Spondylolisthesis (pronounced spon-dee-low-lis-thee-sis) may be best understood if we break the term down into its parts. “Spondylo” comes from the Greek word meaning “vertebra,” while “listhesis” means “to slip.” Therefore, the condition literally refers to a vertebra that has slipped out of place. While spondylolisthesis may initially sound extremely serious – as if a vertebra has completely detached and is floating somewhere in your spinal canal – it is actually a fairly common condition that involves a vertebra slipping forward or backward slightly and coming to rest against the vertebra beneath it. Many people with spondylolisthesis never even experience symptoms from the condition, and they can continue leading active lives without making any adjustments.
One thing to keep in mind when dealing with spondylolisthesis, however, is that when it does produce symptoms, they can appear in regions of the body that are not near the spine, often making it a difficult condition to diagnose. For example, discomfort in one leg may simply be the result of a muscle strain, or it could mean that a slipped vertebra is exerting pressure on your sciatic nerve. Because there is no real way for you to determine this on your own, scheduling a consultation with a physician is the only way to obtain an accurate diagnosis. The doctor will likely perform a physical examination, ask about your symptoms, and order an X-ray or MRI to determine if spondylolisthesis is truly the culprit behind your discomfort.
In the event that you do receive a diagnosis of spondylolisthesis, it will undoubtedly help you to learn about the condition, what caused it, and why it is producing symptoms, if this is the case. Gathering this information will not only help dispel your anxiety about the diagnosis, but it will also prepare you to have an informed discussion with your doctor about treatment options.
The Anatomy of Spondylolisthesis
The vertebral column typically consists of 24 individual, mobile segments of bone (vertebrae) that extend from the neck to the lower back, plus 9 fixed bones that extend into the pelvic region. Any of the 24 individual vertebrae can slip forward (anteriorly) or backward (posteriorly), but forward slippage in the lumbar spine, or lower back, is by far the most common scenario.
The lumbar spine contains five vertebrae (six in rare cases) and it is usually the fourth or fifth lumbar vertebra that is most susceptible to forward slippage. In some instances, a traumatic injury called a “hangman’s fracture” can occur, where the second cervical vertebra (in the neck) breaks and is forced over the third cervical vertebra. Contrary to what this daunting name implies, however, the injury is not usually fatal. In fact, most people survive a hangman’s fracture because the fractured vertebra actually forces the spinal canal to widen, which prevents the spinal cord from being severely damaged or crushed.
The vertebrae are made up of several parts, and it will be useful to understand the structure of vertebrae as we learn how spondylolisthesis occurs:
Vertebral body – this is the anterior portion of a vertebra and the largest part of the bone. It is cylindrical in shape and aligns with the vertebral bodies above and below it to form the front portion of the spinal column.
Intervertebral discs – these are not technically part of the vertebrae, but on the top and bottom of each vertebral body is an intervertebral disc, a tough but spongy wedge of cartilaginous tissue that absorbs shock and plays a ligamentous role in connecting all of the vertebrae.
Neural arch – also called the vertebral arch, this is the posterior (back) part of the vertebra. It resembles two bony arms branching out from the vertebral body and forming the borders around the foramina, or open canals through which spinal nerve roots pass.
Pedicles – these are the bony “arms” of the neural arch. One protrudes from each side of the vertebral body; they ultimately separate the vertebral body from the vertebral processes.
Laminae – two thin, bony plates that, with the pedicles, complete the structure of the vertebral arch. They are found on the posterior portion of the arch, behind the inferior and superior processes.
Processes – seven bony projections located around the vertebral arch, three of which allow muscles and ligaments to attach to the front and back of the spine. The other four are two pairs of superior and inferior processes found on the left and the right sides of the vertebral arch; these comprise the facet joints, which are the junctures at which adjacent vertebrae meet and articulate.
Pars interarticularis – an extremely small piece of bone between the inferior process and the superior process of each vertebra, just above the facet joints; referred to as the “pars” for short, fractures to this bone can lead to spondylolisthesis.
Now that we understand the function that each component of the vertebra plays, it will be easier to understand how spondylolisthesis occurs and how it can disrupt the structural integrity of the spine. According to the Wiltse Classification System, there are six general categories of spondylolisthesis, each defined by the underlying problem that caused the vertebral slip. They include:
Isthmic – a fracture develops on the pars interarticularis and causes the vertebra to slip forward
Degenerative –arthritic facet joints and degenerated intervertebral discs cause misalignment
Congenital – also called dysplastic, this type occurs due to a birth defect at the L5-S1 vertebrae
Traumatic – a sudden injury causing a fracture in the pars or the arch of a vertebra
Pathologic – diseases that affect the bones and cause instability, such as Paget’s disease
Iatrogenic – the result of a spine surgery that removes large portions of the anatomy
Of all these categories, isthmic spondylolisthesis and degenerative spondylolisthesis are by far the most common and it will be useful to learn more about what differentiates them.
Isthmic spondylolisthesis
· Most often occurs between the fifth lumbar vertebra (L5) and the first sacral bone (S1).
· Younger individuals between the ages five and seven are more prone to isthmic spondylolisthesis, and highly active adolescents are also susceptible.
· A pars fracture can cause the area where the bones of the facet joint meet to become unstable. The vertebral body can then slip forward and protrude over the vertebral bodies above and below it. Isthmic fractures do not always lead to spondylolisthesis, however, and bone breakage without slippage is called spondylolysis.
Degenerative spondylolisthesis
· Most often occurs between the third and fourth lumbar vertebrae (L3-L4) and the fourth and fifth lumbar vertebrae (L4-L5).
· Individuals over the age of 50 are most susceptible to degenerative spondylolisthesis, and women are three times more likely to develop the condition than men.
· It is a result of osteoarthritis in the facet joints and the gradual degeneration of the intervertebral discs, both of which cause vertebral instability.
While both isthmic and degenerative spondylolisthesis are forms of vertebral slippage, albeit with different underlying causes, it’s uncommon for isthmic spondylolisthesis to turn into degenerative spondylolisthesis. For instance, once an isthmic fracture is sustained early in life, it will likely not continue progressing over the years. In fact, a study that began in the mid 1950s when 30 children with vertebral lesions were followed over the course of 45 years showed that very few of them experienced symptoms or effects of the injury later in life. It’s far more common for degenerative spondylolisthesis to develop due to spinal osteoarthritis and degenerative disc disease than from a previous fracture.
Causes and Risk Factors of Spondylolisthesis
While the cause of isthmic spondylolisthesis is fairly black and white – a stress fracture sustained from high levels of activity causes a vertebra to slip out of place – the underlying causes of degenerative spondylolisthesis are not so clear cut. So many factors can combine to cause spinal deterioration, that it can be difficult to determine why certain people are so much more susceptible to degenerative spondylolisthesis than others. What we do know, however, is that any of the following factors can play a role in the development of osteoarthritis and degenerative disc disease, which can eventually lead to vertebral slippage:
Obesity
Smoking
Past traumatic injuries
A genetic predisposition
Prolonged periods of poor posture
High-impact exercise or contact sports
Any of these factors may eventually cause the components of the spine to degenerate, especially the facet joints and intervertebral discs. Furthermore, the simple act of getting older is a factor; for instance, the cartilage that provides a soft covering for the facet joints and that helps to stabilize them gradually wears away over many years. The surfaces of the facet joints, without their cartilage coating, may begin to grind against one another and the body often responds by growing extra deposits of bones, called bones spurs. Bone spurs don’t help the problem of degenerating cartilage, however; as a matter of fact, they can cause further instability.
Intervertebral discs, which are the spongy pads between adjacent vertebrae that absorb shock, can also weaken over time as they lose water content, collagen, and height. When enough disc height is lost, it’s possible that the vertebra above or below the degenerated disc can slip forward. This is especially common at the lumbosacral junction (L5-S1). Other components of the back that can degenerate and compromise the structural integrity of the spine include:
Ligaments – Over time, these fibrous bands of tissue that help connect and align adjacent vertebrae can harden and become enlarged.
Muscles – Older individuals may have a tendency to become sedentary, which can cause the spinal muscles to weaken.
Bones – The vertebrae can lose vitamin D, calcium, and other minerals over time, making them porous, brittle, and prone to fractures.
Ironically, degenerative spondylolisthesis is both the hardest and easiest form of the condition to prevent. On the one hand, it occurs gradually over time, so there is an opportunity to improve the overall health of your spine and reduce your risk of developing structural instability and vertebral slippage. On the other hand, there’s no way to stop the aging process; furthermore, degenerative spondylolisthesis tends not to produce any symptoms until the slippage is severe enough that it interferes with spinal nerves or the spinal cord itself, at which point preventative measures are useless.
Therefore, the best way to reduce your risk of developing any type of degenerative spine condition is to begin taking care of your back and neck as early in life as possible. Be sure to practice proper posture when sitting, standing, and lying down. Make gentle stretching and low-impact exercise regular parts of your daily routine. Try to maintain a healthy body weight and keep your bones strong with plenty of calcium and vitamin D. Most importantly, avoid smoking at all costs. The chemicals that cigarettes introduce into your body negatively affect circulation and prevent your bones, muscles, ligaments, and intervertebral discs from getting the proper nutrients.
Spondylolisthesis – Symptoms
Many people automatically associate any displacement of the vertebrae with a serious spine injury, such as hangman’s fracture, whereas lumbar (lower back) spondylolisthesis is actually a fairly common condition that can occur in varying degrees. While some people may have vertebral slippage that is so slight they’ll never experience symptoms or know they have the condition, others will find that severe vertebral slippage causes pain, affects their gait, and limits the range of motion in their lower extremities. The condition will affect everyone differently, and will depend largely on what the underlying cause of the spondylolisthesis is. For instance, someone whose vertebra was suddenly displaced in a car accident will likely experience a very different set of symptoms than someone whose vertebra has moved forward gradually over a period of 10, 20, or 30 years.
The presence and severity of symptoms may also depend on how far forward the vertebra has slipped, and if the bone has come into contact with any of the surrounding nerves, the spinal cord, or other anatomical structures. The Meyerding Grading System is the most commonly used scale to measure the severity of vertebral slippage in spondylolisthesis:
Grade I – 1% to 25%
Grade II – 26% to 50%
Grade III – 51% to 75%
Grade IV – 76% to 100%
Grade V – referred to as spondyloptosis; the L5 slips completely over the S1
Grades I and II are classified as low-grade slippage and the displaced vertebra is still considered stable. Spondylolisthesis of Grade III and above is considered high-grade and the vertebra is deemed unstable. About 90 percent of individuals with the condition have low-grade spondylolisthesis, and the majority of those cases remain asymptomatic. However, it is still possible for low-grade vertebral slippage to cause spinal nerve compression and chronic pain.
We’ve now seen that the symptoms of spondylolisthesis can vary based on the degree of vertebral slippage and the underlying cause of the slippage, but the location of the displaced vertebra within the spine also plays a large role. Since spondylolisthesis is most common in the lower back, symptoms tend to stay concentrated in the lower back and lower extremities. Symptoms can generally be divided into two categories: those caused by structural changes in the spine and those caused by nerve compression.
Symptoms of the displaced vertebra itself may include:
Pain in the lower back during physical activities that cause the spine to hyperextend
Acute pain during high-impact exercises like jogging or jumping rope (more common with isthmic spondylolisthesis)
Chronic aching sensations in the lower back (more common with degenerative spondylolisthesis)
An exaggerated curvature of the lower back, either lordosis (swayback) or kyphosis (round back)
Tight hamstring muscles when walking or running, which may produce a change in gait due to a shortened stride
Reduced flexibility and range of motion in one or both legs
Muscle spasms if the muscle fibers are overstretched to compensate for the displaced vertebra
A feeling of instability in the lower back
Pain that goes away when you sit down
Acute bouts of sharp pain
These symptoms may be compounded by radiculopathic symptoms if the slipped vertebra comes into contact with a nearby spinal nerve root, like the sciatic nerve, which is the longest nerve in the body and delivers sensation to the skin of the legs and the muscles in the back of the thighs, feet, and toes. Radiculopathic symptoms occur when a nerve root is compressed by some anatomical abnormality like a slipped vertebra, and these symptoms tend to travel and follow the entire path of the nerve. Examples of radiculopathic symptoms commonly associated with spondylolisthesis include:
Pain in the lower back
Weakness or tingling in your hips and/or buttocks
A pins-and-needles sensation that travels the length of the leg
Numbness in the legs, feet, or toes
Claudication (cramping) in the thighs and lower legs
Bowel and bladder dysfunction in extremely severe cases (this is considered a medical emergency and should be treated immediately)
Traveling symptoms are just one reason why spondylolisthesis can often be hard to diagnose. Because pain or tingling may only appear in one leg or on one side of your hip joint, it’s possible to misdiagnose the condition without a thorough physical exam, an X-ray, or an MRI. The symptoms of spondylolisthesis can also mimic other conditions, including muscle strains or ligament sprains in the lumbosacral region, herniated discs, bulging discs, arthritis, peripheral neuropathy, osteoporosis, or osteosarcoma.
This is why it’s especially important that you do not try to diagnose yourself if you’re experiencing back pain. Allow a doctor to conduct specialized tests to detect issues like gait problems, limited spinal mobility, lordosis, kyphosis, or limited flexion (ability to bend forward) or extension (ability to arch backward) in the spine.
Spondylolisthesis – Procedures
You may have already attempted a number of conservative, nonsurgical treatments that your doctor suggested to help you find relief from nerve compression caused by spondylolisthesis. But if you’ve failed to find relief through any of these treatments after several weeks or months, surgery may become an option.
At AOMSI diagnostics, we provide the most accurate spinal imaging available in the healthcare marketplace. This imaging has been proven in peer-reviewed medical journals to be the most accurate, reliable and specific spinal imaging when compared to traditional spinal imaging modalities.
Contact us today to see if AOMSI diagnostics is right for you!