The erector spinae is not a single muscle but a column of three parallel muscle groups, iliocostalis, longissimus, and spinalis, that together form the thick muscle mass running along both sides of the spine from the sacrum to the skull, responsible for extending and controlling the vertebral column. They work eccentrically to lower the trunk under gravity during forward bending and concentrically to raise it back upright, making them the key load-bearing muscles during every lifting task. Their segmental nerve supply means localised spinal nerve compression can produce a partial, patchy pattern of weakness within the group.
| Origin | Common tendon from the posterior iliac crest, posterior sacrum, and sacral spinous processes (collectively, the erector spinae aponeurosis) |
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| Insertion | Angles of the ribs and cervical transverse processes; Transverse processes of thoracic and cervical vertebrae and mastoid process; Spinous processes of thoracic and cervical vertebrae |
| Nerve Supply | Posterior rami of spinal nerves at each level they span |
| Blood Supply | Posterior branches of intercostal, lumbar, and lateral sacral arteries |
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During heavy lifting, the erector spinae generate the extension moment that keeps the trunk from collapsing under load, working synergistically with the thoracolumbar fascia and intra-abdominal pressure to protect the lumbar spine, their effective contribution explains why losing tension in them during a deadlift is a primary mechanism of lumbar disc injury.
Erector spinae overactivity is common in acute and chronic low back pain, where the superficial muscles guard the spine in place of well-coordinated deep stabilisers. Normally the erector spinae switch off near full forward bending as the posterior ligaments and fascia take the load (the flexion-relaxation phenomenon); loss of this relaxation is a recognised sign of altered motor control in chronic low back pain. Poor endurance on the Biering-Sorensen prone extension hold test is associated with a higher risk of future back pain. The erector spinae plane (ESP) block, injected deep to the muscle against the transverse processes, provides multilevel analgesia for thoracic, spinal and abdominal surgery. Trigger points in iliocostalis and longissimus can refer pain to the buttock and lateral hip.
The erector spinae are palpable as the prominent bilateral columns flanking the spinous processes throughout the lumbar and thoracic spine, they harden noticeably during extension against resistance or during trunk loading. Asymmetrical muscle bulk on inspection often indicates a compensatory scoliosis or unilateral inhibition pattern.
Tearing of erector spinae fibres from sudden loading or unguarded movement producing acute lumbar pain with protective spasm, local tenderness, and a Significantly restricted range of motion in all planes.
Trigger points within the iliocostalis and longissimus producing predictable referral patterns, lateral lumbar referral into the buttock, or midthoracic referral mimicking visceral pain, that are reproduced by direct sustained pressure on the trigger point.
