Arcuate line of rectus sheath

The arcuate line of rectus sheath (a.k.a. the linea semicircularis) is a curved anatomical landmark located on the posterior layer of rectus sheath in the lower part of the anterior abdominal wall. It marks the level at which the arrangement of the aponeuroses forming the rectus sheath changes.

The rectus sheath surrounds the rectus abdominis muscle and is formed by the aponeuroses of the three flat abdominal muscles:

• External oblique

• Internal oblique

• Transversus abdominis

Above the Arcuate Line

Above the arcuate line, the rectus abdominis muscle is enclosed by both anterior and posterior layers of the rectus sheath:

• The anterior wall is formed by the external oblique aponeurosis and the anterior lamina of the internal oblique aponeurosis.

• The posterior wall is formed by the posterior lamina of the internal oblique aponeurosis together with the transversus abdominis aponeurosis.

This arrangement provides strong support to the rectus muscle from both sides.

Below the Arcuate Line

Below the arcuate line, all three aponeuroses pass anterior to the rectus abdominis muscle. Consequently:

• The posterior wall of the rectus sheath is absent and the rectus muscle lies directly on the:

  • Transversalis fascia

  • Extraperitoneal fat

  • Parietal peritoneum

This makes the lower part of the anterior abdominal wall relatively weaker compared to the region above the arcuate line.

--- Location

The arcuate line of rectus sheath is typically located approximately one-third of the distance between the umbilicus and pubic symphysis; around 5 cm inferior to the umbilicus.