Osteology of Lumbar Vertebrae

Overview

• Lumbar vertebrae are weight-bearing vertebrae, more massive than thoracic vertebrae.
• Consist of five vertebrae: the first four are typical, the fifth is atypical.

Features of Lumbar Vertebrae

• Body: Massive, kidney-shaped (reniform).

  • Transverse diameter > anterior-posterior diameter.
  • Increases in size from the first to the fifth vertebra.
  • Larger than thoracic but smaller than cervical vertebrae.
  • Triangular shape.

• Vertebral Arch Components:

  • Pedicles: Short, strong, projecting backwards from the body's upper parts.
    • Inferior vertebral notches are deeper than superior ones.
  • Laminae: Short, thick, broad, directed posterior medially with minimal overlap.
  • Spine: Quadrilateral shape, projects backwards.
  • Transverse Processes: Thin, tapering, homologous to thoracic ribs.
    • Accessory process: Small, rough elevation on posterior inferior aspect.

• Articular Processes:

  • Superior Articular Processes:
    • Concave facets, project backward and medially.
    • Farther apart than inferior ones.
    • Mammillary process: Rough elevation on posterior borders.
  • Inferior Articular Processes:
    • Convex facets, face forward and laterally.
    • Closer together than superior ones.

Atypical Features of Fifth Lumbar Vertebra

• Transverse Processes:
  • Thick, short, pyramidal, attached to whole pedicle thickness.
  • Can encroach on body, turned upwards.
• Spine: Small, short, rounded, least substantial.
• Body: Largest among lumbar vertebrae.
  • Anterior height > posterior height, creating a lumbosacral angle (~120°).
• Articular Facets:
  • Superior facets look more backwards than medially.
  • Inferior facets look more forwards than laterally.
  • Distance between inferior processes ≥ superior processes.

Conditions Involving the Fifth Lumbar Vertebra

• Fusion with Sacrum:

  • Can be complete or incomplete.
  • L5 transverse process may articulate with sacrum's ala or ilium, compressing the L5 spinal nerve (5% incidence).

• Spondylolysis:

  • Separation of L5 body from vertebral arch on one side.
  • Usually involves interlocking with sacrum's articular processes.

• Spondylolisthesis:

  • Forward slipping of L5 over sacrum.
  • May involve separation of inferior processes, laminae, and spine.
  • Clinically presents as backache and sciatica.