Quadratus lumborum muscle

The quadratus lumborum muscle ([TA]: musculus quadratus lumborum, also costalis lumborum) is located on the posterolateral aspect of the spine lumbar. It is flattened and quadrilateral.

This muscle is made up of fibers that intersect in three directions:

• the cost-transverse fibers, ranging from the transverse apophysis of the L4, L3, L2 and L1 lumbar vertebrae to the lower edge of the twelfth rib.
• Iliotransverse fibers, which come from the iliac spine, from the inner lip and go to the transverse apophysis of the L4, L3, L2 and L1.
• Iliocostal fibers, which come from the iliac crest and reach the lower edge of the twelfth rib.

It originates from the iliolumbar ligament and lateral lip of the iliac crest and inserts on the lower border of the 12th rib and apex of the lumbar transverse processes.

It is innervated by spinal nerve T12 and spinal nerves L1 through L4.

Its function at a unilateral level: inflexion of the lumbar spine. Bilaterally: Extends the lumbar spine (producing hyperlordosis if strongly contracted along with the Psoas muscle) and lowers the 12th rib on expiration.