First Lumbar Vertebra

Key Features & Anatomical Relations

The first lumbar vertebra (vertebra L1) is the smallest of the five lumbar vertebrae of the vertebral column. It is classified as an irregular bone and includes the following bony features:

- parts: vertebral body, laminae, pedicles, superior and inferior articular processes, and transverse and spinous processes;

- surfaces: superior and inferior intervertebral surfaces, superior and inferior annular epiphyses, and vertebral arch;

- landmarks: superior and inferior vertebral notches, mammillary and accessory processes, and superior and inferior articular facets.

More information regarding these and other bony features can be found in the Parts, Surfaces, and Landmarks tabs for this bone.

The first lumbar vertebra is located:

- superior to the second lumbar vertebra;

- inferior to the twelfth thoracic vertebra.

It articulates with the twelfth thoracic second lumbar vertebrae at the intervertebral symphyses and zygapophyseal joints.

Ossification

Ossification of all lumbar vertebrae occurs at ten ossification centers, these are found in the:

- vertebral body, which appears in utero during the second to fourth months;

- right and left halves of the vertebral arch, with one center found in each, which appear in utero during the third month;

- right and left transverse processes, with one center found in each, which appear during puberty;

- spinous process, which appears during puberty;

- superior and inferior annular epiphyses, with one center found in each, which appear during puberty;

- right and left mammillary processes, with one center found in each, which appear during early adolescence.

The ossification centers for the right and left halves of the vertebral arch fuse with each other during the first year after birth. The vertebral arch fuses with the vertebral body during the third year. The remaining centers fuse with the vertebral arch and body during early adulthood (Standring, 2016).

Variations

In some individuals:

- the first lumbar vertebra may have rudimentary ribs;

- the superior or inferior articular processes of lumbar vertebrae may occasionally present an accessory ossicle, known as an Oppenheimer ossicle (Tubbs, Shoja and Loukas, 2016).

Surface Anatomy

The spinous process of the first lumbar vertebra can be palpated, especially during flexion of the trunk.

List of Clinical Correlates

- Fracture

- Osteoporosis

- Spinal stenosis

- Scoliosis

- Spondylosis

- Spondylolisthesis

- Spondylolysis

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.

Tubbs, R. S., Shoja, M. M. and Loukas, M. (2016) Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. Wiley.