Update on Current Spine Literature

Matthew L. Goodwin, MD, PhD and Brandon D. Lawrence, MD review current research in Spine

16 October 2020

We return this quarter with a review of the “best” spine articles that are published out of the Global Spine Journal, Spine, European Spine Journal and Journal of Neurosurgery Spine. These four journals, free to AO Member Plus members, are available on the AO website, and will receive a summary of a handful of articles we have selected worthy of note.  These selected articles will vary, but hopefully will call the reader’s attention to new or pertinent studies in the area of spine surgery.  This quarter we highlight five areas of interest that address a few of the most pertinent who, what, when, whereand why questions in spine surgery today:

1) Who needs a PSO at L5 (instead of the more common L3 or L4)? 2) What implant should be used when addressing adjacent segment disease (ASD) after an ACDF, a stand-alone cage or a traditional anterior plate construct? 3) When should the patient with hip and spine pathology undergo spine surgery? 4) Where should the surgeon look when trying to evaluate bone quality before instrumentation – the DEXA or CT?  And finally, 5) Why do some patients undergoing indirect decompressive surgery via anterior or lateral techniques need traditional posterior decompression as well?

First, our understanding of the profound effect of sagittal balance on patient outcomes continues to grow with the publication from Pizones et al. and the European Spine Study Group (ESSG).1  In this study, who needs a PSO is evaluated.  One hundred and twenty six deformity patients from the ESSG multicenter database who had undergone a single level lumbar PSO were included.  While L3 and L4 have been relatively common sites for PSOs over the last decade, this paper demonstrates how lumbar PSOs at these levels negatively affect the lordosis distribution index (LDI; L4-S1/L1-S1), now known to be an important parameter in sagittal balance.

In 70% of the cases with PSOs at L4 or higher, the apex of the lumbar lordosis was shifted more rostral.  L5 PSOs, in contrast, moved the lumbar lordosis apex more caudal in 70% of cases.  Using this in combination with consideration of the Roussouly-type of spine and the other “classic” sagittal balance parameters (PI, LL, SS, PT) may better determine who would benefit from an L5 PSO and more effectively balance the distribution of lumbar lordosis in hopes of improved outcomes in adult spinal deformity patients.

Next, Gandi et al.2 analyzed all ACDFs performed for adjacent segment disease (ASD) in a two year period at a single institution to determine what implant was appropriate.  When approaching ASD after a previous ACDF, what implant to  use is evaluated as surgeons need to decide whether to remove the old plate or use a stand-alone method to address the adjacent segment.  In this analysis, fusion rates for ASD in general (stand alone or plate) where lower than the index ACDF (74% vs 95%).

Fusion rate of stand-alone cages for ASD was 69%, while using the anterior plate construct for ASD was 82%.  This was not significant (likely because it appears underpowered), but it is worth noting that all four patients that returned to the OR after their ASD surgery were patients with stand-alone cages.  Often used for ASD surgeries, the stand-alone cage is thought to decrease OR time and limit EBL.  Here, however, EBL and OR time were nearly identical, raising questions about its usefulness in this setting.

Next, we turn our attention to when the patient with hip and spine pathology should undergo surgery for each – should the hip or spine pathology be addressed first?  Yang et al.3 analyzed over 85,000 patient records spanning 10 years and compared four groups of hip-spine patients: 1) patients undergoing total hip arthroplasty (THA) without spine pathology, 2) those with remote (>2 years) spinal fusions that underwent THA, and those with both hip and spine pathology who underwent either 3) THA then lumbar spine fusion (LSF), or 4) LSF then THA.  Previous reports have proposed that LSF should precede THA in the setting of hip and spine pathology, as this allows the hip surgeon to place the cup in the “safe zone” to avoid dislocation.

Now, Yang et al.3 adds to this growing literature by demonstrating that those who underwent THA before LSF had the highest rates of dislocation and revision.  Of note, however, is that those same patients also had higher rates of prosthetic joint infections, surgical site infections, and opioid use post-operatively, suggesting that the ordering of hip and spine surgery may actually be more than just the biomechanical problem of placing the cup in the safe zone.  Of course when counseling patients with concurrent disease, one pathology usually demands attention first.  Nonetheless, for those patients who truly have both, proceeding with the spine surgery first seems reasonable based on this study but does conflict with other published data.  Clearly, more studies are needed in order to better understand these complex relationships and their underlying mechanisms.

The next study evaluates where the spine surgeon should look when trying to evaluate bone quality before instrumentation – the DEXA or CT?  This is quite a complex issue, especially as it relates to adult spinal deformity and/or patients with significant spondylosis as their DEXA scans often over-quantify bone density.  The article by Zou et al.4 attempts to address this by evaluating 253 patients whom are ≥ 50 years and undergoing pedicle screw fixation for lumbar degenerative disease.

At 12 months the overall loosening rate of pedicle screws was 30.6% with the osteoporotic group, as expected, having significantly higher numbers (39.3% vs. 25.8%, P = 0.026).  The area under receiver operating characteristics curve (AUC) of predicting screw loosening was 0.666 (P < 0.001) for Hounsfield units and 0.574 (P = 0.062) for T-score.  Even though this study shows no difference in outcomes between the two groups it is nonetheless another confirmation that we can, and probably should, use CT scans to better understand the state of our patients bone density. In so doing, we can optimize our spinal instrumentation techniques and offer more predictable expectations following spine surgery.

Finally, why do some patients undergoing indirect decompressive surgery via anterior or lateral techniques need traditional posterior decompression as well? At present, there are no clear clinical and/or radiographic parameters that guide when an indirect decompression is enough. Given the high rates (up to 60%) of additional posterior laminectomy after indirect decompression this has become an increasingly relevant topic.  In this study by Park et al.5 they attempt to elucidate this important question by evaluating 86 patients, 62 of whom underwent posterior decompression after initial anterior lumbar interbody fusion (ALIF) or lateral lumbar interbody fusion (LLIF) and 24 patients who did not require posterior decompression.

The group that underwent posterior decompression showed statistically different numbers of treated segments (1.92 vs 1.21, p < 0.01), preoperative VAS leg score (7.9 vs 6.3), symptom duration (14.2 months vs 9.4 months), postoperative disc height improvement (61.3% vs 96.2%), postoperative foraminal height improvement (21.5% vs 32.1%), postoperative foraminal area improvement (24.1% vs 36.9%), and cage height minus preoperative disc height (5.3 mm vs 7.5 mm) compared with the indirect decompression group. Given that there were no pre-operative significant differences in age, sex, preoperative VAS score for back pain, cage height, cage angulation, preoperative disc height, foraminal height, foraminal area, central canal diameter, foraminal area and facet joint degeneration (p > 0.05), it appears that the foraminal measurements, and not the central canal measurements, are key to predicting who will require a formal posterior decompression versus not.

We at AO Spine hope that you enjoy these articles.  Please look forward to what we are reading in Quarter 3 of 2020! 

References:

  1. Pizones J, Moreno-Manzanaro L, Perez-Grueso FJS, et al. Effect of lumbar pedicle subtraction osteotomy level on lordosis distribution and shape. Eur Spine J 2020;29:1388-1396.
  2. Gandhi SD, Fahs AM, Wahlmeier ST, et al. Radiographic fusion rates following a stand-alone interbody cage versus an anterior plate construct for adjacent segment disease after anterior cervical discectomy and fusion. Spine 2020;45(11):713-717.
  3. Yang DS, Li NY, Mariorenzi MC, et al. Surgical treatment of patients with dual hip and spinal degenerative disease. Spine 2020;45(10):E587-E593.
  4. Zou D, Sun Z, Zhou S, Zhong W, Li W. Hounsfield units value is a better predictor of pedicle screw loosening than the T-score of DXA in patients with lumbar degenerative diseases. Eur Spine J. 2020 May;29(5):1105-1111
  5. Park D, Mummaneni PV, Mehra R, Kwon Y, Kim S, Ruan HB, Chou D.  Predictors of the need for laminectomy after indirect decompression via initial anterior or lateral lumbar interbody fusion. JNS Spine.Volume 32: Issue 6 (Jun 2020): Pages 781-987

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