than do the muscle fibers of the external oblique. Because of this, fibers of the internal oblique muscle are found underneath the aponeurotic portion of the external oblique muscle during a low transverse incision ( FIG. 1.4 ). In addition, between the internal oblique and trans- versus abdominis muscles lies a neurovascular plane, which corresponds to a similar plane in the intercostal spaces. This plane contains the nerves and arteries that supply the anterolateral abdominal wall. In the anterior part of the abdominal wall, these nerves and vessels exit the neurovascular plane and lie mostly in the subcuta- neous tissue. Although not often possible, the nerves should be identified and spared, and strategies used to avoid injury within the neurovascular plane should be

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