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Interspinales lumborum muscle

The interspinales lumborum are small paired muscles of the deep intrinsic back group. They are positioned between the spinous processes of adjacent lumbar vertebrae and contribute to fine postural adjustments and stabilization of the lumbar spine. Although small, they play an important role in proprioception and segmental control of spinal movement. They are often grouped with other minor deep muscles such as the intertransversarii and rotatores.

Synonyms

  • Lumbar interspinales muscles

  • Interspinal muscles of lumbar spine

  • Small paired extensors of lumbar spine

Origin, Course, and Insertion

  • Origin: Arise from the superior surface of a lumbar spinous process

  • Course: Short vertical fibers pass directly upward between adjacent spinous processes

  • Insertion: Attach to the inferior surface of the spinous process immediately above

Relations

  • Anteriorly: Ligamentum flavum and vertebral laminae

  • Posteriorly: Thoracolumbar fascia and overlying erector spinae (multifidus)

  • Laterally: Intertransversarii muscles and lumbar transverse processes

  • Medially: Supraspinous ligament and spinous tips

Function

  • Extend the lumbar spine when acting bilaterally

  • Aid in fine-tuning posture and controlling intersegmental motion

  • Provide proprioceptive input for lumbar stabilization

  • Act synergistically with multifidus and erector spinae during extension

Clinical Significance

  • May undergo fatty atrophy or degeneration in chronic low back pain

  • Can be affected by lumbar instability, trauma, or surgery

  • Important in functional MRI and EMG studies of lumbar stability

  • Rarely involved as primary pain generators but may contribute to local tenderness

MRI Appearance

T1-weighted images:

  • Muscles show low-to-intermediate signal intensity

  • Fatty streaks or atrophy appear as bright signal between fibers

T2-weighted images:

  • Muscles show low-to-intermediate signal intensity

  • Acute strain, edema, or denervation shows bright hyperintensity

STIR (Short Tau Inversion Recovery):

  • Normal muscles appear dark to intermediate

  • Pathologic changes (edema, inflammation) appear bright

T1 Fat-Sat Post-Contrast:

  • Normal muscle shows mild, uniform enhancement

  • Pathologic muscle (myositis, abscess, tumor infiltration) shows focal or heterogeneous enhancement

3D T2 SPACE / CISS:

  • Muscles show intermediate signal intensity compared to muscle baseline

  • Surrounded by bright CSF in interlaminar spaces, providing contrast at spinous process level

CT Appearance

Non-Contrast CT:

  • Muscles appear as small soft tissue densities between adjacent spinous processes

  • Fatty infiltration appears as lower attenuation

  • May be difficult to distinguish without high-resolution images

Post-Contrast CT:

  • Muscles show mild homogeneous enhancement

  • Inflammatory or neoplastic involvement shows irregular or nodular enhancement

  • Chronic degeneration shows reduced bulk with fatty replacement

MRI image

Interspinales lumborum muscle MRI axial anatomy image-img-00000-00000

MRI image

Interspinales lumborum muscle MRI sagittal anatomy image-img-00000-00000

CT image

Interspinales lumborum muscle CT axial anatomy image-img-00000-00000