Letter to the Editor: Screw fixation technique

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  • University of Pittsburgh School of Medicine, Pittsburgh, PA
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TO THE EDITOR: With great interest we read Mendes et al.’s1 description of a technique for anterior, endonasal atlantoaxial fixation (Mendes GAC, Dickman CA, Rodriquez-Martinez NG, et al: Endoscopic endonasal atlantoaxial transarticular screw fixation technique: an anatomical feasibility and biomechanical study. J Neurosurg Spine 22:470–477, May 2015). We have placed a single lag screw into the occipital condyle through an anomalous C-2 lateral mass in the setting of basilar invagination but never across a normal C1–2 facet. The technique is intriguing and indeed may be useful for some patients in providing increased biomechanical stability in association with posterior fixation or even acting alone to provide arthrodesis.

However, a few significant issues will need to be overcome. The authors appropriately noted the significant limitation of current instruments and required a custom-made 45° angled screwdriver. They described their exposure as allowing them to access the C1–2 articular surface for decortication and autograft placement. In our experience with approximately 35 patients, the upper C-1 anterior arch was easily accessed, but C1–2 was not, except in the setting of basilar invagination. In these patients, the additional problem of anterolisthesis of C-1 on C-2 significantly complicated the technique described. In a cadaver, surgical access tends to be slightly greater than in living patients, perhaps because of craniocervical settling and shrinkage of the nasopharyngeal mucosa.

Intraoperatively, limited caudal access usually makes it difficult to visualize the C1–2 joint and nearly impossible to perform debridement of the joint and bony fusion. That said, many patients with chronic C1–2 instability already have some degree of pseudarthrosis, and elderly patients may not be amenable to 2 procedures. Therefore, a single approach, even if it only provides decompression and instrumentation without fusion, may be all that can be tolerated and will at least provide some option for these patients.

In describing their approach, they mention the performance of a sphenoidotomy. This step is unnecessary for a typical transodontoid approach (though originally described) and is only needed if there is severe platybasia with the dens invaginated behind the flattened clivus. If this additional room is needed for instrumentation, it would be useful to hear the authors comment on this.

Finally, the potential for injury to the vertebral artery is discussed, but aberrant internal carotid artery anatomy (dolichoectasia) is more common in the elderly and needs to be evaluated (CT angiography) prior to any anterior approach to the craniovertebral junction.

This technique does hold great promise. It is unlikely that the “clean contaminated” concerns with endonasal access will be an issue any more than in intradural surgery, but the risk of infection with retained hardware needs to be addressed. We look forward to further reports on the technique and the development of appropriate instrumentation. We applaud the authors for their anatomical knowledge, ability, and creativity in creating this technique.

Reference

1

Mendes GAC, , Dickman CA, , Rodriquez-Martinez NG, , Kalb S, , Crawford NR, & Sonntag VKH, : Endoscopic endonasal atlantoaxial transarticular screw fixation technique: an anatomical feasibility and biomechanical study. J Neurosurg Spine 22:470477, 2015

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  • Barrow Neurological Institute, Saint Joseph’s Hospital and Medical Center, Phoenix, AZ
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Response

We appreciate the comments of Drs. Gardner, Fernandez-Miranda, Snyderman, and Wang regarding our recent paper. Their significant practical experience will further the development of the anterior transarticular technique.

A limitation of our study is the normal craniovertebral junction anatomy of the cadaveric specimens. We learned that the placement of anterior transarticular screws was feasible in this setting; however, we have not yet attempted our technique in live surgery. We hypothesize that this technique could be applied in select cases when preoperative planning studies suggest that the C1–2 lateral masses line up in the appropriate anterior-to-posterior and cranial-to-caudal trajectory.

We would like to address several comments made by the Pittsburgh team. First, performing a sphenoidotomywas helpful in increasing surgical freedom and improving manipulation of the angled instruments and screws. Second, regarding access to the C1–2 joint for arthrodesis, one might consider supplementing the endonasal exposure with a transoral corridor to achieve more caudal access and facilitate decortication of the joint. Third, their comment about the potentially problematic anatomy of the carotid artery is particularly apt, and we agree that its course should be evaluated prior to considering the application of this surgical technique.

As we stated in our report, the proposed anterior transarticular technique is not meant to replace the posterior approach, which has demonstrated value. Our group, under the leadership of Drs. Volker Sonntag, Curtis Dickman, and Neil Crawford, has played an important role in advancing posterior fixation of the craniovertebral junction. We hope that our new technique will not only give clinicians another option for select patients but also ultimately improve the safety and morbidity of patients with disease treated in this challenging region.

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Contributor Notes

INCLUDE WHEN CITING Published online July 10, 2015; DOI: 10.3171/2015.3.SPINE15244.

DISCLOSURE The authors report no conflict of interest.

  • 1

    Mendes GAC, , Dickman CA, , Rodriquez-Martinez NG, , Kalb S, , Crawford NR, & Sonntag VKH, : Endoscopic endonasal atlantoaxial transarticular screw fixation technique: an anatomical feasibility and biomechanical study. J Neurosurg Spine 22:470477, 2015

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