Decompression and Coflex interlaminar stabilization compared with decompression and instrumented spinal fusion for spinal stenosis and low-grade degenerative spondylolisthesis: two-year results from the prospective, randomized, multicenter, Food and Drug Administration Investigational Device Exemption trial.
Purpose of Study
By most definitions, this is a good example of a randomized control trial (RCT). The study populations were well matched and the outcomes were standardly measured. The follow-up rate was greater than 80%.
The inclusion criteria included the presence of back pain (VAS of 5/10 or more), along with spinal stenosis and up to grade I spondylolisthesis from L1-L5 for one and two levels.
The selection criteria has one factor that allowed subjectivity to enter into the selection. The radiographic definition of spinal stenosis was not well defined, and not all findings were necessary to include into the study.
In terms of the results, it is not an unexpected outcome when comparing the length of stay, narcotic use, blood loss, and time of surgery.
The insertion of the Coflex device after central and foraminal decompression adds very little additional dissection compared to the standard decompression. The authors comment on the difference in exposure compared to the standard posterolateral fusion. There is no need to expose the facet joints or the transvers processes. This fact alone should demonstrate a significant reduction in surgical time, post operative pain, and length of stay. To make a comparison, studying the difference in blood loss, operative time, post operative pain and length of stay from lumbar laminectomy vs lumbar laminectomy and fusion probably will yield similar results to lumbar laminectomy and coflex vs. laminectomy and fusion.
This study does demonstrate non inferiority of the decompression/Coflex group compared the decompression/Fusion group. Both groups achieved equivalent survival (success) rates at 2 years.
The study measured the range of motion at the operative levels as well as the range of motion of the adjacent levels. The authors suggested there was a trend to increased flexion-extension range of motion at the superior and inferior range of motion in the fusion population compared to the Coflex population. Review of the data (table 9) did not indicate the measurement changes were statistically significant.
While the authors hoped to demonstrate the motion preservation nature of the coflex device, and protection from adjacent level disease associated with lumbar fusion, this was NOT demonstrated in the study.
In terms of statistical significance, the Coflex population had improvement in the ZCQ in terms of symptoms, physical function and satisfaction compared to the fusion group. While the statistics may be significant, there are issues related to the unblinding of the two groups. In addition, the difference may be secondary to the exposure required for the fusion versus the less tissue dissection for the Coflex group.
The duration of followup is only two years, and longer term studies may demonstrate other advantages of one surgical technique over the other. A better study may be to compare patients with spinal stenosis and back pain without spondylolisthesis and compare decompression/Coflex with decompression/fusion.
On comparing spinal stenosis with grade 1 spondylolithesis patients randomized to the two treatment groups. The narrowness of the criterion may make it difficult to achieve the statistical power, but these would be better RCT’s.
The more clinically relevant study would be to compare lumbar laminectomy vs lumbar laminectomy and coflex in a population of patients with clinically significant spinal stenosis without spondylolisthesis. The surgical dissection would be very similar. The main difference would be the addition of the device. In the long term, we would know if the device would help protect from post laminectomy instability.
In general this is a good study showing the equivalence of two year outcome for patients who have lumbar spinal stenosis from L1-L5 with back pain and up to grade I spondylolisthesis when comparing Coflex to fusion. As always, the study could help identify further studies that can identify the potential advantage of intralaminar stabilization for lumbar spinal stenosis patients.