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Lumbar vertebrae

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Structure and location of the lumbar spine and features of the lumbar vertebrae.

The lumbar spine is located in the lower half of the vertebral column, inferior to the thoracic vertebrae/rib cage and superior to the pelvis and sacrum.

The lumbar vertebrae are five in number and desginated as vertebrae L1-L5. They are primarily responsible for bearing the weight of the upper body (and permitting movement) and consequently represent the largest individual segments of the vertebral column. They are characterized by their relatively large vertebral bodies as well as lack of foramina transversaria and costal facets.

Key facts about the lumbar vertebrae
Definition - Five large weight bearing vertebrae located between the thoracic vertebrae and sacrum; large in size;
- Lack foramina transversaria (found in cervical vertebrae) and costal facets (found in thoracic vertebrae)
Vertebral body Large and wide, kidney shaped, thicker anteriorly vs. posteriorly
Vertebral foramen Triangular, larger than that in thoracic vertebrae, smaller than in cervical region
Transverse processes Long and slender, bears an accessory process on posterior aspect
Spinous process Short and blunt, project almost horizontally, hatchet shape
Superior/inferior articular processes Superior articular facets face medially, inferior articular facets face laterally; superior articular processes bear a mammillary process on their posterior aspect
Movements Flexion and extension, some lateral flexion, limited/restricted rotation
Contents
  1. Anatomy
    1. Vertebral body
    2. Vertebral arch
    3. Transverse process
    4. Accessory process
    5. Articular processes/facets
    6. Mammillary process
    7. Spinous process
    8. Specific lumbar vertebrae
  2. Muscles affecting lumbar vertebrae function
  3. Clinical notes
    1. Lumbarization
    2. Sacralization
    3. Lumbar scoliosis
    4. Lumbar lordosis
    5. Spondylolysis and spondylolisthesis
    6. Disk herniation
  4. Sources
+ Show all

Anatomy

They lumbar vertebrae are the largest, in terms of size, out of all the vertebrae due to their role in supporting the weight of the body when a person is standing due to the effects of gravity. 

To refresh our memories, the main anatomical components of all vertebrae are: the vertebral body, vertebral arch (pedicles and laminae), vertebral foramen, superior and inferior articular processes/facets and transverse processes.

Vertebral body

The lumbar vertebrae are perhaps most easily defined by their stout and think vertebral bodies; they are relatively large, wider laterally compared to anteroposteriorly and thicker in its anterior half compared to posterior (which contributes to the lumbar lordosis). Their intervertebral surfaces are somewhat flattened or slightly concave superiorly and inferiorly, concave behind and deeply restricted at the front and laterally.

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

Want to learn more about the vertebral column? Our spine quizzes and labeled diagrams are the best way to learn and consolidate knowledge at the same time. 

Vertebral arch

The vertebral arches of lumbar vertebrae consist of paired of pedicles and laminae which encircle the vertebral foramen and ultimately support seven main processes. They are small in appearance relative to the size of the vertebral bodies. The pedicles are stout and strong, projecting posteriorly from the upper part of the vertebral body. As a result, the inferior vertebral notches have considerable depth compared to their superior counterparts. The pedicles also change in morphology from vertebrae L1 to L5, increasing in width from 9 mm up to 18 mm. The angle of orientation in the axial plane also increases from 10 to 20 degrees from vertebrae L1 to L5.
The laminae are strong, broad and short in morphology and form the posterior portion of the vertebral arch. The upper lumbar laminae are taller instead of wider, whereas the lower lumbar laminae are wider instead of tall. The laminae merge together at the midline to complete the posterior part of the vertebral arch, providing a base for a spinous process.
The vertebral foramen enclosed by the vertebral arch is triangular in appearance, smaller than that typically found among the cervical vertebrae but larger than those typical of the thoracic spine.

Transverse process

Transverse processes of lumbar vertebrae are long and slender compared to their thoracic counterparts, with changing morphology from vertebrae L1 to L5. These processes are horizontal in L1-L3 and incline slightly 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 anterior to the articular processes instead of behind them as in the thoracic vertebrae.

In the lumbar vertebrae, the costal element of each transverse process (pleurapophysis or costal process) occupies most of the anterior and lateral aspect of the transverse process, with only the root and parts of the posterior aspect (accessory process, see below) originating as ‘true’ transverse process elements (diapophysis).

Accessory process

Each lumbar transverse process usually bears a small tubercle along its posterior proximal aspect, known as an accessory process. They serve as attachment sites for the intertransversarii and longissimus muscles (see below).

Articular processes/facets

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 laterally towards the superior articular facets of the vertebra below, forming zygapophyseal (facet) joints. This anatomical conformation allows for a good degree of flexion/extension, but limited twisting/rotation of the lumbar spine.

When viewed posteriorly, the superior and inferior articular processes of vertebrae L1 and L2 collectively form a inverted vertically elongated trapezoid shape; those of vertebrae L3 and L4 form a square, while those of vertebra L5 form a horizontally elongated trapezoid.

Mammillary process

Mammillary processes are small tubercles located on the posterior aspect of the superior articular processes of lumbar vertebrae (and sometimes vertebra T12). They serve as attachment sites for the intertransversarii and multifidus muscles.

Spinous process

The spinous process is short, 'hatchet shaped' and blunt in appearance; it  projects almost horizontally from the posterior aspect of the vertebral arch. They are quadrilateral, hatchet shaped in appearance.

Specific lumbar vertebrae

  • First lumbar vertebrae (L1): smallest of the series and lies 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): is significantly different in morphology, with its body being much deeper anteriorly than posteriorly, contributing to the lumbosacral angle. The spinous process is smaller than higher lumbar vertebrae and there is a wider interval between the inferior articular processes, which face almost anteriorly rather than laterally. The transverse processes are substantially thicker and arise from the body as well as the pedicles.

Test your knowledge on the structures of the lumbar spine with our interactive quiz!

Muscles affecting lumbar vertebrae function

  • Longissimus muscle:  a long muscle with a lumbar vertebral attachment at the transverse processes and accessory processes. It extends the spine upon bilateral contraction and unilateral contraction can bend the spine laterally to the same side.
  • Spinalis muscle: a long muscle that is part of the erector spinae group. Its thoracic part attaches to the spinous processes of the upper lumbar vertebra (L1, L2), which helps the spine with movement and also helps in maintaining posture and staying erect (extension) when standing.
  • Multifidus muscle: a long muscle that traverses the length of the back and functions in stabilizing and contralateral rotation the spine. In the lumbar spine, the multifidus lumborum attaches to the mammillary processes extending superiorly to the spinous process of vertebrae two-five levels above.
  • Intertransversarii muscles (medial and lateral): the medial lumbar intertransversarii extend between the accessory processes of each vertebra L1-L4 to the mammillary process of the vertebra below. The lateral lumbar intertransversarii have attachments between the transverse and accessory processes of L1-L4 and the transverse process of the succeeding vertebra. They serve to bilaterally stabilizes the lumbar spine and assist in lateral flexion.
  • Psoas major: helps bend the trunk laterally and raises/flexes the trunk from the supine position bilaterally. It attaches to the transverse process of all lumbar vertebrae extending to the lesser trochanter of the femur.

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