The lumbar vertebrae are, in human anatomy, the five

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

between the

rib cage The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a sem ...

and the pelvis. They are the largest segments of the

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...

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.

Human anatomy

General characteristics

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 The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

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.'' Gray's Anatomy'' (1918), see infobox

Arch

The

pedicle Pedicle or pedicel may refer to: Human anatomy *Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures ...

s are very strong, directed backward from the upper part of the vertebral body; consequently, the inferior vertebral notches are of considerable depth. The pedicles change in morphology from the upper lumbar to the lower lumbar. They increase in

sagittal The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divi ...

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 Bone cements have been used very successfully to anchor artificial joints (hip joints, knee joints, shoulder and elbow joints) for more than half a century. Artificial joints (referred to as prostheses) are anchored with bone cement. The bone ce ...

as with

kyphoplasty Vertebral augmentation, including vertebroplasty and kyphoplasty, refers to similar percutaneous spinal procedures in which bone cement is injected through a small hole in the skin into a fractured vertebra in order to relieve back pain caused ...

or vertebroplasty. The laminae are broad, short, and strong. 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 In a typical vertebra, the vertebral foramen is the foramen (opening) formed by the anterior segment (the body), and the posterior part, the vertebral arch. The vertebral foramen begins at cervical vertebra #1 (C1 or atlas) and continues inferio ...

within the arch is triangular, larger than the

thoracic 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 ...

, but smaller than in the cervical vertebrae.

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. 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. 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. Three portions or ''tubercles'' can be noticed in a transverse process of a lower lumbar vertebrae: the lateral or ''costiform process'', the ''

mammillary process The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

'', and the ''

accessory process The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

''.Postacchini, Franco (1999) ''Lumbar Disc Herniation'
p.19
/ref> 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. 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.

First and fifth lumbar vertebrae

The first lumbar vertebra is level with the anterior end of the

ninth rib The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi ...

. This level is also called the important

transpyloric plane The transpyloric plane, also known as Addison's plane, is an imaginary horizontal plane, located halfway between the suprasternal notch of the manubrium and the upper border of the symphysis pubis at the level of the first lumbar vertebrae, L1. It ...

, since the

pylorus The pylorus ( or ), or pyloric part, connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pylori ...

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 The filum terminale ("terminal thread") is a delicate strand of fibrous tissue, about 20 cm in length, proceeding downward from the apex of the conus medullaris. It is one of the modifications of pia mater. It gives longitudinal support to th ...

, 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. The fifth lumbar vertebra is by far the most common site of

spondylolysis Spondylolysis is a defect or stress fracture in the pars interarticularis of the vertebral arch. The vast majority of cases occur in the lower lumbar vertebrae (L5), but spondylolysis may also occur in the cervical vertebrae.Dubousset, J. Trea ...

and

spondylolisthesis Spondylolisthesis is the displacement of one spinal vertebra compared to another. While some medical dictionaries define spondylolisthesis specifically as the forward or anterior displacement of a vertebra over the vertebra inferior to it (or t ...

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

Congenital anomalies

Congenital vertebral anomalies can cause compression of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...

by deforming the vertebral canal or causing instability. File:Lumbarization of S1.jpg, Lumbarization of sacral vertebra 1, seen as 6 vertebrae that do not connect to

ribs The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

. File:Sacralization of the fifth lumbar vertebra.jpg, Sacralization of the L5 vertebra is seen at the lower right of the image. File:Blockwirbel CT VR frontal.jpg, Congenital block vertebra of the lumbar spine. CT volume rendering.

Other animals

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 ''Nacholapithecus kerioi'' was an ape that lived 14-15 million years ago during the Middle Miocene. Fossils have been found in the Nachola formation in northern Kenya. The only member of the genus ''Nacholapithecus'', it is thought to be a key g ...

'' (a

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

hominoid with six lumbar vertebrae and no tail) are similar to those of early ''

Australopithecus ''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Austral ...

'' 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. The limited number of lumbar vertebrae in chimpanzees and

gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...

s result in an inability to lordose (curve) their lumbar spines, in contrast to the spines of

Old World monkey Old World monkey is the common English name for a family of primates known taxonomically as the Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons ...

s and ''Nacholapithecus'' and ''

Proconsul A proconsul was an official of ancient Rome who acted on behalf of a consul. A proconsul was typically a former consul. The term is also used in recent history for officials with delegated authority. In the Roman Republic, military command, or ...

'', which suggests that the last common ancestor was not "short-backed" as previously believed.

Additional images

MRI

File:SAGITTAL-FRFSE-T2 MRI.jpg, MRI lumbar spine with degeneration (sagittal T2 FRFSE) File:SAGITTAL-FSE T1 MRI.jpg, MRI lumbar spine with degeneration (sagittal T1 FSE) File:SAGITTAL-FAST-STIR-MRI.jpg, MRI lumbar spine with degeneration (sagittal FAST STIR) File:SAGITTAL-FRFSE-T2 MRI.ogg, MRI lumbar spine pre-hemilaminectomy (sagittal T2 FRFSE) File:SAGITTAL-FSE T1 MRI.ogg, MRI lumbar spine pre-hemilaminectomy (sagittal T1 FSE) File:SAGITTAL-FAST-STIR MRI.ogg, MRI lumbar spine pre-hemilaminectomy (sagittal FAST STIR) File:SAG.-T2-FRFSE-L-SPINE.ogg, MRI lumbar spine post-hemilaminectomy (sagittal T2 FRFSE) File:SAG.-T1-FSE-L-SPINE.ogg, MRI lumbar spine post-hemilaminectomy (sagittal T1 FSE) File:SAG.-T1-FSE-FS-L-SPINE-C+.ogg, Contrast MRI lumbar spine post-hemilaminectomy (sagittal T1 FSE FS)

Illustrations

File:Human lumbar vertebra.stl, 3D image of a lumbar vertebra File:Lumbar vertebrae animation.gif, Position of lumbar vertebrae (shown in red). Animation. File:Lumbar vertebrae animation4.gif, Same as the left. Bones around the lumbar vertebrae are shown as semi-transparent. File:Lumbar vertebrae - close-up - animation2.gif, Shape of lumbar vertebrae (shown in blue and yellow). Animation. File:Gray_111_-_Vertebral_column-coloured.png, Vertebral column. File:Gray430.png, Muscles of the iliac and anterior femoral regions. First lumbar vertebra second highest vertebra seen. File:Orientation.PNG, Orientation of vertebral column on surface. T3 is at level of medial part of spine of scapula. T7 is at inferior angle of the scapula. L4 is at highest point of

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the poster ...

. S2 is at the level of

posterior superior iliac spine The posterior border of the ala, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. The posterior superior iliac spine serves for the attachme ...

. Furthermore, C7 is easily localized as a prominence at the lower part of the neck.Anatomy Compendium (Godfried Roomans and Anca Dragomir) File:Illu vertebral column.svg, Vertebral column File:Blausen 0618 LumbarSpine.png, Illustration highlighting lumbar spine. File:Gray92.png, A lumbar vertebra seen from the side File:Gray106.png, Ossification of lumbar vertebrae

References

External links

* * {{DEFAULTSORT:Lumbar Vertebrae Bones of the thorax Bones of the vertebral column