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

The fracture in this small piece of bone, called the pars interarticularis, is caused by repetitive stress to the bone. The stress fracture tends to occur most commonly when an individual is young (around 5 to 17 years old) and their bones are still growing.  Some adolescents with spondylolisthesis will develop back pain, but for many people symptoms typically do not develop until adulthood.

It is estimated that 5 to 7% of the population has either a fracture of the pars interarticularis or a spondylolisthesis (slipped vertebral body), but in many cases there are no symptoms. It has been estimated that 80% of people with a spondylolisthesis will never have symptoms, and if it does become symptomatic, only 15 to 20% will ever need surgical correction.

The pars interarticularis (latin for “bridge between two joints”) connects the facet 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. There also can be a fracture of the pars interarticularis without a vertebral slip. The fracture itself is known as a spondylolysis. The pars interarticularis may also be referred to as the isthmus.

When this small bone fractures it usually does not cause pain or other symptoms. Trauma is not a common reason for fracturing. The fracture is usually due to cumulative stress, analogous to taking a paper clip and bending it multiple times. It will eventually break apart after enough stress.  Adolescents involved in different sports are prone to developing a stress fracture. 

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

A fracture has not ever been found in a newborn so it is not considered a congenital problem. The slip that results from having the fracture is most likely to progress in juvenile or adolescent individuals. Progression of the slippage in adulthood is rare.

At L5-S1 there is not usually a lot of instability associated with the condition because there is a large ligament (the sacral ala ligament) that connects the L5 vertebral body to the sacrum, preventing the progression of slippage of L5 on the sacrum.

Isthmic Spondylolisthesis Video

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 the  sacrum and into the pelvis. Fortunately, most slips are grade one or grade two, and if they become symptomatic they can be treated without 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.

In addition to the above pain-related symptoms, most patients with isthmic spondylolisthesis have tight hamstrings – the large muscle that runs down the back of the thigh – making it difficult for them to touch their toes.

Spondylolisthesis Symptoms

Grade 2 to 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.
  • Often the patient’s hamstrings will become very tight, which in turn leads to a waddling gait.

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 exceedingly 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.

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

  • Pain medications – NSAID’s and acetaminophen are good options
  • Ice and/or heat therapy – both are good options to relieve flare-ups of pain
  • Physical Therapy – Physical therapy can be useful, especially to stretch the hamstring muscles. The condition causes the hamstrings to tighten, and as they tighten they contribute to extra stress across the disc and the fracture. Stretching of the hamstrings interrupts the cycle of pain causing hamstring spasm leading to further back pain.

During adolescence, a small number of individuals will need surgical stabilization because of back pain that is unresponsive to non-surgical treatment. This, however, is unusual as in most cases the back pain will resolve with time and nonsurgical care, such as anti-inflammatory medication, gentle stretching, and physical therapy.

For a very small minority 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 (undesirable side effects and potential complications) of a spinal fusion surgery may be outweighed by the risk of progression of the deformity.

Pain from Isthmic Spondylolisthesis in Adults

An isthmic spondylolisthesis may also become symptomatic in adults, most typically when people are in their thirties and forties.

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 facet joints, the disc space is forced to withstand shear forces. Normally the facet joints in the back of the spine protect the disc from shear as they act to limit the shear force. When there is a pars interarticularis fracture the facet joints cannot limit shear. 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

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:

Medications

Pain medications, such as acetaminophen, and/or NSAID’s (e.g. ibuprofen, COX-2 inhibitors) or oral steroids to reduce inflammation in the area.

Modalities

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

Physical Therapy

Stretching is recommended, beginning with hamstring stretching and progressing over time. In addition, special attention should be paid to stretching the hamstrings twice daily in order to alleviate stress on the low back. The exercise program should be controlled and gradually increase over time.

Manual manipulation

Chiropractic manipulation, or manual manipulation from osteopathic doctors, physiatrists or other appropriately trained health professionals, can help reduce pain by mobilizing painful joint dysfunction.

Epidural steroid Injections

If the patient is having severe pain, injections can be useful. 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. The steroid can be useful to reduce inflammation in the pars interarticularis, helping to relieve the pain and allow the patient to progress with physical therapy and non-surgical treatment.

Spondylolisthesis Surgery

In most cases non-surgical treatment is successful in relieving the patient’s pain, but if not surgery may be considered.

Spinal fusion surgery for spondylolisthesis is generally quite effective, but because it is a large procedure with a lot of recovery, it usually is not considered until a patient has failed to find pain relief with at least six months focused on a range of non-surgical treatments.

A posterior fusion with pedicle screw instrumentation is generally considered the gold standard form of lumbar spinal fusion. The surgeon may also recommend a spinal fusion done from the front of the spine at the same time. 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.