Posterior Abdominal Wall
Key Points
- The posterior abdominal wall muscles contribute to respiration and movement of the torso and thigh.
- The posterior abdominal wall is bound superiorly by the diaphragm, and, inferiorly, by the ilia of the pelvis.
Quadratus lumborum:
- Originates on the iliac crest and the transverse process of L5.
- Inserts on the transverse processes of L1-L4, and along the inferior border of rib 12 (intertextual variation regarding the specific origins and insertions of quadratus lumborum exists).
- It depresses and stabilizes rib 12, and laterally flexes the torso.
Diaphragm:
- Originates on the internal surface of the sternum, costal cartilages of ribs 6-12, and lumbar vertebrae L1-L3
- Contraction of the diaphragm expands the thoracic cavity, which decreases intrapulmonary pressure and induces inspiration (inhalation).
- Originates on the iliac fossa and lateral sacrum.
- Inserts on the lesser trochanter of the femur.
- Flexes the thigh at the hip.
Psoas major:
- Originates on the lateral aspects and intervertebral discs of vertebrae T12-L5 Inserts, with iliacus, on the lesser trochanter.
- Flexes the thigh at the hip.
Psoas minor:
- Originates on the lateral aspects and intervertebral discs of T12-L1
- Inserts on the pectineal line on the pelvis.
- Weak trunk flexor; it does not travel to the thigh with psoas major, and, therefore, does not act on the thigh.