The erector spinae is the primary extensor muscle mass of the spine, consisting of three longitudinal columns that fill the gutters on either side of the vertebral column from the sacrum to the cervical spine. The three columns — iliocostalis laterally, longissimus intermediately, and spinalis medially — each have thoracic, lumbar, and cervical portions. Together they are the most tonically active muscles in the body in standing and sitting postures, continuously working against gravity.
| Origin | Common aponeurotic origin from the posterior iliac crest, sacrum, and lower lumbar spinous processes |
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| Insertion | Three columns: iliocostalis (lateral to ribs and cervical transverse processes), longissimus (intermediate to thoracic transverse processes and ribs), spinalis (medial between spinous processes) |
| Nerve Supply | Posterior rami of spinal nerves at each level |
| Blood Supply | Posterior intercostal, lumbar, and cervical arteries |
| Actions | Bilateral: extension of the spine from lumbar to cervical; Unilateral: ipsilateral lateral flexion; Maintains upright posture against gravitational flexion moment |
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During forward bending, the erector spinae elongate eccentrically to control spinal flexion against gravity. At approximately 90 degrees of forward flexion, the erector spinae relax completely as the posterior ligamentous system takes over the flexion control load — the flexion-relaxation phenomenon. Failure of this relaxation in chronic low back pain is a diagnostic sign of altered motor control.
The thoracolumbar erector spinae are the primary muscles targeted in spinal extension strength testing and endurance assessment. The Biering-Sorensen test of prone trunk extension endurance predicts future low back pain development — those with weaker erector spinae are at significantly higher risk. Erector spinae plane (ESP) block, injected lateral to the thoracic transverse processes deep to the erector spinae, provides effective multilevel analgesia for thoracic and abdominal surgery.
The erector spinae mass is palpable as the bilateral columns on either side of the spinous processes from the sacrum to the cervical spine, most prominent in the lumbar region where the longissimus and iliocostalis are both large.
Acute or overuse injury to the extensor mass producing lumbar or thoracic back pain with restricted extension, one of the most common musculoskeletal presentations managed with early mobilisation and progressive loading.
