Quadratus Lumborum is a flat, quadrilateral muscle that lies alongside the vertebral column. It is more or less irregular if form and is broader at its inferior attachment as compared to superior.
Origin of quadratus lumborum muscle:
Quadratus lumborum arises by aponeurotic fibers from the following structures;
- Iliolumbar ligament
- Adjoining part of the iliac crest
- Tips of transverse processes of lower lumbar vertebrae
Insertion of quadratus lumborum muscle:
The fibers of the muscle run upward and medially and are inserted into the lower border of twelfth rib and transverse processes of the upper four lumbar vertebrae.
The anterior aspect of the quadratus lumborum is covered by lumbar fascia. This fascia is thickened above to form the lateral arcuate ligament and below to form the iliolumbar ligament.
Blood supply of quadratus lumborum muscle:
Quadratus lumborum is supplied by the following blood vessels.
- Branches of the lumbar arteries
- Arteria lumbalis ima
- Lumbar branch of iliolumbar artery
- Branches of subcostal artery
Nerve supply to quadratus lumborum muscle:
Quadratus lumborum is innervated by the ventral rami of twelfth thoracic and upper three or four lumbar spinal nerves.
Actions of quadratus lumborum muscle:
Quadratus lumborum fixes the last rib by its contraction. It therefore acts as a muscle of inspiration by helping to stabilize the lower attachments of the diaphragm. The same action is also suggested to be responsible for providing a fixed base for controlled relaxation of the diaphragm needed for speech and singing.
When the pelvis is fixed, the quadratus lumborum acts upon the vertebral column and flexes it to the same side. When the quadratus muscles of both sides contract, they help to extend the lumbar part of vertebral column.