Posterior layer of rectus sheath

The posterior layer of rectus sheath is the fibrous layer located behind the rectus abdominis muscle in the upper part of the anterior abdominal wall.

The composition of the posterior layer of rectus sheath differs above and below the arcuate line level:

Above the Arcuate Line

Above the arcuate line, the posterior layer is formed by:

• The posterior lamina of the internal oblique aponeurosis

• The aponeurosis of the transversus abdominis muscle

At this level, the internal oblique aponeurosis splits into anterior and posterior layers, contributing to both walls of the rectus sheath.

Below the Arcuate Line

Below the arcuate line, the posterior layer of rectus sheath is absent because:

• The aponeuroses of the external oblique, internal oblique, and transversus abdominis muscles all pass anterior to the rectus abdominis muscle.

Consequently, posterior to the rectus muscle, lie only:

• Transversalis fascia

• Extraperitoneal fat

• Parietal peritoneum

This creates a relatively weaker area in the lower anterior abdominal wall.

Functions

The posterior layer of the rectus sheath:

• Provides posterior support to the rectus abdominis muscle

• Helps strengthen the anterior abdominal wall

• Separates the rectus muscle from abdominal viscera

• Assists in maintaining abdominal wall integrity during movement and increases in intraabdominal pressure