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Spinalis muscle

The spinalis muscle is the most medial subdivision of the erector spinae group, which also includes the longissimus and iliocostalis muscles. It lies adjacent to the spinous processes and extends longitudinally along the vertebral column. The spinalis is typically divided into three regions:

  • Spinalis thoracis → arises from the spinous processes of T11–L2 and inserts into the spinous processes of upper thoracic vertebrae (T1–T8).

  • Spinalis cervicis → arises from the spinous processes of C7–T2 and inserts into the spinous processes of C2–C4 (often small or variable).

  • Spinalis capitis → blends with the semispinalis capitis and is often indistinct.

Together, these muscles act as part of the deep intrinsic back muscles, primarily responsible for extension and stabilization of the spine.

Synonyms

  • Spinalis thoracis

  • Spinalis cervicis

  • Spinalis capitis

  • Medial erector spinae muscle

Function

  • Extends the vertebral column (bilateral contraction)

  • Contributes to lateral flexion of the spine (unilateral contraction)

  • Provides postural support and stabilization during standing and movement

Nerve Supply

  • Dorsal rami of spinal nerves at the corresponding vertebral levels

Arterial Supply

  • Dorsal branches of posterior intercostal arteries

  • Lumbar arteries

  • Occipital artery branches (for spinalis capitis region)

Venous Drainage

  • Corresponding veins mirror the arterial supply:

    • Posterior intercostal veins

    • Lumbar veins

    • Occipital venous plexus

MRI Appearance

T1-weighted images:

  • Normal muscle: intermediate signal intensity with fascicular pattern

  • Fatty infiltration/atrophy: high signal intensity

T2-weighted images:

  • Normal muscle: low-to-intermediate signal intensity

  • Edema, strain, or myositis: hyperintense changes

STIR:

  • Fat suppression highlights acute inflammation, trauma, or edema as bright hyperintensity

  • Very sensitive for paraspinal pathology

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal enhancement is mild and homogeneous

  • Pathological conditions (infection, neoplasm, myositis) show abnormal heterogeneous enhancement

MRI Non-Contrast 3D Imaging:

  • Provides 3D anatomical reconstruction of erector spinae group

  • Useful for pre-surgical mapping, tumor delineation, and scoliosis/spinal deformity evaluation

CT Appearance

Non-contrast CT:

  • Muscle appears as paraspinal soft tissue density adjacent to spinous processes

  • Chronic atrophy seen as volume loss and fat replacement

CT Post-Contrast:

  • Enhances abnormal processes such as infection, tumor infiltration, or abscess formation

  • Provides high-resolution evaluation of osseous landmarks with adjacent muscle involvement

MRI image

Spinalis muscle anatomy MRI axial image -img-00000-00000

CT image

Spinalis muscle anatomy CT axial image -img-00000-00000