Anatomy, Bony Pelvis and Lower Limb: Psoas Major

Excerpt

The psoas muscle is among the most significant muscles that overlie the vertebral column. It is a long fusiform muscle on either side of the vertebral column and the brim of the lesser pelvis. At its distal end, it combines with the iliacus muscle to form the iliopsoas muscle. The psoas muscle has traditionally described having a deep and superficial segment. The deeper segment of the muscle originates from the first four lumbar vertebrae, while the superficial segment originates along the lateral surface of the distal thoracic vertebrae and from adjacent intervertebral discs. In between the deep and superficial layers, one can find the lumbar plexus. At the distal end, the psoas muscle combines with the iliacus muscle to form the iliopsoas muscle which is encircled by the dense iliac fascia. The common tendon attaches on the lesser trochanter of the femur: the muscle during contraction of the fibers lead to external rotation and abduction of the femur. The orientation of the muscle changes from the superior-inferior direction of the upper portion to a horizontal direction toward anterior of the middle portion reaching the pubic branch and passing under the inguinal ligament, and to an oblique direction toward posterior of the distal portion of the tendon inserting on the lesser trochanter. The inconsistent psoas minor muscle completes the psoas muscle.

The psoas major muscle has a biomechanical and postural function during both moving and static states. It is also involved in the metabolic function used in the clinical assessment of some diseases, as well as mood and stress disorders as a cause of low back pain.