The fifth lumbar vertebra is considered atypical because of its shape.

It is the largest of the five lumbar vertebrae. In contrast to the typical lumbar vertebrae, L5 also has a distinct transverse process.

Anterior features of the L5 include a large vertebral body, which is oval/kidney shaped in an axial view, and wedge-shaped in a sagittal view.

Posterior components and features of the L5 include:

Pedicles - project directly posteriorly
Transverse processes - with features distinguishing of L5: The transverse processes of the L5 are short, massive, somewhat cone-shaped. The base of the transverse process is attached from the pedicle to the lateral side of the vertebral body. Serves for attachment of iliolumbar ligaments (ligaments that connect the transverse processes to the pelvic bones).
Lamina - broad, thick, overlap minimally
Articular process - superior and inferior
Facet joints - obliquely oriented, cylindrical shaped
Superior articular facets - concave, faced posteromedially
Inferior articular facets - convex, faced anteriorly
Spinous process - single, short, thick, and roughly horizontal

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Atypical lumbar vertebra (L5)