Lumbar Spinal Stenosis With Grade I Spondylolisthesis

While, in many ways "bread and butter" spine surgery pathology, the optimal management for spinal stenosis with spondylolisthesis continues to be debated. I trained with the late, great Harry Herkowitz, who contributed greatly to our understanding of the role of fusion in these patients. Later, I practiced with Dr. Herkowitz and Dr. Jeffrey Fischgrund. Over short term follow-up, they found the mere attempt at stabilization improved outcomes in patients decompressed for stenosis.¹ However, when a similar population of patients was assessed over the longer term, those patients who achieved a true fusion enjoyed a better clinical result.²

I mention this background for two reasons. First, our understanding of optimal treatment and timing of that treatment continues to evolve. Second, as new technologies emerge, many initially look promising, but fail to hold up over the longer term. In the case under discussion, a wider dissection and the additional OR time required to place transpedicular instrumentation is avoided by use of an interspinous process fixation device. If this device holds up over time, it might prove to be an elegant solution for this type of low-demand individual. In this case, the follow-up interval is not enumerated. Clearly, the illustrative radiographs are from the early post-operative period.

Some of my concerns about this case relate to patient data to which I don't have access. For example, I don't see any evidence of fusion. What type of fusion was performed and with what kind of graft? I'm assuming a facet fusion with local bone was used. The same older patient with challenged physiology in whom aggressive fusion techniques are not appealing are also those patients for whom more aggressive techniques are required.

While the conclusions of various biomechanics studies vary, spinous process fixation initially made the most sense as a posterior tension band in patients undergoing anterior column reconstruction (such as an ALIF or XLIF).³˒⁴ I have a hard time imaging this type of device alone resisting shear forces.⁵

What did the patient's DEXA scan show? How well can we predict spinous process strength (especially after decompression)? How weak can the bone get before the presenter would no longer use this device? Interspinous spacer devices such as the X-STOP were introduced with some fanfare, but longer-term results have been marginal.⁶ Poor bone quality and spondylolisthesis predicted eventual failure.

Of course, spinous process fixation is different, but long-term outcomes reports are not yet available. Hopefully, this presenter and others will present long term follow-up data on large patients groups.

References
1. Fischgrund JS, et al. 1997 Volvo Award winner in clinical studies. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective, randomized study comparing decompressive laminectomy and arthrodesis with and without spinal instrumentation. Spine (Phila Pa 1976). 1997;22(24):2807-2812.

2. Kornblum MB, et al. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective long-term study comparing fusion and pseudarthrosis. Spine (Phila Pa 1976). 2004;29(7):726-733, discussion 733-734.

3. Fogel GR, et al. Biomechanics of lateral lumbar interbody fusion constructs with lateral and posterior plate fixation: laboratory investigation. J Neurosurg Spine. 2014;20(3):291-297.

4. Wang JC, et al. Comparison of CD HORIZON SPIRE spinous process plate stabilization and pedicle screw fixation after anterior lumbar interbody fusion. Invited submission from the Joint Section Meeting On Disorders of the Spine and Peripheral Nerves, March 2005. J Neurosurg Spine. 2006;4(2):132-136.

5. Yao Q, et al. Motion characteristics of the lumbar spinous processes with degenerative disc disease and degenerative spondylolisthesis. Eur Spine J. 2013;22(12):2702-2709.

6. Gazzeri R, Galarza M, Alfieri A. Controversies about interspinous process devices in the treatment of degenerative lumbar spine diseases: past, present, and future. Biomed Res Int 2014:975052.

Dr. Truumees' comments on this case are very erudite and thoughtful. It is true that long-term clinical data is not available for lumbar fusion done with interspinous devices (ISPs). Despite this, early anecdotal case reports indicate that in the low-demand elderly patient, ISPs are a very attractive alternative fixation device to pedicle screw fixation due to their ease of insertion, limited operative time, diminished blood loss, and faster recovery. That said, careful patient selection should be done to avoid using ISPs in cases that might exceed the device’s fixation limits.

The ideal candidate is similar to this patient; a low-grade slip with a collapsed disc space. This would indicate that despite a slip, there is already anterior support since the disc space has collapsed. On the other extreme, the wrong patient would be someone with a high-grade slip and large disc space with significant movement on flexion/extension radiographs.

The device used in this case is dissimilar to devices such as X-Stop, which is s a non-fusion device, and the early generation ISP that relied on true spinous process fixation. The problem with the early generation ISP, as correctly pointed out by Dr. Truumees, is the diminished bone quality of the spinous process in the elderly population on which their fixation is dependent. In contrast, the device used in this case relies on spinous-lamina fixation where the bone quality is superior.

The fusion performed in this case was a facet and posterior lamina element fusion. The advantage of this over just a facet fusion is the large surface area available for fusion.

In closing, ISPs should be considered another arrow in the spine surgeon’s quiver. As such, and with any other technology, it has limitations and advantages based on the clinical situation and therefore, should be used accordingly. The danger, as with any other instrument, is that we fail to understand this and use ISPs indiscriminately. Hopefully, as we begin to see more widespread use of ISPs, we will also begin to see more long-term studies that provide clinical information to help guide our use of ISPs.