Optimal End Level for Long-Segment Cervical Fusion to the Thoracic Spine?

Peer Reviewed

Extending posterior cervical fusions for degenerative spine conditions into the thoracic spine is associated with less risk for pseudarthrosis but significantly greater blood loss and a tendency toward greater operating room time and length of hospital stay, according to a multicenter retrospective analysis published in the May issue of The Spine Journal.

“We started this study because my partners and I had all been taught very different things about the ‘right’ end level for a long, posterior cervical fusion,” explained lead author Eeric Truumees, MD, Professor of Orthopaedic Surgery at The University of Texas Dell Medical School, and CEO of the Seton Brain and Spine Institute, both in Austin, TX. “Those varied from ‘avoid crossing the cervico-thoracic junction’ to ‘you always have to go to T4.’ The argument, as with the thoracolumbar junction, involves the ‘rigid thoracic spine.’ But, we know that T1-T3 exhibit quite a bit of motion (as do the lower thoracic vertebrae).”

cervical and thoracic spinal columnExtending cervical fusion into the thoracic spine may be preferable in select patients.

“As we did our literature search, we found that there was little high-level support for the recommendations made,” said Dr. Truumees, who is a member of the SpineUniverse editorial board. “Ultimately, we found that the benefits of extension into the thoracic spine were mixed. At least at this point, the data do not justify a hard and fast rule.”

The researchers examined prospective collected radiographic and clinical data from 177 adult patients who underwent three or more levels of posterior cervical fusions for degenerative disease between January 2008 and May 2013. Patients were categorized into two groups based on whether the cervical fusion ended in the cervical spine (Group 1; n=104) or extended into the thoracic spine (Group 2; n=73).

Groups Showed Similar Clinical and Radiographic Outcomes
The groups showed similar improvement in cervical lordosis post-operative as well as change or maintenance in change or maintenance of mean cervical lordosis (at 2 weeks compared with 2 years post-operatively). Likewise, change in mean C2–C7 sagittal plumb line and T1 slope as well as significant changes in visual analog scale and Oswestry Disability Index (ODI) was similar in the two groups.

In contrast, the groups showed significantly differing outcomes in relation to pseudarthrosis rate, with higher rates found in Group 2 (21.2% vs 10.96%; Table). Additional differences were found in mean estimated blood loss (higher in the extension group) as well as mean operating room time and length of stay (both slightly higher in the extension group; Table).
Table. Outcomes of Posterior Cervical Fusion by EndpointOutcomes of posterior cervical fusion by endpoint.Future Research May Help Predict Optimal End Levels
“We are in the middle of a much larger study to better assess the impact of patient-specific factors such as bone quality and sagittal balance on optimal end levels,” Dr. Truumees said. “The current data revealed lower pseudarthrosis rate, but greater blood loss and longer operating room times when the fusion was carried into the thoracic spine. With this in mind, stopping at C7 is justified in those patients at lower risk for pseudarthrosis, or those for whom additional blood loss and operative time would be poorly tolerated.”

For example, extension of surgery to the thoracic spine may be preferable “in smokers and other patients at increased risk for pseudarthrosis, as well as in patients with anatomical limitations to strong C7 bone anchorage,” the authors wrote.

“I think we all see certain conditions in which routine extension of a cervical fusion to the thoracic spine makes sense,” Dr. Truumees concluded. “In a revision context, new or previously undiagnosed C7-T1 spondylolisthesis is not uncommon and therefore should be closely sought ahead of an index surgery. Another frequent issue is poor quality fixation in the C7 lateral masses. If C7 pedicle fixation cannot be achieved and the lateral masses are weak, extension to the thoracic spine makes sense. Personally, I have a sense that a number of other, particular situations will favor routine thoracic extension, but the confirmatory data is not yet available.”

Commentary

Saad B. Chaudhary, MD, MBA
Minimally Invasive & Complex Spine Surgery
The Mount Sinai Hospital
Associate Director, Spine Surgery Fellowship
Assistant Professor
Department of Orthopaedic Surgery
Icahn School of Medicine at Mount Sinai

This is an important topic with a paucity of high level scientific evidence available for decision making. Much like the debate of stopping a fusion at the lower lumbar spine version extending a fusion into the sacrum, there are pros and cons to each approach.

The following are key takeaway points from the study:

  • Clinical improvement using the visual analog scale and Oswestry Disability Index was found in both groups compared to baseline, and no significant difference was found clinically between the two groups.
  • No significant difference exists with regards to restoring or maintaining cervical alignment with either a lower cervical fusion endpoint or a thoracic endpoint. This was also true of more regional alignment parameters such as the sagittal plumb line and T1 slope. In future studies, it may be helpful to look at full length spine films to assess global sagittal balance as well.
  • Not surprisingly, extension into the thoracic spine took slightly longer and resulted in more blood loss. However, it is not indicated whether the increase in blood loss required any additional treatment including a transfusion.
  • The single most valuable and somewhat surprising finding was that terminating the fusion in the lower cervical spine resulted in approximately twice as high a rate of non-union when compared to the posterior cervico-thoracic fusion (10.96% vs. 21.2%). This is different than the issue at the lumbosacral junction, where crossing the junction into the sacrum usually results in the opposite effect of an increased non-union rate.

This last point can help most surgeons decide on the caudal most level for instrumentation and fusion. Patients with a high risk for non-union would benefit from extension of their surgery into the thoracic spine. Some patient-related risk factors to consider when deciding on a posterior cervical fusion versus posterior cervical fusion with extension into the thoracic spine are smoking history, diabetes, and bone quality, etc. Although, osteoporosis is not a direct risk factor for pseudarthrosis, it is critical to consider the patient’s bone quality when instrumenting, as a poor lower cervical anchor point would likely result in hardware failure and perhaps a non-union.

In my clinical practice, almost all patients who require a long (≥3 segments) posterior cervical laminectomy and fusion get extended into the proximal thoracic spine, typically down to T1 or T2. The main reason is that majority of the patients that receive this surgical option in my hands may either require a decompression at the C7-T1 junction or have risk factors that would either result in cervico-thoracic junctional degeneration or anatomically have an inadequate anchor point at C7. Furthermore, this study had a very large number of patients who had a combined anterior and posterior approach (47%) when they stopped at the lower cervical spine. Contrarily, in my practice, the vast majority of these patients (>90%) only get a single approach posterior surgery, unless they have a large and rigid deformity, which may require a 360° approach.

There are a few important critiques to keep in mind while reading this study. One major point is that this is a retrospective review that follows this patient population for a limited time frame. Although, the authors had a very good (95%) 2-year follow-up, degeneration and or breakdown at the cervico-thoracic junction may take longer than their study time period. Furthermore, plain radiographs are usually not considered the best imaging modalities to visualize the cervico-thoracic junction. It may be difficult to adequately assess all the failures as well as fusions and non-unions with radiographs alone. A CT-based study may be more beneficial for all the relevant endpoints including alignment, lordosis, and fusion rate. Ultimately, if the surgical area heals and fuses appropriately, it appears that both radiographic and clinical outcomes are good whether the fusion ends at the lower cervical spine or upper thoracic spine. This underscores the importance of appropriate patient selection and tailoring surgical care and treatment with each individual patient’s physiology and functional goals in mind.

Disclosure
Dr. Truumees has no relevant disclosures.

Updated on: 07/12/18
Continue Reading
Do Multilevel Posterior Cervical Fusions Extended to T1 Reduce Revision Surgery Risk?
Eeric Truumees, MD
Professor of Orthopaedic Surgery
University of Texas Dell Medical School
Austin, TX
Saad B. Chaudhary, MD, MBA
Assistant Professor
Department of Orthopaedic Surgery
Icahn School of Medicine at Mount Sinai
New York, NY
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