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Risk Factors for Next Level Vertebral Degeneration After Spinal Fusion

Despite the efforts of doctors, physical therapists, and patients themselves, sometimes lumbar spinal fusion is inevitable. And whenever considering surgery, the benefits and disadvantages must be weighed against each other.

Fusion provides support and stability, thus reducing pain and improving function for many patients. But there's some evidence that in the long-run, the next (adjacent) vertebral level can start to degenerate. Does this affect everyone? Or are just certain people at risk for this complication?

In this study, surgeons from Seoul, Korea looked for possible risk factors. If physicians could identify who's at risk ahead of time, it might be possible to prevent this from happening. At the very least, patients would be aware of this potential problem when making the decision to have a spinal fusion.

A group of 48 men and women had an instrumented spinal fusion at L4-5. Instrumented means some type of hardware was used. Instrumentation prevents movement between the vertebrae and protects the graft so it can heal better and faster. In this study, anterior or posterior lumbar interbody fusion was done on each patient.

MRIs, CT scans, and X-rays were used to look for adjacent segment degeneration (ASD). Any one of eight criteria was used to define ASD. This included obvious disc degeneration or an angle change between the two segments. Disc herniation, spinal stenosis, bone spurs, and facet joint changes were also considered signs of ASD.

While following each patient for at least two years, data was collected on symptoms (pain, numbness, tingling, walking ability). Any other clinical signs present and recovery rate were noted. Age, gender (male or female), height and weight, bone density, and fusion length were also recorded.

The authors reported a 62.5 per cent rate of ASD. Most of the time, this was in the segment above the fused vertebra. A few patients had ASD at the level below the fusion or above and below at the same time.

Next, they looked at the differences between patients with ASD and those without ASD. They noticed that younger patients were more likely to develop degenerative changes. ASD did not appear to be linked with gender, body mass index (height or weight), or bone mineral density.

The group without ASD had better results in the first three months after surgery. But by the end of one year, there was no difference in function, success rate, or complications (except for the ASD) between the two groups.

Overall, good-to-excellent results were reported for 87 per cent of the total group (with or without ASD). Having ASD didn't necessarily mean the patient had a bad result or poor outcome. Many times the patient didn't even know this complication existed. In fact, only 6.7 per cent of the patients in this study had further surgery to fuse the next level.

The results of this study support evidence in other studies that ASD is caused by postoperative malalignment more than by mechanical factors. Mechanical factors refers to the increased stress and load transferred from the fused site to the adjacent segments. This was observed by the fact that the ASD group no longer had the same lumbar curve called lordosis that was present before the surgery. Postoperative lordosis may be related to the kneeling position of the patient on the operating table during the surgery.

And there was one final observation from this study. Patients who had anterior lumbar interbody fusion (ALIF) were less likely to develop ASD compared to those who had a posterior procedure. ALIF has the advantage of restoring normal lumbar lordosis without damaging posterior soft tissue and bony structures.

Overall, there were three statistically significant risk factors for ASD: age, lordosis, and type of fusion. It looks like older adults who have an ALIF with restoration of normal lumbar lordosis have the best chance for an excellent outcome without ASD.

Jun-Hong, Min, MD, PhD, et al. The Clinical Characteristics and Risk Factors for the Adjacent Segment Degeneration in Instrumented Lumbar Fusion. In Journal of Spinal Disorders & Techniques. July 2008. Vol. 21. No. 5. Pp. 305-309.


*Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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