Lumbar vertebrae

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Lumbar vertebrae
Lumbar vertebrae anterior.png
Position of human lumbar vertebrae (shown in red). It consists of 5 bones, from the top down, L1, L2, L3, L4 and L5.
Lumber vertebra 1 close-up superior surface animation.gif
Animation of L1
Details
Insertions Psoas major muscle
Nerve Lumbar nerves
Identifiers
Latin vertebrae lumbales
MeSH D008159
TA98 A02.2.04.001
TA2 1068
FMA 9921
Anatomical terms of bone

The lumbar vertebrae are located between the thoracic vertebrae and pelvis. They form the lower part of the human back in humans, and the tail end of the back in quadrupeds. In humans, there are five lumbar vertebrae. The term is used to describe the anatomy of humans and quadrupeds, such as horses, pigs, or cattle. These bones are found in particular cuts of meat, including tenderloin or sirloin steak.

Contents

Human anatomy

In human anatomy, the five vertebrae are between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse process (since it is only found in the cervical region) and by the absence of facets on the sides of the body (as found only in the thoracic region). They are designated L1 to L5, starting at the top. The lumbar vertebrae help support the weight of the body, and permit movement.

General characteristics

Lumbar vertebrae Lumbar vertebrae.jpg
Lumbar vertebrae

The adjacent figure depicts the general characteristics of the first through fourth lumbar vertebrae. The fifth vertebra contains certain peculiarities, which are detailed below.

As with other vertebrae, each lumbar vertebra consists of a vertebral body and a vertebral arch. The vertebral arch, consisting of a pair of pedicles and a pair of laminae, encloses the vertebral foramen (opening) and supports seven processes.

Body

The vertebral body of each lumbar vertebra is kidney shaped, wider from side to side than from front to back, and a little thicker in front than in back. It is flattened or slightly concave above and below, concave behind, and deeply constricted in front and at the sides. [1]

Arch

The pedicles are very strong, directed backward from the upper part of the vertebral body; consequently, the inferior vertebral notches are of considerable depth. [1] The pedicles change in morphology from the upper lumbar to the lower lumbar. They increase in sagittal width from 9 mm to up to 18 mm at L5. They increase in angulation in the axial plane from 10 degrees to 20 degrees by L5. The pedicle is sometimes used as a portal of entrance into the vertebral body for fixation with pedicle screws or for placement of bone cement as with kyphoplasty or vertebroplasty.

The laminae are broad, short, and strong. [1] They form the posterior portion of the vertebral arch. In the upper lumbar region the lamina are taller than wide but in the lower lumbar vertebra the lamina are wider than tall. The lamina connects the spinous process to the pedicles.

The vertebral foramen within the arch is triangular, larger than the thoracic vertebrae, but smaller than in the cervical vertebrae. [1]

Processes

The spinous process is thick, broad, and somewhat quadrilateral; it projects backward and ends in a rough, uneven border, thickest below where it is occasionally notched. [1]

The superior and inferior articular processes are well-defined, projecting respectively upward and downward from the junctions of pedicles and laminae. The facets on the superior processes are concave, and look backward and medialward; those on the inferior are convex, and are directed forward and lateralward. The former are wider apart than the latter since in the articulated column, the inferior articular processes are embraced by the superior processes of the subjacent vertebra. [1]

The transverse processes are long and slender. They are horizontal in the upper three lumbar vertebrae and incline a little upward in the lower two. In the upper three vertebrae they arise from the junctions of the pedicles and laminae, but in the lower two they are set farther forward and spring from the pedicles and posterior parts of the vertebral bodies. They are situated in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs. [1]

Three portions or tubercles can be noticed in a transverse process of a lower lumbar vertebrae: the lateral or costiform process, the mammillary process, and the accessory process. [2] The costiform is lateral, the mammillary is superior (cranial), and the accessory is inferior (caudal). The mammillary is connected in the lumbar region with the back part of the superior articular process.[ clarification needed ] The accessory process is situated at the back part of the base of the transverse process. The tallest and thickest costiform process is usually that of L5. [2]

First and fifth lumbar vertebrae

The fifth lumbar vertebra from above Gray94.png
The fifth lumbar vertebra from above

The first lumbar vertebra is level with the anterior end of the ninth rib. This level is also called the important transpyloric plane, since the pylorus of the stomach is at this level. Other important structures are also located at this level, they include; fundus of the gall bladder, celiac trunk, superior mesenteric artery, termination of spinal cord, beginning of filum terminale, renal vessels, middle suprarenal arteries, and hila of kidneys.

The fifth lumbar vertebra is characterized by its body being much deeper in front than behind, which accords with the prominence of the sacrovertebral articulation; by the smaller size of its spinous process; by the wide interval between the inferior articular processes, and by the thickness of its transverse processes, which spring from the body as well as from the pedicles. [1] The fifth lumbar vertebra is by far the most common site of spondylolysis and spondylolisthesis. [3]

Most individuals have five lumbar vertebrae, while some have four or six. Lumbar disorders that normally affect L5 will affect L4 or L6 in these latter individuals.

Segmental movements

The range of segmental movements in a single segment is difficult to measure clinically, not only because of variations between individuals, but also because it is age and sex dependent. Furthermore, flexion and extension in the lumbal spine is the product of a combination of rotation and translation in the sagittal plane between each vertebra. [4]

Ranges of segmental movements in the lumbar spine (White and Punjabi, 1990) are (in degrees): [5]

 L1-L2L2-L3L3-L4L4-L5L5-S1
Flexion/
Extension
12° 14°15°16°17°
Lateral
flexion
Axial
rotation

Congenital anomalies

Congenital vertebral anomalies can cause compression of the spinal cord by deforming the vertebral canal or causing instability.

Other apes

African apes have three and four lumbar vertebrae, (bonobos have longer spines with an additional vertebra) and humans normally five. This difference, and because the lumbar spines of the extinct Nacholapithecus (a Miocene hominoid with six lumbar vertebrae and no tail) are similar to those of early Australopithecus and early Homo, it is assumed that the chimpanzee–human last common ancestor also had a long vertebral column with a long lumbar region and that the reduction in the number of lumbar vertebrae evolved independently in each ape clade. [6] The limited number of lumbar vertebrae in chimpanzees and gorillas result in an inability to lordose (curve) their lumbar spines, in contrast to the spines of Old World monkeys and Nacholapithecus and Proconsul , which suggests that the last common ancestor was not "short-backed" as previously believed. [7]

Additional images

MRI

Illustrations

See also

Related Research Articles

<span class="mw-page-title-main">Rib</span> Long bone in vertebrates that protects vital respiratory and cardiovascular organs

In vertebrate anatomy, ribs are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the thoracic cavity. They serve to protect the lungs, heart, and other vital organs of the thorax. In some animals, especially snakes, ribs may provide support and protection for the entire body.

<span class="mw-page-title-main">Atlas (anatomy)</span> First cervical vertebra of the spine which supports the skull

In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck.

<span class="mw-page-title-main">Sacrum</span> Bone of the spine

The sacrum, in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1–S5) between ages 18 and 30.

<span class="mw-page-title-main">Spinal nerve</span> Nerve that carries signals between the spinal cord and the body

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.

<span class="mw-page-title-main">Axis (anatomy)</span> Second cervical vertebra of the spine

In anatomy, the axis is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests. The spinal cord passes through the axis.

<span class="mw-page-title-main">Laminectomy</span> Surgical removal of a lamina

A laminectomy is a surgical procedure that removes a portion of a vertebra called the lamina, which is the roof of the spinal canal. It is a major spine operation with residual scar tissue and may result in postlaminectomy syndrome. Depending on the problem, more conservative treatments may be viable.

<span class="mw-page-title-main">Cervical vertebrae</span> Vertebrae of the neck

In tetrapods, cervical vertebrae are the vertebrae of the neck, immediately below the skull. Truncal vertebrae lie caudal of cervical vertebrae. In sauropsid species, the cervical vertebrae bear cervical ribs. In lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes. Most mammals have seven cervical vertebrae, with the only three known exceptions being the manatee with six, the two-toed sloth with five or six, and the three-toed sloth with nine.

<span class="mw-page-title-main">Thoracic vertebrae</span> Vertebrae between the cervical vertebrae and the lumbar vertebrae

In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical and lumbar vertebrae; they increase in size going towards the lumbar vertebrae, with the lower ones being much larger than the upper. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, as well as facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. By convention, the human thoracic vertebrae are numbered T1–T12, with the first one (T1) located closest to the skull and the others going down the spine toward the lumbar region.

<span class="mw-page-title-main">Process (anatomy)</span> Projection or outgrowth of tissue from a larger body

In anatomy, a process is a projection or outgrowth of tissue from a larger body. For instance, in a vertebra, a process may serve for muscle attachment and leverage, or to fit, with another vertebra. The word is also used at the microanatomic level, where cells can have processes such as cilia or pedicels. Depending on the tissue, processes may also be called by other terms, such as apophysis, tubercle, or protuberance.

<span class="mw-page-title-main">Multifidus muscle</span> Muscle in the back

The multifidusmuscle consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the vertebrae, from the sacrum to the axis. While very thin, the multifidus muscle plays an important role in stabilizing the joints within the spine. The multifidus is one of the transversospinales.

<span class="mw-page-title-main">Erector spinae muscles</span> Human muscle group

The erector spinae or spinal erectors is a set of muscles that straighten and rotate the back. The spinal erectors work together with the glutes to maintain stable posture standing or sitting.

<span class="mw-page-title-main">Thoracolumbar fascia</span> Anatomical feature

The thoracolumbar fascia is a complex, multilayer arrangement of fascial and aponeurotic layers forming a separation between the paraspinal muscles on one side, and the muscles of the posterior abdominal wall on the other. It spans the length of the back, extending between the neck superiorly and the sacrum inferiorly. It entails the fasciae and aponeuroses of the latissimus dorsi muscle, serratus posterior inferior muscle, abdominal internal oblique muscle, and transverse abdominal muscle.

<span class="mw-page-title-main">Iliocostalis</span>

Iliocostalis muscle is the muscle immediately lateral to the longissimus that is the nearest to the furrow that separates the epaxial muscles from the hypaxial. It lies very deep to the fleshy portion of the serratus posterior muscle. It laterally flexes the vertebral column to the same side.

<span class="mw-page-title-main">Ligamenta flava</span> Ligaments connecting the laminae of adjacent vertebrae

The ligamenta flava are a series of ligaments that connect the ventral parts of the laminae of adjacent vertebrae. They help to preserve upright posture, preventing hyperflexion, and ensuring that the vertebral column straightens after flexion. Hypertrophy can cause spinal stenosis.

<span class="mw-page-title-main">Articular process</span> Projections of the vertebra

The articular process or zygapophysis of a vertebra is a projection of the vertebra that serves the purpose of fitting with an adjacent vertebra. The actual region of contact is called the articular facet.

<span class="mw-page-title-main">Iliolumbar ligament</span>

The iliolumbar ligament is a strong ligament which attaches medially to the transverse process of the 5th lumbar vertebra, and laterally to back of the inner lip of the iliac crest.

<span class="mw-page-title-main">Laminotomy</span> Surgical procedure

A laminotomy is an orthopaedic neurosurgical procedure that removes part of the lamina of a vertebral arch in order to relieve pressure in the vertebral canal. A laminotomy is less invasive than conventional vertebral column surgery techniques, such as laminectomy because it leaves more ligaments and muscles attached to the spinous process intact and it requires removing less bone from the vertebra. As a result, laminotomies typically have a faster recovery time and result in fewer postoperative complications. Nevertheless, possible risks can occur during or after the procedure like infection, hematomas, and dural tears. Laminotomies are commonly performed as treatment for lumbar spinal stenosis and herniated disks. MRI and CT scans are often used pre- and post surgery to determine if the procedure was successful.

<span class="mw-page-title-main">Outline of human anatomy</span> Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

<span class="mw-page-title-main">Vertebral column</span> Bony structure found in vertebrates

The vertebral column, also known as the spinal column, spine or backbone, is the core part of the axial skeleton in vertebrate animals. The vertebral column is the defining and eponymous characteristic of the vertebrate endoskeleton, where the notochord found in all chordates has been replaced by a segmented series of mineralized irregular bones called vertebrae, separated by fibrocartilaginous intervertebral discs. The dorsal portion of the vertebral column houses the spinal canal, an elongated cavity formed by alignment of the vertebral neural arches that encloses and protects the spinal cord, with spinal nerves exiting via the intervertebral foramina to innervate each body segments.

<span class="mw-page-title-main">Vertebra</span> Bone in the vertebral column

Each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal segment and the particular species.

References

PD-icon.svgThis article incorporates text in the public domain from page 104 of the 20th edition of Gray's Anatomy (1918)

  1. 1 2 3 4 5 6 7 8 Gray's Anatomy (1918), see infobox
  2. 1 2 Postacchini, Franco (1999) Lumbar Disc Herniation p.19
  3. Eizenberg, N. et al. (2008). General Anatomy: Principles and Applications, p. 17.
  4. Hansen; et al. (2006). "Anatomy and Biomechanics of the Back Muscles in the Lumbar Spine With Reference to Biomechanical Modeling". Spine. 31 (17). Medscape: 1888–99. doi:10.1097/01.brs.0000229232.66090.58. PMID   16924205. S2CID   43352264. Archived from the original on November 14, 2010.
  5. Hansen; et al. (2006). "Ranges of Segmental Motion for the Lumbar Spine". Medscape. Archived from the original on July 5, 2015.
  6. McCollum, MA; Rosenman, BA; Suwa, G; Meindl, RS; Lovejoy, CO (March 15, 2010). "The vertebral formula of the last common ancestor of African apes and humans". Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 314 (2): 123–34. doi:10.1002/jez.b.21316. PMID   19688850. (Abstract)
  7. Lovejoy, C. Owen; McCollum, Melanie A. (October 27, 2010). "Spinopelvic pathways to bipedality: why no hominids ever relied on a bent-hip-bent-knee gait". Philos Trans R Soc Lond B Biol Sci. 365 (1556): 3289–99. doi:10.1098/rstb.2010.0112. PMC   2981964 . PMID   20855303. (Introduction)
  8. Anatomy Compendium (Godfried Roomans and Anca Dragomir)