Transversus abdominis muscle

Origin and insertion

The transversus abdominis has several origin points:

• Lateral one-third of the superior surface of the inguinal ligament and the associated iliac fascia
• Anterior two-thirds of the inner lip of iliac crest
• Thoracolumbar fascia between the iliac crest and the 12th rib
• Internal aspects of the lower six ribs and their costal cartilages

From their origin points, the transversus abdominis fibers course horizontally over the lateral abdominal wall towards the midline, oriented perpendicular to the linea alba. The muscle fibers go on to insert as follows:

• The inferior tendinous fibers originating from the inguinal ligament arch inferomedially over the inguinal canal and join the aponeurotic fibers of internal abdominal oblique to form the conjoint tendon. This tendon then inserts onto the pubic crest and pecten pubis.
• The remaining fibers extend into a broad aponeurosis that contributes to the formation of the rectus sheath and inserts on the linea alba.

Learn everything you need to know about transversus abdominis and the surrounding muscles of the abdominal wall with our interactive quizzes and videos.

Relations

Trasversus abdominis lies on the lateral abdominal wall, deep to the internal abdominal oblique and external abdominal oblique muscles. It comprises the deepest layer of the lateral abdominal wall.

The aponeurosis of the transversus abdominis muscle participates in comprising the rectus sheath. This is a multilayered aponeurosis that encloses the biggest portion of the rectus abdominis and pyramidalis muscles on their anterior and posterior sides.

The transversus abdominis aponeurosis makes up the posterior wall of the rectus sheath which covers the posterior upper three quarters of rectus abdominis, together with the aponeurosis of the internal abdominal oblique muscle. On the other hand, the aponeuroses of the transversus abdominis and internal abdominal oblique converge with the aponeurosis of external abdominal oblique anterior to the rectus abdominis and form the the lower quarter of the anterior wall of the rectus sheath. The point at which they converge is known as the arcuate line, and is located 2.5cm below the umbilicus.

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Below the free lower border of transversus abdominis, the transversalis fascia communicates with both internal and external oblique, as well as the inguinal ligament. Approximately 1/1.5 cm above inguinal ligament, between the midinguinal point (halfway point between the ASIS and pubic symphasis) and midpoint of the inguinal ligament, the transversalis fascia contains a round opening called the deep inguinal ring. Along the medial border of the deep inguinal ring, the free lower border of transversus abdominis occasionally gives off a band of fibers called the interfoveolar ligament.

Innervation

Transversus abdominis is mainly supplied by the terminal branches of the lower five intercostal nerves and the subcostal nerve, that arise from the lower six thoracic spinal nerves (T7-T12). Additionally, the iliohypogastric and ilioinguinal nerves (L1) contribute to the nervous supply of this muscle.

Blood supply

The transversus abdominis muscle receives its arterial blood supply from the following arteries:

• Lower posterior intercostal arteries, arising from the descending thoracic aorta. 
• Subcostal arteries, given off by the descending thoracic aorta.
• Superior epigastric artery, given off by the internal thoracic artery.
• Inferior epigastric and deep circumflex arteries given off by the external iliac artery.
• Superficial circumflex artery, a branch of the femoral artery.
• Posterior lumbar arteries, arising from the abdominal aorta.

Function

Along with other muscles of the abdominal wall, transversus abdominis plays an important role in maintaining normal abdominal wall tension. Therefore, these muscles have a protective as well as a supportive role, holding the abdominal organs in place. Additionally, weakness of transversus abdominis or other abdominal muscles increases the risk for abdominal hernias.

The lateral abdominal muscles, including transversus abdominis, also cause compression of the intra-abdominal viscera thereby increasing the intra-abdominal pressure. This action is facilitating expulsive functions such as forced expiration, micturition, defecation and final stages of childbirth.

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