Iliocostalis lumborum muscle

At a glance

English

Iliocostalis lumborum muscle

Latin (TA2)

Musculus iliocostalis lumborum

System

Muscle

Region

Back

Side

Paired, left and right

About the iliocostalis lumborum muscle

Erector spinae is the large mass of back muscles lying in the groove beside the vertebral column, and it is arranged in three columns. Iliocostalis is the outermost, lying lateral to longissimus and closest to the line where the back muscles meet the muscles of the trunk wall. Its lowest section, iliocostalis lumborum, sits in the lower back deep to serratus posterior inferior and the thoracolumbar fascia.

It takes origin from the common tendon of erector spinae, which is anchored to the iliac crest, the dorsal sacrum, the lumbar spines up to about T11 and the thoracolumbar fascia. From this broad base its fibres rise and separate into flattened tendons that attach beneath the rib angles of roughly ribs 6 or 7 to 12. In many descriptions a lumbar part also reaches the tips of the lumbar transverse processes. Iliocostalis thoracis continues the column upward, beginning medial to these tendons.

Acting on one side, the muscle bends the lumbar spine and lower thorax towards that side. Acting on both sides, it extends the lower back and holds the trunk upright against gravity, and it controls bending forward by paying out slowly. By pulling down on the lower ribs it may also steady them during forced breathing out.

The muscle is supplied segment by segment by lateral branches of the dorsal rami of the lower thoracic and lumbar spinal nerves, and blood comes from the lumbar, subcostal and lower posterior intercostal arteries. It is a common site of muscle strain and spasm in acute low back pain, and its outer edge forms the visible ridge beside the lumbar spine in a lean back.

Attachments, action and supply

Origin

Common erector spinae tendon from the iliac crest, back of the sacrum, thoracolumbar fascia and lumbar spines.

Insertion

Lower edges of the rib angles of roughly ribs 6 or 7 to 12, and the tips of the lumbar transverse processes.

Action

Bends the trunk to its own side on one side; extends the lower back and keeps the trunk upright on both sides.

Nerve supply

Lateral branches of the dorsal rami of the lower thoracic and lumbar spinal nerves.

Blood supply

Dorsal branches of the lumbar, subcostal and lower posterior intercostal arteries.