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.
- 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|
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|
- Muscles affecting lumbar vertebrae function
- Clinical notes
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.
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.
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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 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).
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).
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 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.
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.
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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.
This refers to a spinal anomaly defined by the nonfusion of the first and second segments of the sacrum. Upon imaging, the lumbar spine will appear to have 6 vertebrae or segments instead of 5 and the sacrum will conversely appear to have only 4 segments instead of 5.
Sacralization is a congenital anomaly where the transverse process of L5 fuses to the sacrum on one or both sides, to the ilium, or to both sacrum and ilium. This anomaly usually presents bilaterally. While sacralization can cause lower back pain, it is often asymptomatic, especially in bilateral presentations since the biomechanics will not be as destabilized as a non-bilateral presentation. Finally, the L5-S1 intervertebral disc also may be thin and narrow.
Scoliosis refers to an abnormal lateral deviation or curvature, most often in the thoracic region and common among adolescent girls. Adult scoliosis however is more often related to degeneration of the lumbar spine. It is often diagnosed in parallel with spinal stenosis, a narrowing of the vertebral canal.
The lumbar lordosis refers to a normal, anteriorly convex curvature of the lumbar spine which is acquired postnatally as an upright posture is assumed when we learn to walk. The term is also used to describe an exaggerated lumbar curvature. In common jargon, this is known as “swayback,” where the lower back will be abnormally curved instead of the upper back (as in kyphosis). Lordosis is especially common in pregnancy or obesity due to the added abdominal weight that will force the lumbar vertebrae into an abnormal curvature.
Spondylolysis and spondylolisthesis
The pedicles are sometimes used as an entryway into the vertebral body for fixation with pedicle screws, or for placement of bone cement during kyphoplasty or vertebroplasty. Vertebra L5 is the most common site of spondylolysis and spondylolisthesis.
In individuals with sacralisation of vertebra L5 or lumbarization of vertebra S1, the lumbar disorders that normally affect L5 will affect L4 or L6, respectively.
Similar to in the thoracic spine, disk herniation can also occur in the lumbar spine. Since the stress resistance of the annulus fibrosus declines with age, under great enough strain or weight loading, the tissue of the nucleus pulposus can bulge through weak spots. The herniated material can end up compressing the contents of the intervertebral foramen, which include the nerve roots and blood vessels, which can result in lower back pain. Muscles affected in this region can also be weakened when the motor part of a spinal nerve is affected.
Lumbar vertebrae: want to learn more about it?
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