CorpusHuman Anatomy
MuscularMuscle group

Erector spinae

Musculus erector spinae

Also known as: sacrospinalis, paraspinal muscles, iliocostalis, longissimus, spinalis, paraspinals

A massive column of intrinsic back muscle on either side of the spine, made up of iliocostalis, longissimus and spinalis. It is the chief extensor of the vertebral column.

Show on body map Muscles — Posterior View

Overview

The erector spinae lies in the groove between the spinous processes and the angles of the ribs, under the thoracolumbar fascia and the serratus posterior muscles. It arises by a thick common tendon from the posterior iliac crest, the posterior surface of the sacrum, the sacroiliac ligaments and the lumbar and lower thoracic spinous processes. It divides in the upper lumbar region into three columns.

- Iliocostalis (lateral): to the angles of the ribs and the cervical transverse processes. Its parts are lumborum, thoracis and cervicis.
- Longissimus (intermediate): to the transverse processes, ribs and the mastoid process (longissimus capitis). It is the longest and largest column.
- Spinalis (medial): spinous process to spinous process, mainly in the thoracic region.

Actions: acting on both sides, it extends the vertebral column and head, maintains upright posture and the lumbar lordosis, and controls forward bending by eccentric contraction. In full flexion it falls silent and load passes to ligaments, the flexion–relaxation phenomenon. That is why lifting from a fully stooped position strains the spine. Acting on one side, it laterally flexes the column. Like all intrinsic (epaxial) back muscles, it is supplied segmentally by dorsal rami of the spinal nerves.

Location

Paravertebral groove from the sacrum to the skull, deep to the thoracolumbar fascia.

Parts & subdivisions

  1. Iliocostalis (lumborum, thoracis, cervicis)
    Lateral column. From the iliac crest and sacrum to the angles of the ribs and the transverse processes of C4–C6.
  2. Longissimus (thoracis, cervicis, capitis)
    Intermediate column. To the transverse processes of the thoracic and cervical vertebrae, the ribs between their tubercles and angles, and the mastoid process.
  3. Spinalis (thoracis, cervicis, capitis)
    Medial column. From the upper lumbar and lower thoracic spinous processes to the upper thoracic and cervical spinous processes.

Anatomy

Origin

Common tendon from the posterior iliac crest, posterior sacrum, sacroiliac ligaments, and the sacral and lumbar (T11–L5) spinous processes and supraspinous ligament.

Insertion

Angles of the lower ribs and cervical transverse processes (iliocostalis); thoracic and cervical transverse processes, ribs and the mastoid process (longissimus); upper thoracic and cervical spinous processes (spinalis).

Action

Bilaterally: extends the vertebral column and head and resists flexion. Unilaterally: laterally flexes the column to the same side.

Innervation

Dorsal (posterior) rami of the spinal nerves, mainly their lateral branches (segmental).

Nerve roots

Dorsal rami C1–S3 (segmental, according to level)

Arterial supply

Dorsal branches of the posterior intercostal, subcostal, lumbar and lateral sacral arteries; deep cervical, vertebral and occipital arteries in the neck.

Relations

Enclosed in the thoracolumbar fascia: the posterior layer lies behind it, and the middle layer separates it from quadratus lumborum. Transversospinalis (multifidus, rotatores, semispinalis) lies deep and medial to it.

Function

  • Extends the vertebral column and head
  • Controls flexion (eccentric) and maintains posture
  • Lateral flexion of the trunk (unilaterally)

Clinical significance

Mechanical low back pain

Strain and spasm of the paraspinal muscles are among the commonest causes of acute low back pain. Spasm causes a list and loss of lordosis. Most episodes resolve with activity and analgesia. Red flags (cauda equina symptoms, weight loss, fever, trauma) must be excluded.

Lifting technique

Lifting with the spine fully flexed transfers the load from the inactive erector spinae to the posterior ligaments and discs. Lifting with the knees bent and the spine neutral keeps the muscles engaged.

Mnemonics

Lateral → medial

"I Love Spaghetti": Iliocostalis, Longissimus, Spinalis.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.