The lumbar segment of the spinal column is located between the thoracic and sacral regions. It is comprised of 5 massive vertebrae interconnected with special joints and ligaments. They form a rigid system responsible for keeping our bodies upright and for supporting the weight of our upper body.
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The goal of this article is to teach you some of the most important anatomical and clinical aspects of the lumbar vertebrae. To do that, we will first look at the gross anatomy of the individual vertebrae. After that, we will dive deeper into the way the lumbar spine connects and moves, as well as the issues that can arise from various medical conditions. So, let’s jump straight into this!
Anatomy of the Lumbar Vertebra
Typical for every vertebra, the lumbar ones share similar characteristics to the rest of the vertebrae in the spine. The five lumbar vertebrae are numbered from 1 to 5 with the letter “L” before the respective number (ex. L1, L2, etc). They connect the upper portion of the spine with the sacral region of the spine which ends with the tailbone (coccyx).
Anatomically speaking, there are general and unique structures associated with the lumber segment. Let’s start with the ones that are shared across all of the spine’s vertebrae.
General characteristics and structures
The general structures found in the lumber vertebra are the:
- Body (corpus vertebrae) – It is responsible for the supportive function of the lumbar spine. In fact, the bodies of the lumber vertebrae are the largest in the spine. That’s reflective of their leading role in carrying most of the torso’s weight.
- Arches (arcus vertebrae) – They consist of two pedicles and a pair of laminae. The arches connect to the body of the vertebra via the two pedicles (pediculi arcus vertebrae). On their top and bottom surfaces, there are notches (incisura vertebralis superior et inferior). All these structures surround the vertebral foramen (large opening). Apart from having the spinal cord pass through it, the vertebral foramen is also surrounded by 7 structures that arise from the arch.
The body of the vertebrae is kidney-shaped with a slightly concave anterior surface. The vertebral foramen is triangle-shaped and relatively smaller than the one in the cervical region (but bigger than the one in the thoracic vertebrae). The reason for that is that the actual spinal cord extends only to around L2 and then continues into the so-called cauda equina (horsetail) which is significantly narrower.
The transverse processes are long and narrow, located almost entirely in the frontal segment of the vertebra. They are remnants of the embryonic lumbar ribs which is why you can also see them being called “processi costales”
The spinous process is thick and large. The reason for that is because it is the attachment point for the large muscles in the lower back. It is much more horizontal than the processes of the thoracic spine, allowing this portion of the spine to bend quite a lot.
All of the spine’s vertebra have their own unique characteristics. The ones specific to the lumbar part of the spine are the following:
- Their transversal processes are much larger than the ones on the rest of the vertebra
- Their articular facets are vertically oriented
- The spinal processes are shorter compared to the rest
- There are mammillary processes located on the upper articular facets
All these are differentiating signs that you can use when tasked to identify vertebra from different parts of the spine. Now, let’s move on to the way different vertebrae connect with each other…
Joints & Ligaments
The bodies of the different lumbar vertebrae are interconnected with intervertebral discs and ligaments. The thing that allows movement between the different vertebrae are the facet joints, while the soft disc separating them allows for better cushioning when the spine flexes in all directions.
- Intervertebral discs – They have a concave surface that lies on the adjacent vertebral surface fully covering the body of the vertebra. Their diameter is slightly larger than the one of the vertebra’s body, meaning they slightly bulge outwards. On average, their thickness is around 10-12mm. They have central and peripheral parts. The central one contains the nucleus pulposus, which is a crucial component of the biomechanical part of the spine. The peripheral parts contain collagen which forms a fibrous ring that keeps the pulpous substance protected in the center.
- Longitudinal ligaments – They are two at the front and at the back of the vertebra. The main role of these ligaments is to toughen the connection between consecutive vertebrae. They also prevent too much flexion or extension of the lower spine.
- Ligamenta flavum – these short but thick and strong ligaments connect the laminae of the vertebrae from the C2 to S1 segments. It mostly consists of elastin fibers with a little bit (20%) of collagen fibers.
The different parts of the lumbar vertebra are connected via other joints and ligaments as well. The spinal processes are connected via interspinal and supraspinal ligaments, while the transversal processes are connected via the intratransversal ligaments.
The intervertebral joints are made out of the two facet joints on both sides of each vertebra as well as the intervertebral disc in the middle.
Clinical Aspects & Diagnosis
From an etiological standpoint, the reasons for pain in the lower back are numerous. Some of the main reasons are trauma, degenerative diseases, infections, and others. Here, we will take a closer look at the most common pathology in the neurosurgery field – degenerative disc disease. Apart from being a sophisticated medical issue, it is also a social one as well. The reason for that is that it is placed very high on the list of conditions that render people temporarily incapacitated.
With time, the pulpous core of the intervertebral discs loses some of its hydrophilic properties. That leads to fibrosis, allowing some of its components to “bulge” out of the fibrous disc surrounding it. That can lead to compression to the other parts of the spinal column, including, and most crucially, the nerves going through the spine at that specific level. Apart from the bulging, another problem that arises is that the pulpous core contains osteoblasts. When in contact with the peripheral parts of the vertebra’s body, these cells can cause cell proliferation. That, in turn, leads to excess bone growth around the edges of the body.
There are numerous risk factors associated with degenerative disc disease. Some of those are:
- Old age
- Sedentary lifestyle
When it comes to its location, in almost all of the cases (90-95%) the most affected level is L4-L5.
Stages & Symptoms
There are four stages of degenerative disc disease. These are:
- Stage 1 (Dysfunction stage) – In this stage, the spine loses some of its shock protection. On top of that, the vertebrae begin to lose their natural curvature. Patients begin experiencing mild back pain, as well as pain in the neck and general discomfort.
- Stage 2 (Dehydration stage) – In this stage, patients continue experiencing loss of motor functions. The back pain is now moderate. There are noticeable spinal deformities along with bone spurs and disc dehydration.
- Stage 3 (Stabilization stage) – The pain now is severe and accompanied by muscle aches and back stiffness. There is spinal stenosis and walking might prove difficult.
- Stage 4 (Collapsing stage) – This stage is characterized by severe pain and collapse of the spinal vertebrae.
Diagnosis & Treatment
Diagnosing degenerative disc disease can be done via a couple of exams. The most commonly used ones are X-ray scans, CT scans, or MRIs. X-ray scans are cheap and reliable when it comes to finding spinal stenosis or other deformities on the vertebrae (bone spurs or fractures). Diagnosis can be difficult in the first stages of the disease but the later stages come with definitive signs that are easy to spot on routine tests.
Treatment-wise, there are usually two routes your physician can go down – conservative treatment or surgery. Choosing one or the other typically depends on the staging, the symptoms, and other factors such as age, overall condition, and more.
The conservative approach includes rest, pain management, physiotherapy, and other methods that will help with your symptoms. It is typically prescribed for around 20 days to a month. It helps in around 20% of the patients with a bulging disc.
Logically, if conservative measures bear no result, doctors will usually consider consulting a neurosurgeon. That’s done when your symptoms persist or your condition worsens.
The lumbar segment of the spine consists of 5 large vertebrae, marked as L1-L5. They are interconnected via tough joints and ligaments that serve multiple functions like cushioning the weight of the upper body as well as limiting extreme flexions. Unique structures only found in this segment of the spine are the transversal processes, the vertically oriented joints, the short spinal processes, and more. From a clinical standpoint, the most common pathology of this segment is degenerative disk disease. In various cases, it can lead to surgical intervention with good results.
This article was written and edited with the help of the National Student Neurosurgery Club “Prof. Philip Philipov”