Posterior Abdominal Wall Anatomy

Layers of the Posterior Abdominal Wall

• Outer layer: Transversalis fascia (a layer of connective tissue)
• Middle layer: Posterior abdominal wall muscles (erector spinae, latissimus dorsi, and quadratus lumborum)
• Inner layer: Parietal peritoneum (a layer of peritoneum lining the abdominal cavity)

Muscles of the Posterior Abdominal Wall

• Erector Spinae:
  • Consists of three columns: iliocostalis, longissimus, and spinalis
  • Extends from the sacrum to the thorax
  • Functions: extends and rotates the vertebral column
• Latissimus Dorsi:
  • Originates from the thoracolumbar fascia and spinous processes of the lower thoracic vertebrae
  • Inserts into the humerus
  • Functions: adducts, extends, and internally rotates the shoulder joint
• Quadratus Lumborum:
  • Originates from the posterior abdominal wall and iliac crest
  • Inserts into the 12th rib
  • Functions: fixes the 12th rib during respiration and assists in lateral flexion of the vertebral column

Other Structures of the Posterior Abdominal Wall

• Lumbar Triangle:
  • A weak area in the posterior abdominal wall, bounded by the latissimus dorsi, external oblique, and iliac crest
  • A potential site for herniation
• Lumbar Plexus:
  • A network of nerves formed by the ventral branches of L1-L4
  • Supplies the lower limb
• Kidneys and Adrenal Glands:
  • Located on either side of the vertebral column
  • Protected by the posterior abdominal wall muscles and transversalis fascia