Elsevier

World Neurosurgery

Volume 122, February 2019, Pages e1511-e1518
World Neurosurgery

Original Article
Clinical Outcomes of Atlantoaxial Dislocation Combined with High-Riding Vertebral Artery Using C2 Translaminar Screws

https://doi.org/10.1016/j.wneu.2018.11.092Get rights and content

Objective

Atlantoaxial stabilization procedures in high-riding vertebral artery (HRVA) cases are challenging. C2 translaminar screws are rigid and pose no risk to the vertebral artery. The aim of this study was to present clinical outcomes of atlantoaxial dislocation combined with HRVA using C2 translaminar screws.

Methods

Cases of atlantoaxial dislocation combined with HRVA surgically treated in our institution from 2007 to 2015 were retrospectively reviewed. Atlantodental interval and clivus-axial angle were measured. The Japanese Orthopaedic Association scale was used to evaluate neurologic status.

Results

There were 58 patients enrolled: 15 with instability and 43 with dislocation, 13 of which were irreducible. Incidence of bilateral HRVA was 5.2%. C1-C2 fixation was performed in 26 cases; atlantodental interval decreased from 9.9 ± 3.7 mm to 1.0 ± 1.7 mm (P < 0.05). C0-C2 fixation was performed in 32 cases; clivus-axial angle increased from 125° ± 13° to 150°± 15° (P < 0.05). Preoperative and postoperative Japanese Orthopaedic Association scores of 56 patients with myelopathy were 11.9 ± 2.8 and 14.6 ± 2.4, respectively (P < 0.05). Fusion rate was 93.1% (54/58) and at 4-month follow-up was 81% (47/58). In 14 cases of redislocation, final fusion was achieved; 3 of 14 required odontoidectomy. Four cases lacking bony fusion also required revision surgery. Redislocation rate was 31% (18/58), and reoperation rate was 12.1% (7/58).

Conclusions

Surgical results of C2 translaminar screws are unsatisfactory, with high redislocation and reoperation rates in atlantoaxial dislocation cases. New treatment methods should be investigated to facilitate clinical outcomes. Extending fixed segments should be considered.

Introduction

Multiple techniques have been used to stabilize the atlantoaxial joints. Posterior atlantoaxial transarticular screw fixation with wiring developed by Magerl can provide rigid internal fixation,1 and prior publications demonstrate a fusion rate up to 100%.2, 3 However, the Magerl technique is unsuitable for irreducible atlantoaxial dislocation (AAD)4 and causes vertebral artery (VA) injury in an estimated 4.1%–8.2% of cases.5, 6, 7 Goel et al.8 introduced the C1 lateral mass screw and C2 pedicle fixation, which was later popularized by Harms and Melcher.9 Some surgeons9 believe that this method can decrease the potential risk of VA injury, but anatomic studies indicated similar risks of VA injury between C2 pedicle screws and transarticular screws.10

In high-riding vertebral artery (HRVA), a common aberrant course of the VA, the transverse foramen of C2 is too medial and/or too high, which narrows the width of the C2 pedicle. The prevalence of HRVA is reportedly 18%–23%.6, 11, 12 Performing atlantoaxial stabilization procedures in HRVA cases is challenging; thus, spine surgeons developed various C2 screw fixation techniques to prevent VA injury, including short pedicle screws,13, 14, 15 pars/isthmus screws,4 translaminar screws (TLS),16, 17 new trajectory/unilateral transarticular screws,12, 18 and the hook-rod system.11 In this study, we used C2 TLS to treat patients with AAD combined with HRVA. To the best of our knowledge, this is the largest series to date.

Section snippets

Inclusion and Exclusion Criteria

This study was approved by our university hospital's ethics committee. We retrospectively reviewed our hospital electronic database from 2007 to 2015 and identified patients meeting the following criteria: presence of atlantoaxial instability or AAD; unilateral or bilateral HRVA detected on a sagittal image that was 3 mm lateral to the cortical margin of the spinal canal wall at C2, which was defined as an isthmus height ≤5 mm and/or an internal height ≤2 mm19; history of surgical treatment

Results

This study enrolled 58 patients (26 men, 32 women; mean age, 42.3 ± 14.3 years; range, 14–73 years). Preoperative diagnoses included instability in 15 patients and dislocation in 43 patients; of the latter, 13 were irreducible and required transoral release.20, 21 The incidence of bilateral HRVA was 5.2% (3 of 58 patients); thus, a total of 61 TLS were placed. C1-C2 fixation was performed in 26 patients without C1 occipitalization, 3 of whom underwent transoral release. Atlantodental interval

Discussion

The reported risk of VA injury in a clinical series was 4.1%–8.2%,5, 6, 7 which is predominant in cases combined with HRVA. Harms et al.9 recommended their technique as an efficient alternative to the Magerl technique with no vascular damage. Goel et al.8 also considered C2 pedicle screws to be able to decrease the risk of VA injury compared with the Magerl technique. However, Yoshida et al.10 judged approximately 10% of screw trajectories risky in both techniques, indicating the C2 pedicle

Conclusions

As an alternative option for C1-C2 or C0-C2 fixation, C2 TLS does not carry the risk of VA injury; however, the surgical results of TLS are unsatisfactory, and salvage surgery may be required. Thus, C2 TLS is unsuitable for AAD cases, and new treatment methods should be investigated to facilitate the clinical outcomes of AAD combined with HRVA. Perhaps extending fixed segments should be considered.

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      The presence of an HRVA, either unilateral or bilateral, will increase the risk of unsuccessful transarticular fixation and, at times, could completely preclude the safe insertion of the screws. If fusion is necessary in a patient with an HRVA, translaminar or spinous process bifid base screws could be applied on that side because they pose a much lower risk of injuring the vessel,6-8 although they do not have adequate potential for reduction maneuvers. Thus, preoperative awareness and early identification of the HRVA are essential for the choice of the fusion method and the outcome.

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    Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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