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Erector spinae muscles

The erector spinae is a large group of paired muscles and tendons located on either side of the vertebral column. It forms the chief extensor of the vertebral column and plays a vital role in maintaining upright posture and controlling spinal movements.

It is divided into three vertical columns of muscles:

  1. Iliocostalis (most lateral)

  2. Longissimus (intermediate)

  3. Spinalis (most medial)

Together, they span from the sacrum and iliac crest to the skull, bridging the axial skeleton from pelvis to cranium. They are clinically important in spinal stability, rehabilitation, and imaging for back pain, trauma, or infection.

Synonyms

  • Sacrospinalis muscles

  • Spinal extensors

  • Paraspinal muscles (general term, though includes other groups too)

Origin and Insertion

  • Origin (common tendon):

    • Posterior part of the iliac crest

    • Posterior surface of the sacrum

    • Sacroiliac ligaments

    • Spinous processes of T11–L5 vertebrae

  • Course and Insertion (by column):

    • Iliocostalis: Inserts on ribs and cervical transverse processes

    • Longissimus: Inserts on ribs, transverse processes of thoracic and cervical vertebrae, and mastoid process of the temporal bone

    • Spinalis: Inserts on spinous processes of upper thoracic vertebrae and skull (occipital bone)

Nerve Supply

  • Dorsal rami of spinal nerves along the entire length of the spine

Arterial Supply

  • Lumbar arteries

  • Posterior intercostal arteries

  • Deep cervical artery

  • Iliolumbar artery (lower portion)

Venous Drainage

  • Posterior intercostal veins

  • Lumbar veins

  • Deep cervical vein

  • Tributaries draining into azygos system and inferior vena cava

Function

  • Extension of the vertebral column and head

  • Lateral flexion of the spine when acting unilaterally

  • Maintenance of erect posture

  • Dynamic stabilization of vertebral column during movement and load bearing

MRI Appearance

T1-weighted images:

  • Muscles show low-to-intermediate signal intensity

  • Surrounding fat planes appear bright

  • Fatty infiltration or chronic atrophy appears as areas of high signal intensity

T2-weighted images:

  • Normal muscles show low-to-intermediate signal intensity

  • Edema, strain, or inflammation appears with bright signal intensity

STIR (Short Tau Inversion Recovery):

  • Normal muscle shows low-to-intermediate signal

  • Inflammatory, infectious, or traumatic changes appear bright

Proton Density Fat-Saturated (PD FS):

  • Muscles appear low-to-intermediate signal

  • Strain, tear, infection, or tumor infiltration appears as bright hyperintense areas

T1 Fat-Sat Post-Contrast:

  • Normal muscle shows mild uniform enhancement

  • Infection or inflammation shows heterogeneous enhancement

  • Abscess shows rim enhancement with non-enhancing center

  • Tumors demonstrate nodular or irregular enhancement

CT Appearance

Non-Contrast CT:

  • Muscles appear as symmetrical soft tissue densities along posterior spine

  • Fatty streaks visible in chronic atrophy

  • Abscesses or hematomas appear as hypo- or hyperdense lesions depending on content

Post-Contrast CT:

  • Normal muscle shows mild homogeneous enhancement

  • Infections, tumors, or inflammatory lesions show heterogeneous enhancement

  • Abscesses: peripheral rim enhancement with central low density

  • Fat stranding may indicate inflammation

MRI image

Erector spinae muscles mri axial image

MRI image

Erector spinae muscles mri coronal image

CT image

Erector spinae muscles ct axial image