What Is Spondylolisthesis? Grades, Causes, and Symptoms

Spondylolisthesis is a word many people first see on an X-ray or MRI report, often with a grade attached. This article explains what the slip is, how it is graded, the main causes, which symptoms it can produce, and how clinicians decide whether it needs treatment.

What “slip” means in the spine

The spine is a stack of vertebrae connected by discs at the front and small facet joints at the back. Together with ligaments and muscles, these structures keep each vertebra aligned with the one below it.

In spondylolisthesis, that alignment changes and a vertebra shifts forward relative to the one beneath it. The term comes from Greek words for vertebra and slippage. A forward slip is also called anterolisthesis. A backward slip, called retrolisthesis, is less common and usually discussed separately.

According to StatPearls, a peer-reviewed clinical reference published by the National Library of Medicine, slips can occur anywhere in the spine but are most clinically relevant in the lumbar spine and at the junction of the lumbar spine and sacrum, L5-S1.

A slip is not a sudden dislocation. In adults it usually develops gradually and may have been present for years before anyone notices it.

How spondylolisthesis is graded

The most widely used system is the Meyerding classification. As explained in a Clinical Orthopaedics and Related Research summary of the system, it is measured on a standing side-view X-ray. The forward shift of the upper vertebra is expressed as a percentage of the length of the vertebra below.

The grade describes the amount of displacement. It does not, by itself, describe symptoms, whether the level is moving abnormally, or which treatment is appropriate. Clinicians may add bending X-rays, called flexion-extension views, to see whether the slip changes with movement.

What causes spondylolisthesis

The Wiltse classification, first published by Wiltse, Newman, and Macnab in 1976, groups slips by their underlying cause into five main types:

1. Dysplastic (Type I): a congenital malformation of the lower lumbar spine that weakens its stability.
2. Isthmic (Type II): a defect or stress fracture in the pars interarticularis, a thin bridge of bone connecting the upper and lower joints at the back of the vertebra.
3. Degenerative (Type III): age-related wear in the disc and facet joints that allows gradual slippage.
4. Traumatic (Type IV): an acute fracture of the back of the vertebra outside the pars.
5. Pathologic (Type V): bone weakened by disease, such as a tumor, infection, or metabolic bone disorder.

Slips can also follow spine surgery that removes a large amount of supporting bone. This is sometimes called iatrogenic spondylolisthesis. The type describes the cause and is separate from the grade, which describes how far the vertebra has moved.

Degenerative and isthmic: the two most common adult types

Most adults with spondylolisthesis have one of two types, and they behave differently.

Degenerative spondylolisthesis develops as discs lose height and facet joints wear, reducing the structures that normally resist forward sliding. StatPearls notes that it most commonly affects the L4-L5 level and is seen particularly in older adults and postmenopausal women. In a Framingham Study CT analysis of 188 adults aged 40 to 80, degenerative spondylolisthesis was about three times more common in women than in men, and its prevalence increased from the fifth through the eighth decades of life.

Degenerative slips are closely linked to lumbar spinal stenosis. Because the pars is intact, the back of the vertebra moves forward together with the body, which can narrow the canal. Our overview, What Is Lumbar Spinal Stenosis?, explains how that narrowing causes symptoms.

Isthmic spondylolisthesis starts with a pars defect, called spondylolysis. These defects often begin in adolescence, particularly with sports involving repeated back arching such as gymnastics or football, and may not cause symptoms until adulthood. Isthmic slips most often affect L5-S1 and are more common in males. In the same Framingham CT study, the prevalence of spondylolysis was 11.5%, and about a fifth of people with defects on both sides had no measurable slip.

Symptoms, and why imaging does not tell the whole story

Many people with spondylolisthesis have no symptoms. It is often found on imaging done for another reason.

In the Framingham CT study, researchers found no significant association between spondylolysis, isthmic spondylolisthesis, or degenerative spondylolisthesis and low back pain in the preceding year. That finding does not mean slips never cause pain. It means that seeing a slip on a scan is not, on its own, proof that it explains someone’s symptoms.

When symptoms do occur, they may include:

• Low back pain, often activity-related and eased by rest.
• Neurogenic claudication: leg pain, heaviness, numbness, or weakness caused by pressure on nerves in the lower spine, typically worse with standing and walking and eased by sitting or bending forward. This usually reflects stenosis at the level of the slip.
• Radiculopathy: pain, numbness, or weakness following the path of a single nerve root, often from narrowing of the opening where that nerve exits.

Position-related back pain has many possible causes. Lower Back Pain When Standing vs. Sitting compares them.

Seek urgent care for new bladder or bowel control problems, numbness in the groin or inner thighs, or rapidly worsening leg weakness. These are uncommon but can indicate severe nerve compression.

Spondylolysis in teenagers and young athletes

Isthmic spondylolisthesis often begins long before adulthood. StatPearls explains that the most common form starts as a fatigue fracture of the pars interarticularis caused by repeated backward bending of the lower spine. It is frequently seen in young athletes in sports such as wrestling, football, and gymnastics. People whose pars bone is naturally thinner may be more prone to these stress injuries.

When symptoms occur, they usually take the form of low back pain that comes and goes, may worsen with bending forward or backward, and tends to be linked to activity. Some pars defects cause no symptoms at all. Not every defect progresses to a slip, and many stay stable.

Imaging choices differ slightly at this age. StatPearls notes that MRI is particularly sensitive for detecting early stress reactions and bone swelling before a full fracture line forms, while CT remains the best test for showing an established defect in the bone.

The outlook for many young patients is reassuring. According to StatPearls, spondylolysis and low-grade slips in children and adolescents often remain stable, and some pars defects heal on their own. Healing rates are highest when the defect is on one side only or is caught early. Treatment typically involves a break from the aggravating sport, physical therapy, and sometimes a brace, followed by a gradual return to activity guided by the treating clinician.

Parents and coaches should take persistent back pain in a young athlete seriously rather than assuming it is a muscle strain, especially when it keeps returning with the same movements.

How it is diagnosed

Diagnosis combines symptoms, examination, and imaging.

• Standing lateral X-rays show the slip and allow grading. Flexion-extension views show whether it moves.
• MRI shows the discs, ligaments, and nerves, and whether the slip is narrowing the canal or nerve openings.
• CT shows bone detail best. StatPearls describes it as the gold standard for identifying pars defects.

Clinicians also consider features beyond the grade: whether the level moves abnormally, the location and degree of stenosis, overall spinal alignment, and whether symptoms are mainly in the back or the legs.

Treatment considerations

The goals of treatment are to relieve symptoms and preserve function, not to “fix” a number on an X-ray.

Non-surgical care

Non-surgical care is usually the starting point for low-grade slips. StatPearls notes that the natural history of low-grade spondylolisthesis is typically favorable and that adults with low-grade slips rarely experience significant progression, although age-related disc changes can still cause symptoms to worsen.

StatPearls describes these non-surgical options:

• Activity modification, reducing movements that reliably provoke symptoms while staying generally active.
• Physical therapy focused on core stabilization, lumbar flexibility, and hamstring stretching, to reduce mechanical strain and improve posture.
• Anti-inflammatory medicines for symptom control.
• Bracing, used selectively for symptomatic instability, particularly in younger patients.
• Epidural steroid injections, which may give temporary relief when leg pain comes from an irritated nerve root.
• Medial branch blocks and radiofrequency ablation, which target the small nerves supplying the facet joints and may be considered for back pain associated with spondylolysis.

Progress is usually judged by function, such as walking distance, sleep, and the ability to work, rather than by changes on repeat X-rays.

Surgical options

Surgery is generally discussed for persistent, limiting nerve symptoms despite non-surgical care, progressive weakness, high-grade or worsening slips, or instability. The main approaches are:

• Decompression, which removes tissue compressing the nerves.
• Decompression with fusion, which also stabilizes the level so it no longer moves.
• Decompression with a motion-preserving implant, available for a narrowly defined group.

The North American Spine Society’s evidence-based guideline on degenerative spondylolisthesis, which reviewed studies published up to May 2013, suggests decompression with fusion to improve clinical outcomes compared with decompression alone in people with symptomatic stenosis and degenerative spondylolisthesis. It also states that for symptomatic single-level slips of less than 20%, without narrowing of the side openings where nerves exit (foraminal stenosis), decompression alone that preserves the midline structures gives equivalent outcomes. Both recommendations are graded B, meaning they rest on fair-quality evidence. Two major randomized trials published after that review, in 2016, reached different conclusions about when fusion adds benefit, which is covered in What Is Lumbar Spinal Fusion?

One motion-preserving option, the TOPS System (the link goes to the manufacturer’s website), has FDA approval for a specific indication that includes Grade I degenerative spondylolisthesis at one level from L3 to L5 with moderate to severe stenosis, in people aged 35 to 80. The FDA also lists situations where it should not be used, including slips greater than Grade I and non-degenerative types of spondylolisthesis. Our comparison of fusion and TOPS explains what each approach is designed to do, without assuming either is the right choice for a given person.

A slip seen on imaging does not by itself mean stabilization is needed. The decision depends on symptoms, the type and grade of slip, whether the level is unstable or moves on flexion-extension X-rays, how much bone and joint the planned decompression would remove, bone quality, general health, and personal goals.

Questions to ask your clinician

If you have been told you have spondylolisthesis, these questions can help you understand your own situation:

How the slip is confirmed on examination and imaging is covered in How Spondylolisthesis Is Diagnosed. Why a pars stress fracture in a younger person is not the same problem as a degenerative slip in an older adult is covered in Spondylolisthesis in Younger People and Older Adults. Day-to-day limits over a longer stretch are covered in Living With Spondylolisthesis: Long-Term Outlook.

• What type is my slip, degenerative or isthmic, and what grade is it?
• Does the slip move when I bend forward and backward?
• Is there stenosis at the same level, and does it match my symptoms?
• Which of my symptoms is the slip likely causing, and which might have another cause?
• What non-surgical options make sense for me, and how long should I try them?
• If surgery were considered, would decompression alone be reasonable, and why or why not?