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L (Lumbar spine)

The lumbar spine (L-spine) consists of five large vertebrae (L1–L5) forming the lower part of the vertebral column between the thoracic spine and the sacrum. It is designed to provide structural support, flexibility, and weight transmission from the upper body to the pelvis and lower limbs.

The lumbar spine encloses the lower spinal cord (upper levels), cauda equina, and major nerve roots and is a central region of interest in musculoskeletal and neuroimaging.

Synonyms

  • Lumbar vertebral column

  • Lower back spine

Location

  • Located between the thoracic spine and the sacrum

  • Extends from the T12–L1 intervertebral disc superiorly to the L5–S1 disc inferiorly

  • Forms the lumbar lordosis

  • Posterior to the abdominal cavity

  • Anterior to the paraspinal muscles and skin of the lower back

Anatomical components

  • Lumbar vertebrae (L1–L5):

    • Large vertebral bodies

    • Short, thick pedicles

    • Broad laminae

  • Intervertebral discs:

    • Nucleus pulposus

    • Annulus fibrosus

  • Posterior elements:

    • Spinous processes

    • Transverse processes

    • Articular facets

  • Spinal canal contents:

    • Cauda equina

    • Filum terminale

    • Dural sac

  • Supporting ligaments:

    • Anterior longitudinal ligament

    • Posterior longitudinal ligament

    • Ligamentum flavum

    • Interspinous and supraspinous ligaments

Relations

Anteriorly:

  • Abdominal aorta and inferior vena cava

  • Retroperitoneal organs

Posteriorly:

  • Paraspinal muscles (erector spinae, multifidus)

  • Thoracolumbar fascia

Laterally:

  • Psoas major muscles

  • Quadratus lumborum muscles

Inferiorly:

  • Sacrum and lumbosacral junction (L5–S1)

Superiorly:

  • Thoracolumbar junction (T12–L1)

X-ray appearance

Plain radiographs (AP and lateral views):

  • Vertebral bodies: Rectangular with increasing size caudally

  • Intervertebral disc spaces: Uniform height in normal alignment

  • Pedicles: Symmetric on AP view

  • Spinous processes: Midline alignment

  • Lumbar lordosis: Well-formed curvature on lateral view

  • Facet joints: Oblique orientation, best seen on oblique views

CT appearance (pre-contrast)

Axial and sagittal reconstructions:

  • Cortical bone: High-density outer shell of vertebral bodies and posterior elements

  • Trabecular bone: Lower density central marrow space

  • Pedicles and laminae: Thick, well-defined osseous structures

  • Facet joints: Clearly visualized articular surfaces

  • Spinal canal: Osseous boundaries well delineated

  • Intervertebral discs: Soft-tissue density between vertebral bodies

  • Neural foramina: Bony margins sharply defined

MRI appearance

T1-weighted images:

  • Vertebral marrow: High signal intensity (fatty marrow dominant in adults)

  • Intervertebral discs: Intermediate to low signal

  • Spinal cord / cauda equina: Intermediate signal

  • CSF: Low signal

  • Paraspinal fat: High signal

T2-weighted images:

  • CSF: High signal

  • Intervertebral discs: High signal in the nucleus pulposus

  • Spinal cord / cauda equina: Intermediate signal

  • Vertebral marrow: Intermediate signal

  • Facet joints: Thin high-signal joint fluid may be seen

STIR:

  • Fat suppression: Suppresses vertebral marrow fat signal

  • Vertebral bodies: Low signal background

  • Intervertebral discs: Intermediate signal

  • CSF: High signal

  • Ligaments and soft tissues: Low signal

MRI image

Lumbar spine mri axial anatomy Location and Imaging Appearance -img-00000-00000

MRI image

Lumbar spine mri coronal anatomy Location and Imaging Appearance -img-00000-00000

MRI image

Lumbar spine mri sagittal anatomy Location and Imaging Appearance -img-00000-00000

CT images

Lumbar spine CT SAG anatomy Location and Imaging Appearance -img-00000-00000

X Ray image

x ray l spine lat-img-00000-00000 (1)