Lumbar vertebrae
Encyclopedia
The lumbar vertebrae are the largest segments of the movable part of the vertebral column
, and 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. They are designated L1 to L5, starting at the top.
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
.
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 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. 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 connect the spinous process to the pedicles.
The vertebral foramen
within the arch is triangular, larger than in the thoracic vertebrae
, but smaller than in the cervical vertebrae
.
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.
Of the three tubercles noticed in connection with the transverse processes of the lower lumbar vertebrae, the superior one is connected in the lumbar region with the back part of the superior articular process, and is named the mammillary process
. The inferior is situated at the back part of the base of the transverse process, and is called the accessory process
.
Some individuals have four lumbar vertebrae, while others have six. Lumbar disorders that normally affect L5 will affect L4 or L6 in these individuals.
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.
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
and spondylolisthesis
.
Ranges of segmental movements in the lumbal spine (White and Panjabi, 1990) are (in degrees):
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
, and 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. They are designated L1 to L5, starting at the top.
General characteristics
These are 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
Process (anatomy)
In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...
.
Body
The vertebral body of each lumbar vertebra is large, 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.Arch
The pediclePedicle of vertebral arch
The pedicles are two short, thick processes, which project dorsally, one on either side, from the superior part of the vertebral body at the junction of its posterior and lateral surfaces. They connect the body of the spinal vertebra to the arch...
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 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 cement
Bone cements have been used very successfully to anchor artificial joints for more than half a century. Artificial joints are anchored with bone cement. The bone cement fills the free space between the prosthesis and the bone and plays the important role of an elastic zone...
as with kyphoplasty 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 connect the spinous process to the pedicles.
The vertebral foramen
Vertebral foramen
In a typical vertebra, the vertebral foramen is the foramen formed by the anterior segment , and the posterior part, the vertebral arch....
within the arch is triangular, larger than in the thoracic vertebrae
Thoracic vertebrae
In human anatomy, twelve thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. They are intermediate in size between those of the cervical and lumbar regions; they increase in size as one proceeds down the spine, the upper...
, but smaller than in the cervical vertebrae
Cervical vertebrae
In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...
.
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
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
with the ribs.
Of the three tubercles noticed in connection with the transverse processes of the lower lumbar vertebrae, the superior one is connected in the lumbar region with the back part of the superior articular process, and is named the mammillary process
Mammillary process
Of the three tubercles noticed in connection with the transverse processes of the lumbar vertebrae, the superior one is connected in the lumbar region with the back part of the superior articular process, and is named the mammillary process....
. The inferior is situated at the back part of the base of the transverse process, and is called the accessory process
Accessory process
Of the tubercles noticed in connection with the transverse processes of the lower lumbar vertebrae, the inferior is situated at the back part of the base of the transverse process, and is called the accessory process....
.
First to fifth lumbar vertebrae
The first lumbar vertebra is level with the anterior end of the ninth rib. This level is also called the important transpyloric plane
Transpyloric plane
An upper transverse line also known as Addison's Plane, is located halfway between the jugular notch and the upper border of the pubic symphysis; this indicates the margin of the transpyloric plane, which in most cases cuts through the pylorus, the tips of the ninth costal cartilages and the lower...
, since the pylorus
Pylorus
The pylorus is the region of the stomach that connects to the duodenum . It is divided into two parts:* the pyloric antrum, which connects to the body of the stomach.* the pyloric canal, which connects to the duodenum....
of the stomach is at this level.
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
Spondylolysis is a defect of a vertebra. More specifically it is defined as a defect in the pars interarticularis of the vertebral arch. The great majority of cases occur in the lowest of the lumbar vertebrae , but spondylolysis may also occur in the other lumbar vertebrae, as well as in the...
and spondylolisthesis
Spondylolisthesis
Spondylolisthesis describes the anterior or posterior displacement of a vertebra or the vertebral column in relation to the vertebrae below. It was first described in 1782 by Belgian obstetrician, Dr. Herbinaux. He reported a bony prominence anterior to the sacrum that obstructed the vagina of a...
.
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 gender 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 lumbal spine (White and Panjabi, 1990) are (in degrees):
| L1-L2 | L2-L3 | L3-L4 | L4-L5 | L5-S1 | |
| Flexion/ Extension |
12 | 14 | 15 | 16 | 17 |
| Lateral flexion |
6 | 6 | 8 | 6 | 3 |
| Axial rotation |
2 | 2 | 2 | 2 | 1 |
See also
- Sacralization of the l5
- Bertolotti's syndromeBertolotti's syndromeBertolotti's syndrome is a form of back pain associated with lumbosacral transitional vertebrae. It can be treated surgically with posterolateral fusion or resection of the transitional articulation. Non surgical treatments include steriod injections in the lower back or radiofrequency sensory...
- Lumbarization of the s1
- Spinal disc herniationSpinal disc herniationA spinal disc herniation , informally and misleadingly called a "slipped disc", is a medical condition affecting the spine due to trauma, lifting injuries, or idiopathic, in which a tear in the outer, fibrous ring of an intervertebral disc allows the soft, central portion A spinal disc herniation...
- Lumbar spinal stenosis