Review and Update on Isthmic Spondylolisthesis

The topic of isthmic spondylolisthesis comes up often in the orthopedic surgeon's office. It's a condition that develops in childhood but often shows up with symptoms of low back pain in early adulthood. What is it? What can be done about it?

By definition, isthmic spondylolisthesis is the forward slippage of one vertebra over another (the one below it). It happens because there is a defect (usually a tiny crack) in the pars interarticularis (one of the supporting columns of the vertebra). That defect develops early in life before the bones are fully grown and fused.

The last lumbar vertebra (L5) is the one most likely to slip forward (over the sacrum, S1). But isthmic spondylolisthesis can develop anywhere in the lumbar spine, particularly at the L4-L5 or L3-L4 levels.

It's not something we know how to prevent, so most medical efforts are on the treatment side of things. The type of treatment recommended depends on the grade of the slippage. Low-grade spondylolisthesis means up to 50 per cent of the vertebral body has shifted forward. A shift forward of more than 50 per cent is classified as a high-grade slippage.

Studies have confirmed that the natural history of isthmic spondylolisthesis (i.e., what happens over time) has a very low incidence of progression. In other words, it stays the same and doesn't get worse over time. Most cases of spondylolisthesis can be treated conservatively (without surgery). This is especially true for the low-grade type.

Conservative (nonsurgical) care involves physical therapy, activity modification, and sometimes bracing and/or pain relieving medications. Physical therapists teach the patients lifelong skills of management including core training, correct posture and lifting, stretching, and aerobic conditioning.

Surgery is considered under several conditions: 1) the patient does not improve with conservative care, 2) there is a high-grade slippage or a low-grade spondylolisthesis that is quickly progressing to a high-grade status, 3) pressure on the spinal nerve roots is causing significant pain, numbness, and/or weakness that hasn't responded to conservative care.

That all sounds so easy to figure out -- and for the most part, it is a treatment protocol that works well. What isn't easy to decide on is the type of surgery required. Considerable debate and controversy exists among orthopedic surgeons over this topic. What's the latest thinking here?

There are half a dozen surgical procedures that can be done. These range from simply removing bone from around the compressed nerve root to full reduction of the slip and total fusion of the spine at the affected level. And then there are an equal number of ways to perform the fusion procedure, so choosing the right one for each patient can be a challenge.

Children (pediatric cases) have to be handled differently from adults because they have not reached full skeletal maturity. So long as the bones are still growing and changing, surgery can't be the same as it is for adults. Imaging studies such as X-rays can be helpful to the surgeon when deciding what to do and how to do it.

One of the big decisions is whether to 1) try and correct the slippage (called reduction), 2) reduce and then fuse that spinal segment in place, or 3) fuse it where it is (slipped forward). This decision is made based on patient age and symptoms (especially the presence of pain and/or nerve compression). The presence and severity of any postural deformities that have developed must be considered. And surgeon experience will also tend to dictate the type of surgery recommended.

Each of these surgical approaches has its pros and cons. Reduction is easier in children who are still more flexible and in whom the postural deformities haven't become permanent. With severe slippage, fusion holds better if reduction can be done first.

But there are risks with reduction -- the technique of shifting the slipped vertebra back where it belongs often causes injury or damage to the spinal nerve root nearby. If the surgeon is concerned about this complication, then a partial reduction might be done instead.

The decision regarding how to perform a fusion procedure presents its own unique challenges. The surgeon must decide whether to use an anterior approach (from the front of the spine) or posterior approach (from the back). Other options include somewhere in between (anterolateral or posterolateral) or circumferential (all the way around) fusion.

The use of metal plates, screws, pins, and type of bone graft material are additional considerations. Surgeons rely on personal experience (tracking their own patients' results) along with reports in the literature about successful outcomes with each type of surgical approach. This information is evaluated separately for the pediatric and adult groups with this condition.

If you aren't too dizzy thinking about all the decisions the surgeon must make when planning surgical treatment for severe slippage, please consider one more thing. The type of approach and method of fusion also depend on what spinal level is being corrected. Reduction and fusion surgery is different at L4-5 than it is at L5-S1. With an L4-5 correction, it's one lumbar vertebra fused to another. With L5-S1, the last lumbar vertebra is being fused to the top or dome of the sacrum.

The authors of this review provide much to think about in the treatment and management of isthmic spondylolisthesis at all ages. Conservative care is the first line of treatment in most cases (children and adults) unless the slippage is severe and symptomatic.

Surgical treatment is not standard (there isn't one procedure that fits all patients). With time and the results of ongoing studies, surgeons will find what works best for each patient based on grade, age, severity, and other significant factors. Review articles like this one from the North American Spine Society (NASS) will help keep surgeons up to date on the latest results in research.

Reference: 

Steven S. Agabegi, MD, and Jeffrey S. Fischgrund, MD. Contemporary Management of Isthmic Spondylolisthesis: Pediatric and Adult. In The Spine Journal. June 2010. Vol. 10. No. 6. Pp. 530-543.

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