What are the main muscles of the posterior abdominal wall?

The posterior abdominal wall is primarily formed by three muscles on each side: psoas major, iliacus, and quadratus lumborum. They provide structural support and aid in posture, trunk movement, and hip flexion.

What is the function of the psoas major muscle?

The psoas major acts as the primary flexor of the thigh at the hip when acting from above, and it flexes the trunk on the thigh when acting from below. It is supplied by the ventral rami of L2–L4 spinal nerves.

Where does the iliacus muscle originate and insert?

The iliacus originates from the upper two-thirds of the iliac fossa, inner lip of the iliac crest, and lateral surface of the upper sacrum. It fuses with the psoas major and inserts on the anterior lesser trochanter of the femur.

What actions does the quadratus lumborum perform?

The quadratus lumborum laterally flexes the lumbar spine, fixes the 12th rib during inspiration, and extends the lumbar spine when acting bilaterally. It is supplied by the ventral rami of T12–L3/4 spinal nerves.

What is a psoas abscess and how does it present clinically?

A psoas abscess is a collection of pus within the psoas sheath, often due to tubercular infection in lumbar vertebrae. It may track down beneath the inguinal ligament into the femoral triangle, presenting as a soft swelling in the groin.

What is the psoas minor muscle and is it always present?

The psoas minor is a small muscle that lies anterior to the psoas major and acts as a weak trunk flexor. It is absent in about 50% of individuals, supplied by a branch of the L1 spinal nerve.

What nerves are associated with the psoas major muscle?

The psoas major has important nerve relations: the lumbar plexus is embedded within it, with nerves emerging from its lateral border; the genitofemoral nerve runs on its anterior surface; and medial structures include the lumbosacral trunk, iliolumbar artery, and obturator nerve.

Posterior Abdominal Wall Muscles – Psoas, Iliacus & QL

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