Transversus abdominis muscle

The transversus abdominis muscle is the deepest of the flat muscles of the anterolateral abdominal wall. It lies deep to the internal abdominal oblique muscle and is characterised by horizontally oriented fibres that provide strong support to the abdominal viscera.

Attachments

The muscle originates from the internal surfaces of the lower six costal cartilages (ribs 7-12), the thoracolumbar fascia, the iliac crest, and the lateral third of the inguinal ligament. Its fibres run transversely and insert into the linea alba via an aponeurosis, as well as the pubic crest and pecten pubis through the conjoint tendon.

Blood supply

The transversus abdominis is supplied by the lower posterior intercostal arteries, subcostal artery, deep circumflex iliac artery, and inferior epigastric artery.

Innervation

It is innervated by the thoracoabdominal (lower posterior intercostal) nerves (T7-T11), subcostal nerve (T12), and the iliohypogastric and ilioinguinal nerves (L1).

Functions

Functionally, the muscle compresses and supports the abdominal viscera, increases intraabdominal pressure, and assists in forced expiration. It also contributes significantly to core stability and maintenance of posture.

Conjoint tendon

The lower fibres of the muscle join with those of the internal abdominal oblique to form the conjoint tendon (inguinal falx), which reinforces the medial part of the posterior wall of the inguinal canal. Clinically, weakness of the transversus abdominis and conjoint tendon may predispose to direct inguinal hernias.

Contribution to the rectus sheath

The aponeurosis of the transversus abdominis muscle contributes to the rectus sheath by passing posterior to the rectus abdominis above the arcuate line and anterior to it below the arcuate line.