Posterior Abdominal Wall Muscles

Posterior Abdominal Wall Muscles

• The posterior abdominal wall is located behind the abdominal cavity and is formed by muscles, fascia, and the vertebral column.
• The diaphragm, a sheet of muscle separating the thoracic and abdominal cavities, contributes to the posterior abdominal wall.
• The lumbar vertebrae are large in humans, due to upright bipedal posture, shaping the posterior abdominal wall.
• The psoas major muscle runs from the transverse processes of lumbar vertebrae (T12-L5) to the lesser trochanter of the femur.
• Psoas major is a primary hip flexor and aids in lateral flexion of the vertebral column.
• Psoas minor, a smaller muscle, runs from vertebral bodies T12 and L1 to the superior ramus of the pubis bone. Its function is less clear, but it may assist in trunk flexion.
• The iliacus muscle originates from the iliac crest and ilium wing, also attaching to the lesser trochanter of the femur. Like psoas major, it's a hip flexor.
• Iliacus and psoas major blend, forming a single iliopsoas tendon at the insertion point.
• Iliacus also contributes to lateral rotation of the femur at the hip joint, especially during hip flexion.
• The quadratus lumborum is a flat, rectangular muscle attached to the iliac crest, ilio-lumbar ligament, transverse processes of L1-L4 vertebrae, and the 12th rib.
• Quadratus lumborum facilitates lateral flexion of the lumbar vertebral column and helps with extension, when the column is flexed.
• The lumbar plexus, also known as the lumbosacral plexus, is in the posterior abdominal wall, forming nerves like the femoral and sciatic nerves.

Fascia of the Posterior Abdominal Wall

• Fascia is a connective tissue sheet, surrounding and supporting muscles and structures, shaping the body.
• The outer layer of connective tissue surrounding a muscle can become part of a larger fascial sheet.
• The thoracic lumbar fascia is a broad sheet, deep in the posterior abdominal wall. It connects posterior abdominal wall muscles, including quadratus lumborum and latissimus dorsi.
• The peritoneum, a serous membrane, lines the abdominal cavity, covering viscera and creating mesentery. It provides support, but is separate from the fascia.

Nerve Innervation of Posterior Abdominal Wall Muscles

• Psoas major and quadratus lumborum receive innervation from anterior rami of spinal nerves (T12-L4), due to their proximity to the vertebral column.
• The iliacus muscle's innervation comes from the femoral nerve, originating from the lumbar plexus (L2-L4), following the femoral vessels.