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Lumbar vertebrae: want to learn more about it?

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Lumbar vertebrae

The lumbar vertebrae are located at the bottom section of the vertebral column, inferior to the rib cage and superior to the pelvis and sacrum. Since these vertebrae are most largely responsible for bearing the weight of the upper body (and permitting movement), they are logically also the largest segments of the vertebral column. These vertebrae are characterized by the absence of the foramen transversarium within the transverse process, and by the absence of facets on the sides of the body.

Anatomy

General characteristics

There are 5 lumbar vertebrae (denoted as L1-L5) found in adult humans, and they are situated beneath the thoracic vertebrae, They are the largest, in terms of size, out of all the vertebrae because the lumbar vertebrae must be able to support the weight of the body when a person is standing due to the effects of gravity.

Anatomy of the typical vertebra (diagram)

To summarize, the main anatomical components of a lumbar vertebra are:

  • Vertebral body
  • Vertebral arch
  • Spinous process
  • Pedicles and laminae
  • Vertebral foramen
  • Superior and inferior articular processes/facets
  • Transverse processes

Distinguishing features of the lumbar vertebrae include a thick and stout vertebral body, a blunt, quadrilateral spinous process for the attachment of strong lumbar muscles, and articular processes that are oriented differently than those found on the other vertebrae. The vertebral body is large, wider laterally compared to longitudinally, and thicker in the front than in the back. It is also flattened or slightly concave superiorly and inferiorly, concave behind, and deeply restricted at the front and laterally.

Lumbar vertebrae from the human cadaver: Notice how lumbar vertebrae have massive bodies to bear the body weight.

Each lumbar vertebra has a vertebral body and a vertebral arch. The vertebral arch consists of a pair of pedicles and a pair of laminae, which encircles the vertebral foramen that ultimately supports 7 processes. The pedicles are very strong and are directed backwards from the upper part of the vertebral body. As a result, the inferior vertebral notches have considerable depth. The pedicles also change in morphology from L1 to L5, increasing in width from 9 mm up to 18 mm at L5. The angle in the axial plane also increases from 10 to 20 degrees from L1 to L5.

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The laminae are strong, broad, and short in morphology, and form the posterior portion of the vertebral arch. The upper lumbar laminae regions are taller instead of wider, whereas the lower lumbar laminae regions are wider instead of tall. Laminae connect the spinous process to the pedicles.

The vertebral foramen is triangular-shaped within the arch, and larger in size than in the thoracic vertebrae, but smaller than in the cervical vertebrae. The superior and inferior articular processes are well-defined, and project upward and downward from the junctions of pedicles and laminae, respectively. The superior processes are concave and face medially (like when the palms of the hands are facing each other when about to clap), whereas the inferior processes are convex and face lateralward towards the superior processes of the next vertebra. This anatomical conformation allows for resistance against the twisting of the lower spine.

Transverse processes are long and slender, with changing morphology from L1 to L5. These processes are horizontal in L1-L3, and incline a little upward in L4-L5. In L1-L3, the transverse processes arise from the junctions of the pedicles and laminae, but in L4-L5, they arise from the pedicles and posterior portions of the vertebral bodies since they are set farther forward. The transverse processes are positioned in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs.

Specific lumbar vertebrae

  • First lumbar vertebrae (L1) - L1 is roughly inline with the anterior end of the 9th rib at a level called the transpyloric plane (since the pylorus of the stomach is found at this level).
  • Fifth lumbar vertebrae (L5) - L5 is significantly different in morphology, with its body being much deeper in front than behind, which allows for articulation with the sacrovertebral prominences. The spinous process is smaller, there is a wider interval between the inferior articular processes, and the transverse processes are thicker and spring from the body as well as the pedicles.

Nerves

The spinal cord extends down to the L2 vertebra. Below the L2 level, the spinal canal surrounds a bundle of nerves known as the cauda equina (“horse’s tail”), which reaches down into the lower limbs and pelvic organs.

Cauda equina in a cadaver: This nerve bundle contains spinal nerves L2-L5, S1-S5 and Co.

Muscles affecting lumbar vertebrae function

  • Longissimus muscle - This is a long muscle with a lumbar vertebral origin at the transverse processes and spinous processes. The longissmus muscle can extend the spine upon bilateral contraction, and unilateral contraction can bend the spine laterally to the same side.
  • Spinalis muscle - This is a long muscle that is part of the erector spinae bundle of muscles and tendons, which helps the spine with movement and also helps in maintaining posture and staying erect when standing.
  • Multifidus muscle - This is a long muscle that traverses the length of the back and functions in stabilizing and rotating the lumbar spine.
  • Intertransversarii muscle (mediales lumborum and laterales lumborum- This muscle is specifically found from L1-L5. It bilaterally stabilizes and extends the lumbar spine and unilaterally bends the lumbar spine laterally to the same side.
  • Psoas major - This muscle helps bend the trunk laterally, and raises the trunk from the supine position bilaterally.

Lumbar vertebrae: want to learn more about it?

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