The iliocostalis lumborum is the lumbar portion of the iliocostalis, forming the most lateral column of the erector spinae in the lower back. It runs from the iliac crest to the lower rib angles, serving as a primary lateral stabiliser and extensor of the lumbar spine. Its large cross-sectional area in the lumbar region makes it the dominant erector spinae muscle at this level and a primary target of spinal manual therapy and exercise-based rehabilitation for low back pain.
| Origin | Iliac crest and thoracolumbar fascia |
|---|---|
| Insertion | Angles of ribs 6 through 12 |
| Nerve Supply | Posterior rami of spinal nerves T7 through L3 |
| Blood Supply | Posterior intercostal arteries; Lumbar arteries |
| Actions | Extension of the lumbar spine when acting bilaterally; Ipsilateral lateral flexion of the lumbar spine; Depression of the ribs during forced expiration |
|---|
During lifting tasks it contracts powerfully to resist forward flexion of the lumbar spine, acting eccentrically during the lowering phase and concentrically during the return to upright, a loading pattern that explains its vulnerability to acute strain.
Iliocostalis lumborum strains are one of the most common acute low back pain mechanisms, produced by sudden unguarded lifting or trunk rotation. The muscle is assessed during the modified Biering-Sorensen test of prone trunk extension endurance, which has been shown to predict future low back pain episodes. Trigger points in the iliocostalis lumborum refer pain across the low back, into the buttock, and occasionally to the upper thigh.
Palpable as the most lateral band of the erector spinae mass immediately lateral to the longissimus, running parallel to the spinous processes in the lumbar region and becoming hard during resisted trunk extension.
Acute muscle tear from sudden unguarded lifting or rotation producing sharp unilateral low back pain with extension restriction, one of the most common presentations of acute mechanical back pain.
