Spondylolisthesis: What It Means When One Spine Bone Slips Forward

Written by Ifije Ohiorhenuan, MD, PhD — Board-Certified Spine Surgeon. Last updated 2026-06-20.

Spondylolisthesis means one spinal bone has shifted, usually slightly forward, compared with the bone below it. Many cases are stable and manageable. The finding matters most when it matches symptoms such as leg pain, nerve compression, or mechanical back pain.

In my practice, I tell patients that spondylolisthesis is an alignment finding. The key question is whether that alignment problem is actually causing your symptoms.

{/ Image suggestion: Spondylolisthesis: normal alignment vs forward slip. Caption: “Spondylolisthesis means one vertebra has shifted compared with the one below it. The finding matters most when the slip narrows nerve spaces, causes abnormal motion, or matches the patient’s symptoms.” /}

What Is Spondylolisthesis?

Spondylolisthesis means one vertebra, or spine bone, has shifted compared with the vertebra below it.

Think of the spine as a stack of blocks. In spondylolisthesis, one block is not lined up perfectly with the block underneath it. That can be mild and stable. It can also be part of a more important pattern, such as nerve compression or abnormal motion.

Spondylolisthesis is most often discussed in the lumbar spine, which means the low back.

There are a few related words you may see on an X-ray or MRI report:

Anterolisthesis means a forward slip.
Retrolisthesis means a backward slip.
Lateral listhesis means a side-to-side shift. This can happen with scoliosis, which is a sideways curve of the spine, or with uneven arthritis and disc wear. You may see this in conditions like adult degenerative scoliosis.

The word “spondylolisthesis” describes alignment. It does not automatically prove the cause of your pain.

Why Spondylolisthesis Happens

There are different types of spondylolisthesis. The cause matters because it can affect symptoms, imaging, and treatment choices.

Degenerative Spondylolisthesis

Degenerative spondylolisthesis means the slip is related to wear-and-tear change in the spine.

This often involves:

Disc degeneration, which means wear or collapse of the cushion between two spine bones
Facet joint arthritis, which means arthritis in the small joints in the back of the spine
Thickened ligaments, which are bands of tissue that support the spine
Narrowing around the nerves

Degenerative spondylolisthesis often occurs at L4-L5, one of the lower levels of the lumbar spine. It can occur at other levels too.

It is commonly seen with lumbar spinal stenosis. Lumbar spinal stenosis means narrowing of the spinal canal in the low back. The spinal canal is the main tunnel where nerves travel.

Disc collapse and arthritis can also overlap with lumbar degenerative disc disease.

Isthmic Spondylolisthesis and Pars Defects

Isthmic spondylolisthesis usually involves a problem in a small bridge of bone called the pars interarticularis. The pars is part of the back of the vertebra.

A defect or stress fracture in this area is called spondylolysis, also called a pars fracture. When a pars defect allows the vertebra to slip, that slip is called spondylolisthesis.

Isthmic spondylolisthesis is often seen at L5-S1. It may begin earlier in life, sometimes during the teenage years. It may not cause major symptoms until later.

Learn more about spondylolysis, also called a pars fracture.

Other Less Common Causes

Less common causes include:

Congenital or developmental differences, which means spine alignment differences present from birth or growth
Trauma, such as a fracture from an injury
Prior spine surgery
Pathologic causes, which means a serious disease process such as tumor or infection

Tumor and infection are uncommon causes, but they are important when symptoms or imaging raise concern.

What Does L5-S1 Spondylolisthesis Mean?

L5-S1 is the lowest mobile level of the lumbar spine. It is where the L5 vertebra meets the sacrum, which is the triangular bone at the back of the pelvis.

L5-S1 spondylolisthesis means the L5 vertebra has shifted compared with the sacrum.

At L5-S1, the slip is often related to a pars defect. But it can also be related to arthritis, disc degeneration, or other changes.

Symptoms can include:

Low back pain
Buttock pain
Pain down the leg
Numbness or tingling
Symptoms that feel worse with standing, walking, or bending backward in some people

When I see L5-S1 spondylolisthesis, I pay close attention to the L5 nerve roots and the foramina.

A nerve root is a branch of nerve that leaves the spine and travels into the leg. A foramen is the side opening where that nerve exits. If the slip narrows the foramen, it can irritate or compress the L5 nerve root.

That can cause leg pain that feels like sciatica. Sciatica means pain that travels from the low back or buttock down the leg because a nerve is irritated.

What Do the Grades of Spondylolisthesis Mean?

Spondylolisthesis is often described by grade. The grade estimates how far one vertebra has slipped compared with the bone below it.

Low-Grade vs High-Grade Slips

A common system is called the Meyerding grading system.

Typical grades are:

Grade	Amount of slip
Grade 1	0–25%
Grade 2	25–50%
Grade 3	50–75%
Grade 4	75–100%
Grade 5	Complete slip, also called spondyloptosis

Spondyloptosis means the upper vertebra has slipped completely off the bone below it. This is uncommon.

Most adult cases are low-grade, meaning Grade 1 or Grade 2.

The grade is useful, but it is not the whole story. In practice, I care about whether the slip is stable, whether nerves are compressed, and whether the symptoms fit the imaging.

A low-grade slip can be very painful in one person and an incidental finding in another. An incidental finding means something seen on imaging that may not be the main cause of symptoms.

Learn more about spondylolisthesis grading.

Symptoms: What Spondylolisthesis Can Feel Like

Spondylolisthesis can cause symptoms in different ways. It can also be present on imaging without being the main pain source.

Back Pain

Back pain from spondylolisthesis can be mechanical. Mechanical back pain means pain linked to movement, posture, load, or abnormal stress on the spine.

It may feel worse with:

Standing
Bending backward
Lifting
Twisting
Long periods of activity

It may feel better with sitting or bending forward, especially if spinal stenosis is also present.

But back pain is very common. A slip on an MRI or X-ray does not always prove that the slip is the cause.

Leg Pain, Numbness, or Tingling

Spondylolisthesis can cause leg symptoms when it narrows nerve spaces.

This may happen through:

Foraminal stenosis, which means narrowing of the side tunnel where a nerve exits the spine
Central stenosis, which means narrowing of the main spinal canal
Lateral recess stenosis, which means narrowing of a smaller nerve pathway inside the canal

When a nerve is squeezed or irritated, pain can travel down the leg. This may feel like burning, shooting, electric pain, numbness, or tingling.

This pattern is often called sciatica.

Walking or Standing Intolerance

When spondylolisthesis occurs with stenosis, some people get leg symptoms with standing or walking.

This is called neurogenic claudication. Neurogenic means nerve-related. Claudication means pain, heaviness, or weakness that comes on with walking or standing.

Symptoms may improve with:

Sitting
Leaning forward
Bending over a shopping cart
Taking breaks while walking

This pattern is common in lumbar spinal stenosis.

How Doctors Diagnose Spondylolisthesis

Diagnosis is not based on one word in a report. It comes from matching your symptoms, exam, and imaging.

X-rays

X-rays show bone alignment.

Standing X-rays often show alignment better than a lying-down MRI because your spine is under body weight.

In selected cases, doctors may use flexion-extension X-rays. These are X-rays taken while bending forward and backward. They can help show whether the slipped level moves more than expected.

This is one way doctors assess instability, which means abnormal motion at a spine level.

Not every person with spondylolisthesis needs bending X-rays.

MRI

MRI stands for magnetic resonance imaging. It uses magnets to make detailed pictures of the spine.

MRI can show:

Nerves
Discs
Stenosis
Soft tissues
Nerve compression
Inflammation around some structures

MRI may show the slip, but it is especially useful for seeing whether nerves are compressed.

Because MRI is usually done lying down, the slip may look smaller than it does on standing X-rays in some people.

CT Scan

CT stands for computed tomography. It uses X-rays and computer processing to show bone detail.

A CT scan can help show:

Pars defects
Fractures
Bone anatomy
Prior fusion anatomy
Details needed for surgical planning

CT is not always necessary.

Matching Imaging to Symptoms

This is the most important step.

Many spine findings become more common with age. Some findings matter. Some do not. The key is whether the finding matches the pattern of pain, numbness, weakness, walking limits, and exam findings.

What I look for on MRI is not just the word “spondylolisthesis.” I look for whether the slip is narrowing the spinal canal or the nerve exit tunnels.

After Diagnosis: How to Understand Whether Your Spondylolisthesis Matters

If your MRI report says spondylolisthesis, anterolisthesis, pars defect, foraminal stenosis, or nerve compression, the most important question is not just “What does the word mean?” It is “Does this finding actually explain my symptoms, and what category of next step makes sense?”

Want a spine surgeon to translate your MRI report?
SpineClarity offers a written MRI/case review from a board-certified spine surgeon. You can upload your symptoms, MRI report, and relevant records and receive a plain-language written interpretation with a suggested next-step category. This is not emergency care and does not replace an in-person physician relationship, but it can help you understand what your report is saying and what questions to ask next.

Treatment Options for Spondylolisthesis

Treatment depends on the cause of the slip, the symptoms, the nerves, and whether the spine is stable.

In my practice, surgery is not based on the MRI report alone. It is based on the pattern of symptoms, the neurologic exam, the degree of nerve compression, and whether the spine is stable.

Observation and Activity Modification

Some mild, stable slips do not require invasive treatment.

Observation means watching the condition over time while paying attention to symptoms and function.

Activity modification means adjusting painful activities. This may include changing lifting habits, limiting repeated extension, pacing walking, or changing exercise choices.

This does not mean ignoring progressive weakness, worsening leg symptoms, or red flags.

Physical Therapy

Physical therapy may focus on:

Core strength
Hip mobility
Posture
Walking and conditioning
Balance
Symptom-guided activity
Safer lifting and movement patterns

Physical therapy usually does not “put the bone back.” The goal is to improve strength, mechanics, and symptom control.

Medications

Medications may be used in some cases to reduce pain enough to move and function better.

Options sometimes include:

Anti-inflammatory medicines
Acetaminophen
Nerve pain medications

Medication decisions depend on your medical history and treating clinician. This is especially important if you have kidney disease, stomach ulcers, bleeding risk, heart disease, liver disease, medication allergies, or take blood thinners.

Injections

Injections may be considered when pain appears to come from a specific inflamed structure.

An epidural steroid injection places anti-inflammatory medicine near irritated spinal nerves. It may help selected people with nerve-related leg pain.

Other injections may target facet joints or pars-related pain pathways in selected cases.

Injections may reduce inflammation or pain. They do not correct the slip.

Surgery

Surgery may be considered when symptoms are severe, persistent, neurologic, or linked to clear nerve compression or instability after appropriate evaluation.

Common surgical ideas include:

Decompression, which means creating more room for nerves
Fusion, which means stabilizing a painful or unstable spine level so the bones heal together
Interbody fusion, which means placing a spacer in the disc space between two vertebrae as part of a fusion plan

Not every spondylolisthesis surgery is the same.

Some people may be considered for decompression alone. Others may need decompression with fusion. The choice depends on the anatomy, stability, slip type, stenosis pattern, foraminal narrowing, and surgeon judgment.

If a fusion is discussed, you may hear terms like TLIF or PLIF. Learn more about TLIF vs PLIF.

When Spondylolisthesis Is More Urgent

Most spondylolisthesis findings are not emergencies, but certain neurologic symptoms should not wait for an online review.

Seek urgent medical care now, or call emergency services, if you have:

New loss of bladder control
New loss of bowel control
Numbness in the groin, inner thighs, or saddle area
Rapidly worsening leg weakness
Severe new weakness, such as a new foot drop
Difficulty walking because of new or worsening neurologic weakness
Fever with severe back pain, especially if infection is possible
Unexplained weight loss with severe back pain
History of cancer with new severe or progressive spine pain
Recent major trauma with new severe back pain
Severe back pain with concern for infection, tumor, fracture, or cauda equina syndrome

Cauda equina syndrome is a rare but serious condition where the nerves at the bottom of the spinal canal are compressed. It can affect bladder, bowel, sexual function, and leg strength.

Learn more about cauda equina syndrome.

An online MRI or case review is not emergency care. If you have new bladder or bowel problems, saddle numbness, rapidly worsening weakness, or severe new neurologic symptoms, seek urgent medical evaluation.

What I Look For When Reviewing a Spondylolisthesis MRI

When I review a spondylolisthesis MRI, I look for the full pattern.

I look at:

The level of the slip, such as L4-L5 or L5-S1
The direction of the slip: forward, backward, or sideways
The degree of slip
Whether there is central stenosis
Whether there is foraminal stenosis
Which nerve roots may be affected
Whether there is a pars defect
Whether there is disc collapse
Whether there is facet joint arthritis
Whether the MRI was done lying down
Whether standing X-rays may show a different alignment
Whether your symptoms match the imaging

The MRI report may list several findings. The real value is in sorting them into a clear picture.

For example, “Grade 1 anterolisthesis” may sound frightening. But the key questions are:

Is it stable?
Is a nerve compressed?
Does the nerve match the pain pattern?
Is there stenosis?
Is there a pars defect?
Are symptoms mainly back pain, leg pain, or walking intolerance?
Are there signs of neurologic weakness?

That context helps decide whether the next step is reassurance, therapy, injections, more imaging, surgical evaluation, or urgent care.

FAQ

Is spondylolisthesis serious?

Sometimes. Many cases are mild or stable. Seriousness depends on symptoms, nerve compression, neurologic findings, and whether the slip is progressing.

A mild slip on imaging does not automatically mean your spine is dangerous.

Can spondylolisthesis cause sciatica?

Yes. Spondylolisthesis can cause sciatica if it narrows the space where a nerve exits the spine or contributes to stenosis.

This can irritate or compress a nerve and cause pain down the leg.

What does L5-S1 spondylolisthesis mean?

It means the L5 vertebra has shifted compared with the sacrum.

The significance depends on the amount of slip, whether the L5 nerve root is compressed, whether the foramen is narrowed, and whether the symptoms match the imaging.

Does spondylolisthesis always need surgery?

No. Many cases are treated without surgery.

Surgery is considered when symptoms, nerve compression, instability, or neurologic problems justify it.

Can physical therapy fix spondylolisthesis?

Physical therapy generally does not move the bone back into place.

It can improve strength, mechanics, posture, conditioning, and symptom control.

Can spondylolisthesis get worse?

It can, but many adult low-grade slips remain stable.

Progression risk depends on the cause, age, anatomy, and spine mechanics.

What is the difference between spondylolysis and spondylolisthesis?

Spondylolysis is a pars defect or stress fracture.

Spondylolisthesis is the slip. A pars defect can lead to a slip.

What is the difference between anterolisthesis and spondylolisthesis?

Anterolisthesis is a forward slip.

It is one type of spondylolisthesis.

What grade of spondylolisthesis needs surgery?

Grade alone does not determine surgery.

Symptoms, nerve compression, instability, neurologic findings, and disability matter more than the grade by itself.

Can my MRI show spondylolisthesis accurately?

MRI can show the slip and nerve compression.

But MRI is usually done lying down. Standing X-rays may better show alignment under body weight in selected cases.

References

Brinjikji, W., Luetmer, P. H., Comstock, B., et al. (2015). Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR American Journal of Neuroradiology, 36(4), 811–816. https://doi.org/10.3174/ajnr.A4173

Chaput, C., Padon, D., Rush, J., Lenehan, E., & Rahm, M. (2007). The significance of increased fluid signal on magnetic resonance imaging in lumbar facets in relationship to degenerative spondylolisthesis. Spine, 32(17), 1883–1887.

Chou, R., Hashimoto, R., Friedly, J., et al. (2015). Epidural corticosteroid injections for radiculopathy and spinal stenosis: A systematic review and meta-analysis. Annals of Internal Medicine, 163(5), 373–381. https://doi.org/10.7326/M15-0934

Fredrickson, B. E., Baker, D., McHolick, W. J., Yuan, H. A., & Lubicky, J. P. (1984). The natural history of spondylolysis and spondylolisthesis. Journal of Bone and Joint Surgery. American Volume, 66(5), 699–707.

Gardner, A., Gardner, E., & Morley, T. (2011). Cauda equina syndrome: A review of the current clinical and medico-legal position. European Spine Journal, 20(5), 690–697. https://doi.org/10.1007/s00586-010-1668-3

Ghogawala, Z., Dziura, J., Butler, W. E., et al. (2016). Laminectomy plus fusion versus laminectomy alone for lumbar spondylolisthesis. New England Journal of Medicine, 374(15), 1424–1434. https://doi.org/10.1056/NEJMoa1508788

Kalichman, L., & Hunter, D. J. (2008). Diagnosis and conservative management of degenerative lumbar spondylolisthesis. European Spine Journal, 17(3), 327–335. https://doi.org/10.1007/s00586-007-0543-3

Kalichman, L., Kim, D. H., Li, L., Guermazi, A., Berkin, V., & Hunter, D. J. (2009). Spondylolysis and spondylolisthesis: Prevalence and association with low back pain in the adult community-based population. Spine, 34(2), 199–205. https://doi.org/10.1097/BRS.0b013e31818edcfd

Koslosky, E., & Gendelberg, D. (2020). Classification in Brief: The Meyerding Classification System of Spondylolisthesis. Clinical Orthopaedics and Related Research, 478(5), 1125–1130. https://doi.org/10.1097/CORR.0000000000001153

North American Spine Society. (2014). Evidence-Based Clinical Guidelines for Multidisciplinary Spine Care: Diagnosis and Treatment of Degenerative Lumbar Spondylolisthesis. North American Spine Society.

Patel, N. D., Broderick, D. F., Burns, J., et al. ACR Appropriateness Criteria® Low Back Pain. Journal of the American College of Radiology. American College of Radiology.

Resnick, D. K., Watters, W. C., Mummaneni, P. V., et al. (2014). Guideline update for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 9: Lumbar fusion for stenosis with spondylolisthesis. Journal of Neurosurgery: Spine, 21(1), 54–61. https://doi.org/10.3171/2014.4.SPINE14274

Spondylolisthesis. In: StatPearls. Treasure Island, FL: StatPearls Publishing. NCBI Bookshelf.

Austevoll, I. M., Hermansen, E., Fagerland, M. W., et al. (2021). Decompression with or without fusion in degenerative lumbar spondylolisthesis. New England Journal of Medicine, 385(6), 526–538. https://doi.org/10.1056/NEJMoa2100990

Weinstein, J. N., Lurie, J. D., Tosteson, T. D., et al. (2007). Surgical versus nonsurgical treatment for lumbar degenerative spondylolisthesis. New England Journal of Medicine, 356(22), 2257–2270. https://doi.org/10.1056/NEJMoa070302