Muscles - Posterior Abdominal Wall Flashcards
What are the posterior abdominal wall muscles?
1) Quadratus lumborum
2) Psoas major
3) Psoas minor
4) Iliacus
5) Diaphragm
Quadratus lumborum?
This muscle is located laterally in the posterior abdominal wall. It is a thick muscular sheet which is quadrilateral in shape. The muscle is positioned superficially to the psoas major.
Origin - iliac crest and the iliolumbar ligament.
Insertion - fibres travel superomedially, inserting onto the transverse processes of L1-L4 and the inferior border of the 12th rib.
Innervation - anterior rami of T12-L4 nerves.
Actions - Extension and lateral flexion of the vertebral column. It also fixes the 12th rib during inspiration, so that the contraction of diaphragm is not wasted.
Psoas major?
This muscle is located near the midline of the posterior abdominal wall, immediately lateral to the lumbar vertebrae.
Origin - transverse process and vertebral bodies of T12-L5.
Insertion - moves inferiorly and laterally, running deep to the inguinal ligament, and attaching to the lesser trochanter of the femur.
Innervation - anterior rami of L1-L3 nerves.
Action - Flexion of the thigh at the hip and lateral flexion of the vertebral column
Psoas minor?
This muscle is only present in 60% of the population. It is located anterior to the psoas major.
Origin - vertebral bodies of the T12 and L1 vertebrae
Insertion - pectineal line
Innervation - anterior rami of the L1 spinal nerve
Actions - flexion of the vertebral column
Iliacus?
This is a fan-shaped muscle that is situated inferiorly on the posterior abdominal wall. It combines with the psoas major to form the iliopsoas - the major flexor of the thigh.
Origin - surface of the iliac fossa and anterior inferior iliac spine.
Insertion - fibres combine with the tendon of the psoas major and insert onto the lesser trochanter of the femur.
Innervation - femoral nerve (L2-L4)
Actions - flexion and lateral rotation of the thigh of the hip joint
Diaphragm?
The posterior aspect of the diaphragm is considered to be part of the posterior abdominal wall.
Clinical relevance - psoas sign?
The psoas sign is a medical sign that indicates irritation to the iliopsoas group of muscles. The sign is elicited by flexion of the thigh at the hip. The test is positive if the patient reports lower abdominal pain.
A right sided psoas sign is an indication of appendicitis. As the iliopsoas contracts, it comes into contracts with the inflamed appendix, producing pain.
Fascia of the posterior abdominal wall?
A layer of fascia (sheet of connective tissue) lies between the parietal peritoneum and the muscles of the posterior abdominal wall. This fascia is continuous with the transversalis fascia of the anterolateral abdominal wall.
Whilst the fascia is one continuous sheet, it is anatomically coorect to name the fascia according to the structures it overlies.
Psoas fascia?
The psoas fascia covers the psoas major muscle. It is attached to the lumbar vertebrae medially, continous with the thoracolumbar fascia laterally and continuous with the iliac fascia inferiorly.
Thoracolumbar fascia?
The thoracolumbar fascia consists of three layers; posterior, middle and anterior. Muscles are enclosed between these layers:
- Quadratus lumborum - between the anterior and middle layers.
- Deep back muscles - between the middle and posterior layers.
The posterior layer extends between the 12th rib and the iliac crest posteriorly. Laterally the fascia meets the internal oblique and transversus abdominis muscles, but not the external oblique. As it forms these attachments it covers the latissimus dorsi.
The anterior layer attaches to the anterior aspect of the transverse processes of the lumbar vertebrae, the 12th rib and the iliac crest. Laterally, the fascia is continuous with aponeurotic origin of the transversus abdominis muscle. Superiorly the fascia thickens to become the lateral arcuate ligament, which joins the iliolumbar ligaments inferiorly.
