What is Isthmic Spondylolisthesis?
Normally, the lower spine (lumbar spine) maintains a particular alignment, where each bone in the spine (vertebral body) lines up directly with the one above and below it. In simpler terms, the lower front part of the upper bone should match with the upper part of the lower bone. Sometimes, a condition occurs called spondylolisthesis, in which one bone in the lower spine moves forward compared to its neighboring bone. Usually, this creates ongoing symptoms. Commonly, the main symptom is back pain, sometimes along with leg pain. However, if spondylolisthesis happens suddenly due to an accident or cancerous tumors, it can lead to nerve-related symptoms including loss of control over bowel or bladder function.
The severity of spondylolisthesis is classified using a system called the Meyerding Classification. It measures how far the upper bone has moved forward compared to the lower bone in terms of percentage. Accordingly, Grade 1 represents less than 25% bone movement, Grade 2 is 25% to 50% movement, Grade 3 is 50% to 75%, Grade 4 is 75% to 100%, and Spondyloptosis is when the upper bone has moved forward more than 100%.
Spondylolisthesis can be caused by a variety of factors such as birth defects, natural wear and tear, injury, disease, or surgical manipulation. A type of spondylolisthesis called isthmic spondylolisthesis relates to a defect in a specific part of the bone called the pars interarticularis, which results in forward bone movement over time. It usually impacts the bones at the base of the spine. This shift can trigger back pain and narrow the spinal canal or openings between the bones through which nerves pass, potentially leading to nerve compression.
What Causes Isthmic Spondylolisthesis?
Isthmic spondylolisthesis is often caused by instability in an area of the back called the pars interarticularis, which could affect one side or both. The pars interarticularis is the part of the spine that connects important structures of the vertebrae, or individual bones in the spine. This includes the lamina, pedicle, and transverse processes. It also connects the facet joints, which are small, stabilizing joints between and behind adjacent vertebrae.
If there’s a defect in this connecting structure, it’s essentially like cutting the cord that keeps the vertebrae aligned properly. This allows the upper vertebra to slide forward over the one below it, a condition known as spondylolisthesis.
Research shows that the part of the spine that endures the most physical stress is the pars interarticularis. This makes it prone to stress fractures, which can repeatedly heal and fracture over time, leading to chronic fractures or an elongated pars without a noticeable defect—suggesting a history of recurring fracture healing.
These fractures in the pars interarticularis are often due to repeated movements. So, activities that involve a lot of bending and straightening, putting pressure on the spine, or rotational motions carry a greater risk. People who play golf, lift weights, or participate in activities like baseball, football, and gymnastics could be more prone to these pars defects.
Risk Factors and Frequency for Isthmic Spondylolisthesis
Isthmic spondylolisthesis is a condition that affects about 4% to 8% of people. It is more common in males, with males being three times more likely to have it than females. A study involving 3,529 patients from the Framingham Heart Study has found an interesting fact. It notes that 20% of patients with a specific defect, identified through a CT scan, showed no signs of spondylolisthesis. Furthermore, the study found that the risk of developing spondylolisthesis increases significantly from the fifth to the eighth decade of a person’s life.
- Isthmic spondylolisthesis affects 4% to 8% of the general population.
- It’s three times more common in males compared to females.
- A study involving 3,529 patients found that 20% with a certain kind of defect in their spine did not show signs of spondylolisthesis.
- This study also revealed that the risk of spondylolisthesis rises dramatically from one’s 50s to 80s.
Signs and Symptoms of Isthmic Spondylolisthesis
Isthmic spondylolisthesis is a condition which often doesn’t show any symptoms. However, when symptoms do occur, the most common one is low back pain, which can vary from person to person. Some people may also have back and leg pain that gets worse with walking. It’s important to note that this should not be confused with pain related to blood flow issues, which gets better when you rest.
Other symptoms depend on which nerve is being pressed upon by the misaligned bone and how severe the misalignment or narrowness of the spinal canal is. Physical examination may reveal a range of conditions – from no noticeable issues to severe issues like loss of ability to move.
The most commonly observed signs are lack of normal deep tendon reflexes, signs of pain when the leg is straightened, and reduced sensation. Some patients might have weakness in the lower body, specifically tied to pain.
Rarely, patients with ongoing isthmic spondylolisthesis do not show significant weakness in movement. But sudden occurrence of isthmic spondylolisthesis can lead to complete paralysis and loss of bowel and bladder function.
As the L5-S1 area is most commonly affected by this condition, symptoms related to the L5 nerve – such as weakness in lifting the foot and the big toe – are often observed.
- Low back pain
- Back and leg pain that gets worse with walking
- Signs of pain when the leg is straightened
- Lack of normal deep tendon reflexes
- Reduced sensation
- Weakness in the lower body
- Complete paralysis and loss of bowel and bladder function (in severe cases)
- Weakness in lifting the foot and the big toe
Testing for Isthmic Spondylolisthesis
If you initially come in with lower back pain, you typically wouldn’t need an imaging test because this type of pain usually subsides on its own. However, your doctor will still need to make sure serious conditions like tumors or infections are not the cause of your pain. They will do this through asking you detailed questions about your symptoms (a high-quality history) and doing a thorough physical exam.
If your back pain doesn’t improve with simple treatments, then your doctor might order plain X-rays. These imaging tests create pictures of the structures inside your body and can help your doctor see the position, quality, and stability of the bones in your lower (lumbar) spine.
If your pain also includes symptoms like tingling, numbness, or weakness that tracks along a nerve pathway (radicular symptoms) or discomfort in your legs that worsens when you walk or stand and eases when you sit or bend forward (neurogenic claudication), you may have a problem with the nerves in your spine. To check for these nerve-related issues, your doctor may order a different type of imaging test like an MRI (magnetic resonance imaging) or a CT myelogram (a specialized CT scan that involves injecting a contrast dye into the spinal canal) of your lumbar spine.
The oblique view X-ray, or an X-ray taken from an angle, is good at spotting problems in the pars interarticularis, a small, narrow part of the vertebra. A CT scan is the definitive way to confirm if this pars defect is present. An MRI is the preferred tool to look at the softer structures in your lumbar spine like the intervertebral discs (the cushions between your vertebrae), the ligamentum flavum (a ligament that helps stabilize your vertebrae), the thecal sac (the tube that contains your spinal cord), the nerve roots, and the conus medullaris (the last part of your spinal cord). If you’ve tried conservative treatments and they haven’t worked, and you’re considering surgery, an MRI would be needed.
Treatment Options for Isthmic Spondylolisthesis
If you’re experiencing low back pain due to isthmic spondylolisthesis, which is a condition where a vertebrae in the spine moves out of place, the first line of treatment usually involves non-surgical methods. This could include modifying your activities to avoid certain movements that cause pain, taking pain relievers such as non-steroidal anti-inflammatory drugs (NSAIDs) or muscle relaxants, performing physical therapy exercises, or receiving epidural steroid injections which deliver medication directly to the painful area.
If these methods don’t reduce your back pain, or if the pain is so severe that it’s significantly impacting your quality of life, then your doctor may consider referring you to a specialist for further evaluation. Imaging tests may also be required if you’re experiencing symptoms like neurogenic claudication or radiculopathy, which are characterized by pain, numbness, or weakness radiating down the leg.
If non-surgical methods are unsuccessful, surgical options might be considered. These could involve decompression surgery, which is aimed at relieving pressure on the nerves, or a more complex procedure that combines decompression with internal fixation, a technique that stabilizes the spine using hardware such as screws or rods. This procedure also involves a bony fusion to prevent the vertebrae from slipping out of place again in the future.
In cases where isthmic spondylolisthesis causes acute symptoms due to traumatic injury or cancer, urgent surgical intervention may be required.
What else can Isthmic Spondylolisthesis be?
When a doctor is trying to diagnose a health issue related to spondylolisthesis, which is a condition where a bone in the spine slips out of place, they might consider these possibilities:
- Degenerative spondylolisthesis: caused by wear and tear or aging
- Traumatic spondylolisthesis: caused by an injury or trauma
- Dysplastic spondylolisthesis: a congenial type, present from birth
- Pathologic spondylolisthesis: caused by diseases like a tumor, infection, or due to a medical procedure gone wrong
