The Lumbar Vertebrae | Lumbar Vertebra
The human vertebral spine has 24 distinct movable segments, and 8-10 segments that fuse to become the sacrum and coccyx after birth. With the exception of the first two cervical vertebrae (Axis and Atlas) the general shape and elements of each vertebrae are essentially the same. In the vertebral spine, there are 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae. Below the last lumbar vertebra is the first segment of the sacrum. Each vertebra in the cervical, thoracic, and lumbar spine have a vertebral body, vertebral arch, vertebral foramen, 4 superior and inferior articular processes, two transverse processes, 2 lamina, and 2 pedicles. The differences between the sections of the lumbar vs. other vertebrae mainly include the differences in size of elements such as the vertebral bodies, which are much thicker and stronger to absorb greater pressures of gravity due to their position at the bottom of the spine. These vertebra, along with the intervertebral discs that separate them, take on a lot of force due to their position at the bottom of the torso and our center of gravity. The lumbar curve, more massive lumbar vertebral bodies and discs, and the overall curve of the spine are designed to disperse much of the pressure away from these lower back elements and into the pelvic area and lower extremities. The overall makeup is often sufficient enough to decompress the lower back structures enough so that most of us never experience lower back pain, or just transient pain symptoms when they do occur. In some cases, though, the inherent compression pressures of the forces of gravity, coupled with other factors such as obesity and muscular deconditioning, overwhelm the discs and other structures that support the lower back. These back problems may present as conditions such as lordosis, lateral scoliosis, degenerative disc disease, and lumbar herniated discs.
Let's take a look at the anatomy and physiology of the lumbar vertebrae.
Lumbar Vertebrae: The lumbar vertebrae are the last five "true" vertebrae in the spine. There are five lumbar vertebrae in this section, and are also labeled as L1-L5. The number labeling goes as follows: L1 is the vertebra at the top of the section and L5 is the vertebra at the bottom of the section. Together, these vertebra make up the Lumbar Curve. The lumbar curve is convex forward (anteriorly) and concave backward. Because of this shape/angle of curvature, the lumbar curve is also known as the Lordotic Curve. Because the Cervical Curve/Cervical Spine also have the same direction of curvature, it is also described as a lordotic curve. The Lordotic curve is normal and not to be confused with the back condition known as lordosis, which is an excessive curvature in this same direction, but at an increased angle.
The normal Lumbar Lordosis curvature is 40-60 degrees. Any degree of curvature beyond this angle may be diagnosed as lordosis.
The lumbar vertebrae are more massive and heavier than the other vertebrae, as an adaptation to their primary purpose of being weight-bearing structures.
Their somewhat kidney-shaped vertebral bodies are wider in the transverse than in the anteroposterior diameter. The lumbar vertebrae have large bean shaped bodies that increase in size from top to bottom. Their bodies are deeper in front than behind and their superior and inferior surfaces are flattened or slightly concave. The body of the 5th lumbar segment is considerably deeper in front than behind, which gives it a wedge shape that adapts for articulation with the sacrum.
Transverse processes: they are smaller than those of the thoracic region. The upper three pairs are directed almost exactly laterally, while the two lower pairs turn slightly upward.
Spinous processes: the lumbar spinous processes are large, thick and blunt and project horizontally backward.