Defining the role of the condylar–C2 sagittal vertical alignment in Chiari malformation type I

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  • 1 Division of Pediatric Neurosurgery, Department of Neurosurgery, University of Utah, Salt Lake City, Utah; and
  • 2 Department of Surgery, Texas Children’s Hospital, Houston, Texas
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OBJECTIVE

The authors’ objective was to better understand the anatomical load-bearing relationship between the atlantooccipital joint and the upper cervical spine and its influence on the clinical behavior of patients with Chiari malformation type I (CM-I) and craniocervical pathology.

METHODS

In a single-center prospective study of patients younger than 18 years with CM-I from 2015 through 2017 (mean age 9.91 years), the authors measured the occipital condyle–C2 sagittal vertebral alignment (C–C2SVA; defined as the position of a plumb line from the midpoint of the occiput (C0)–C1 joint relative to the posterior aspect of the C2–3 disc space), the pB–C2 (a line perpendicular to a line from the basion to the posteroinferior aspect of the C2 body on sagittal MRI), and the CXA (clivoaxial angle). Control data from 30 patients without CM-I (mean age 8.97 years) were used for comparison. The primary outcome was the need for anterior odontoid resection and/or occipitocervical fusion with or without odontoid reduction. The secondary outcome was the need for two or more Chiari-related operations.

RESULTS

Of the 60 consecutive patients with CM-I identified, 7 underwent anterior odontoid resection or occipitocervical fusion and 10 underwent ≥ 2 decompressive procedures. The mean C–C2SVA was greater in the overall CM-I group versus controls (3.68 vs 0.13 mm, p < 0.0001), as was the pB–C2 (7.7 vs 6.4 mm, p = 0.0092); the CXA was smaller (136° vs 148°, p < 0.0001). A C–C2SVA ≥ 5 mm was found in 35% of CM-I children and 3.3% of controls (p = 0.0006). The sensitivities and specificities for requiring ventral decompression/occipitocervical fusion were 100% and 74%, respectively, for C–C2SVA ≥ 5 mm; 71% and 94%, respectively, for CXA < 125°; and 71% and 75%, respectively, for pB–C2 ≥ 9 mm. The sensitivities and specificities for the need for ≥ 2 decompressive procedures were 60% and 70%, respectively, for C–C2SVA ≥ 5 mm; 50% and 94%, respectively, for CXA < 125°; and 60% and 76%, respectively, for pB–C2 ≥ 9 mm. The log-rank test demonstrated significant differences between C–C2SVA groups (p = 0.0007) for the primary outcome. A kappa value of 0.73 for C–C2SVA between raters indicated substantial agreement.

CONCLUSIONS

A novel screening measurement for craniocervical bony relationships, the C–C2SVA, is described. A significant difference in C–C2SVA between CM-I patients and controls was found. A C–C2SVA ≥ 5 mm is highly predictive of the need for occipitocervical fusion/ventral decompression in patients with CM-I. Further validation of this screening measurement is needed.

ABBREVIATIONS C–C2SVA = occipital condyle–C2 SVA; CCJ = craniocervical junction; CM = Chiari malformation; CM-I = CM type I; CXA = clivoaxial angle; C0 = occiput; OI = occipital incidence; OS = occipital slope; OT = occipital tilt; pB–C2 = a line perpendicular to a line from the basion to the posteroinferior aspect of the C2 body on sagittal MRI; PI = pelvic incidence; SVA = sagittal vertical alignment.

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Contributor Notes

Correspondence Douglas L. Brockmeyer: Primary Children’s Hospital, Salt Lake City, UT. neuropub@hsc.utah.edu.

INCLUDE WHEN CITING Published online July 17, 2020; DOI: 10.3171/2020.4.PEDS20113.

V.M.R. and R.R.I. contributed equally to this work.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

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