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Updated: Nov 26, 2020

The spine condition called isthmic spondylolisthesis occurs when one vertebral body slips forward on the one below it because of a fracture in a piece of bone that connects the two joints on the back side of the spine.

The fracture in this piece of bone, called the pars interarticularis, is caused by stress to the bone. While the fracture tends to occur most commonly when an individual is young, for most people symptoms typically do not develop until adulthood. There is another spike in occurrence of lower back pain from spondylolisthesis in adolescence.

It is estimated that 5 to 7% of the population has either a fracture in this small piece of bone (a fracture of the pars interarticularis) or a spondylolisthesis (slipped vertebral body), but in most cases there are no symptoms.

Spondylolisthesis Causes

The pars interarticularis (latin for "bridge between two joints") connects the vertebral joint above to the one below. It is a thin piece of bone with a poor blood supply, which makes it susceptible to stress fractures.

Isthmic spondylolisthesis occurs most commonly in the L5-S1 level of the spine, the lowest level of the lumbar spine. It does happen rarely above this level, at L4-L5 or L3-L4, but at these levels trauma (rather than cumulative stress) is a more common cause of the fracture.

Spondylolisthesis Grading

The severity of the slippage is usually measured after taking a side-view X-ray, and then graded on a scale of 1 to 4. The slippage is measured from the amount the upper vertebral body slips forward on the lower vertebral body.

Grade 1  

  25% or less of vertebral body has slipped forward

Grade 2  

  26% - 50%

Grade 3  

  51% - 75%

Grade 4  

  76% - 100%

Although very rare, a condition called spondyloptosis can occur, whereby the L5 vertebral body slips off completely into the pelvis. Fortunately, most slips are grade one or grade two, and if they become symptomatic they can be treated with surgery.

Isthmic Spondylolisthesis Symptoms

For patients with symptomatic isthmic spondylolisthesis, the most common symptoms include:

  • Low back pain, often described as a deep ache in the lower back

  • Pain that radiates into the buttocks and back of the thighs, (also called radicular pain)

  • Pain that is worse when standing, walking, or any type of activities that involves bending backwards

  • Pain that feels better with sitting, especially sitting in a reclining position

  • A tired feeling in the legs, and possibly leg numbness or tingling, especially after walking

  • Pain that radiates below the knee and possibly into the foot.

Grade 2, Grade 3, Grade 4 Spondylolisthesis Symptoms

In addition to the above symptoms, patients with a grade two or higher slippage usually have a fairly recognizable deformity to their low back, especially if the slip is accompanied by a very vertical angle. For example:

  • The patient will appear to have a short trunk and a large abdomen.

  • He or she will have an accompanying large lordosis (sway to the low back), and a vertical pelvis.

Rarely, patients may also have symptoms of cauda equina syndrome, such as progressive numbness or weakness in the legs, altered sensation in the saddle area between the legs, and difficulty controlling the bowl and/or bladder. If such symptoms are present, the patient should seek emergency medical attention.

Isthmic Spondylolisthesis During Adolescence

Isthmic spondylolisthesis is a common cause of back pain in adolescents. It is suspected that spondylolysis (the fracture in the lower back that can lead to spondylolisthesis), occurs most frequently in young athletes who are involved in sports that involve repeated hyperextension of the lower back (bending backwards), such as gymnastics.

The most common symptom is back and/or leg pain that limits a patient's activity level. In cases of a more advanced slip, such as a grade 2 or more spondylolisthesis, the patient may have a noticeable forward curve or sway back in their lower back. Development of either neurological problems or paralysis is possible but fortunately rare.

Adolescent Spondylolisthesis Treatment

Adolescents involved in sports can develop back pain from their activity. If a spondylolisthesis is noted on x-ray, generally it is recommended that the athlete refrain from sports until he or she is free from pain after his fracture is fixed with a Spinal Fusion Surgery.

For a majority of adolescents, if they develop a grade two or more spondylolisthesis that is symptomatic, surgical stabilization with a spinal fusion is generally recommended to prevent further progression of the slip. Unlike spondylolisthesis in adults, in adolescents it is more likely that the slip may progress, and the morbidity of a spinal fusion surgery may be outweighed by the risk of progression of the deformity.

The typical range of non-surgical treatments may be employed to manage pain before or after surgical fixation, including:

  • Pain medications - NSAID’s and acetaminophen are good options

  • Heat therapy – both are good options to relieve flare-ups of pain

  • Physical Therapy - Physical therapy is strictly contraindicated and minimal manipulation of the spine should be attempted before the unstable fracture has been fixed surgically. Performing exercises or stretching in an unstable spine can actually lead to progression of the instability and can lead to paralysis of both the limbs.

Pain from Spondylolisthesis in Adults

An isthmic spondylolisthesis may become symptomatic in adults, most typically when people are in their 30s and 40s.

How Spondylolisthesis Causes Pain

There are two primary forces at work with isthmic spondylolisthesis in adults.

Disc Degeneration

The most common reason for low back pain in this situation is that the disc will start to wear out. Without a posterior tether connecting the vertebral joints, the disc space is forced to withstand shear forces. Discs work well as a shock absorber but they are susceptible to being damaged if they have to resist shear. The associated cumulative stress leads the disc to breakdown and eventually become painful.

Nerve Pinching

As the discs break down, they become flatter and the disc provides less room for the nerve root to exit the spine (e.g. the L5 nerve root at L5-S1 level) and the patient can develop leg pain (radiculopathy, or sciatica). It is common for the leg pain to be related to walking or standing as in these positions the foramen (the opening where the nerve exits the spine) is closed down. When sitting the foramen is larger and eliminates the pressure on the nerve. However, the converse may also be true, as in the sitting position the disc is loaded three times more than when standing, and the loaded disc can bulge into the foramen causing leg pain.

Spondylolisthesis Treatment

For a majority of patients, if they develop spondylolisthesis that is symptomatic, surgical stabilization with a spinal fusion surgery is generally recommended to prevent further progression of the slip. In adults if it is left untreated, then instability may lead to further progression of the slip which can lead to more serious consequences like paralysis of both legs or loss of control of urine or faeces.

Non-surgical treatment is usually reserved just to provide temporary relief to the patients before or after the surgery. There is no role of Non-Surgical treatment as the complete or definitive treatment for Spondylolisthesis. Non-surgical treatment for adult patients with an isthmic spondylolisthesis is similar to that for patients with low back pain and/or leg pain from other conditions and may include one or a combination of:


Pain medications, such as acetaminophen, and/or NSAID’s (e.g. ibuprofen) or oral steroids to reduce inflammation in the area.

Heat and/or ice application

Generally, ice is recommended to relieve pain or discomfort directly after an activity that has caused the pain. Applying heat is recommended to relax the muscles, and promote blood flow and a healing environment.

Physical Therapy

Physical therapy is strictly contraindicated and minimal manipulation of the spine should be attempted before the unstable fracture has been fixed surgically. Performing exercises or stretching in an unstable spine can actually lead to progression of the instability and can lead to paralysis of both the limbs.

Manual manipulation

Strictly contraindicated – may harm the patient

Epidural steroid Injections

If the patient is having severe pain, injections can be useful as a temporary measure. Epidural injections can help decrease inflammation in the area. The pars fracture itself can be injected with lidocaine and steroids for a diagnostic study. If the patient’s pain is relieved after a lidocaine injection it can be assumed that the pars fracture is the source of the patient’s pain.

Spondylolisthesis Surgery

In most cases, surgical treatment is the only treatment option and is successful in relieving the patient’s pain in more then 90% of the patients with Spondylolisthesis.

A posterior fusion with pedicle screw instrumentation is generally considered the gold standard form of lumbar spinal fusion.The type of spinal fusion that is recommended by a surgeon is based largely on a surgeon’s preference and experience, as well as the patient’s clinical situation.