Problems with Adjacent Spinal Segmental Degeneration After Lumbar Fusion
More and more older adults with chronic lumbar pain are having spinal fusion to treat the problem. As a result, surgeons face new problems to deal with. For example, once a moving spinal segment is fused, the load on the other (adjacent) segments increases. The result may be adjacent segment degeneration (ASD).

But it's not clear yet if these changes cause clinical problems. The changes can be seen on X-rays. The question is: do they cause painful symptoms or loss of function? In this study, patients treated with L4-L5 or L5-S1 fusion are observed for many years after the surgery. Periodic X-rays and clinical exam were performed.

Their pain levels, function, and satisfaction are measured and tracked over the years. Disc space height, movement of the vertebrae, and angle of the lumbar spine alignment were also calculated or assessed.

Follow-up results showed that patients with a L5-S1 fusion had fewer cases of ASD. Fusion at the L4-L5 level seemed to result in a greater risk of ASD. If the fusion was done at the level of the stable sacral base, then there was a trend toward fewer cases of ASD. Fusions at the L4-L5 level called floating fusions were more likely to develop ASD.

The rate of ASD did not seem to depend on the way the surgery was performed. There were two different methods for fusing the lumbar spine used in this study. A detailed description of approach, operative strategy, and postoperative program used for these patients was included for the readers.

Important factors affecting the outcome of the procedure included the angle of the sacrum and the age of the patient. Younger patients (less than 45 years old) were less likely to develop ASD. A more vertical angle of the sacrum was accompanied by higher rates of ASD. The type of surgery performed did not seem to make a difference.

The results of this study confirm what other studies have shown. Stress and shear forces increase on adjacent spinal segments after spinal fusion. The level above the fusion is subjected to the most changes.

Newer procedures using cage devices in between the vertebrae to correct the sacral angle may have better results. But even with these implants, there is concern about early degenerative changes seen on X-rays at the adjacent segments.

However, it's not clear if changes observed on X-rays translate to increased painful symptoms and loss of function clinically. Re-operation isn't necessarily the next step when ASD occurs. More studies are needed to identify predictive factors for successful outcome of fusion. This could help predict which patients are good candidates for lumbar spinal fusion with lower risk of ASD.
Alexander Carl Disch, MD, et al. Higher Risk of Adjacent Segment Degeneration After Floating Fusions: Long-Term Outcome After Low Lumbar Spine Fusions. In Journal of Spinal Disorders & Techniques. April 2008. Vol. 21. No. 2. Pp. 79-85.