A multicenter validation of the condylar-C2 sagittal vertical alignment in Chiari malformation type I: a study using the Park-Reeves Syringomyelia Research Consortium

OBJECTIVE

The condylar-C2 sagittal vertical alignment (C-C2SVA) describes the relationship between the occipitoatlantal joint and C2 in patients with Chiari malformation type I (CM-I). It has been suggested that a C-C2SVA ≥ 5 mm is predictive of the need for occipitocervical fusion (OCF) or ventral brainstem decompression (VBD). The authors' objective was to validate the predictive utility of the C-C2SVA by using a large, multicenter cohort of patients.

METHODS

This validation study used a cohort of patients derived from the Park-Reeves Syringomyelia Research Consortium; patients < 21 years old with CM-I and syringomyelia treated from June 2011 to May 2016 were identified. The primary outcome was the need for OCF and/or VBD. After patients who required OCF and/or VBD were identified, 10 age- and sex-matched controls served as comparisons for each OCF/VBD patient. The C-C2SVA (defined as the position of a plumb line from the midpoint of the O-C1 joint relative to the posterior aspect of the C2-3 disc space), pBC2 (a line perpendicular to a line from the basion to the posteroinferior aspect of the C2 body), and clival-axial angle (CXA) were measured on sagittal MRI. The secondary outcome was the need for ≥ 2 CM-related operations.

RESULTS

Of the 206 patients identified, 20 underwent OCF/VBD and 14 underwent repeat posterior fossa decompression. A C-C2SVA ≥ 5 mm was 100% sensitive and 86% specific for requiring OCF/VBD, with a 12.6% misclassification rate, whereas CXA < 125° was 55% sensitive and 99% specific, and pBC2 ≥ 9 was 20% sensitive and 88% specific. Kaplan-Meier analysis demonstrated that there was a significantly shorter time to second decompression in children with C-C2SVA ≥ 5 mm (p = 0.0039). The mean C-C2SVA was greater (6.13 ± 1.28 vs 3.13 ± 1.95 mm, p < 0.0001), CXA was lower (126° ± 15.4° vs 145° ± 10.7°, p < 0.05), and pBC2 was similar (7.65 ± 1.79 vs 7.02 ± 1.26 mm, p = 0.31) among those who underwent OCF/VBD versus decompression only. The intraclass correlation coefficient for the continuous measurement of C-C2SVA was 0.52; the kappa value was 0.47 for the binary categorization of C-C2SVA ≥ 5 mm.

CONCLUSIONS

These results validated the C-C2SVA using a large, multicenter, external cohort with 100% sensitivity, 86% specificity, and a 12.6% misclassification rate. A C-C2SVA ≥ 5 mm is highly predictive of the need for OCF/VBD in patients with CM-I. The authors recommend that this measurement be considered among the tools to identify the "high-risk" CM-I phenotype.

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

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.

Relationship of Cervical Sagittal Vertical Alignment After Sagittal Balance Correction in Adult Spinal Deformity: A Retrospective Radiographic Study

Study Design

Retrospective radiographic study.

Purpose

Predict the variability of the center of gravity of head (COG) relative to the global cervical sagittal alignment (SVA).

Background

Cervical lordosis, thoracic kyphosis, lumbar lordosis, and pelvic incidence are considered interrelated, with changes in SVA causing reciprocal changes to bring the head over pelvis. The implications of cervical deformities have generated more interest recently, and it has been shown that poor cervical alignment is associated with poor clinical outcomes.

Methods

Patients were selected from the imaging server of a single institution with adult spinal deformity (ASD) and SVA, who underwent surgical correction from 2008 to 2013. Three observers performed the measurements, and intraclass correlation coefficient (ICC) was measured for inter and intraobserver reliability. Group 1 was patients with unbalanced spines (C7-SVA > 5 cm) preoperatively and corrected to full balanced spine (C7-SVA < 5 cm) until last follow-up. Group 2 was improved in sagittal balance after surgery and maintained SVA correction until last follow-up, but not fully balanced.

Results

Fifty-five patients met the inclusion criteria, 42 patients improved in SVA after surgery, and 13 showed no improvement. Twenty-three patients kept full balanced measurements until last follow-up, and 19 patients maintained not-full balanced spine. In group 1, there was no change in pre and postoperative parameters except for C2-CL (21.74° vs 16.91°, P = .033). It was similar in group 2, no differences except for C2-CL (21.67° vs 17.81°, P = .018).

Conclusion

Parameters in this study failed to yield predictable relationships when compared to changes in SVA. The position of COG may be independent of global SVA.

Clinical Relevance

This study aims to improve our understanding of the dynamic changes and relationships of the regional and global spinal parameters with regard to spinal deformity corrective surgeries in adults.

Level of Evidence

III.

Comparison of structural allograft and traditional autograft technique in occipitocervical fusion: radiological and clinical outcomes from a single institution

OBJECT The authors' objectives were to compare the rate of fusion after occipitoatlantoaxial arthrodesis using structural allograft with the fusion rate from using autograft, to evaluate correction of radiographic parameters, and to describe symptom relief with each graft technique. METHODS The authors assessed radiological fusion at 6 and 12 months after surgery and obtained radiographic measurements of C1-2 and C2-7 lordotic angles, C2-7 sagittal vertical alignments, and posterior occipitocervical angles at preoperative, postoperative, and final follow-up examinations. Demographic data, intraoperative details, adverse events, and functional outcomes were collected from hospitalization records. Radiological fusion was defined as the presence of bone trabeculation and no movement between the graft and the occiput or C-2 on routine flexion-extension cervical radiographs. Radiographic measurements were obtained from lateral standing radiographs with patients in the neutral position. RESULTS At the University of Utah, 28 adult patients underwent occipitoatlantoaxial arthrodesis between 2003 and 2010 using bicortical allograft, and 11 patients were treated using iliac crest autograft. Mean follow-up for all patients was 20 months (range 1-108 months). Of the 27 patients with a minimum of 12 months of follow-up, 18 (95%) of 19 in the allograft group and 8 (100%) of 8 in the autograft group demonstrated evidence of bony fusion shown by imaging. Patients in both groups demonstrated minimal deterioration of sagittal vertical alignment at final follow-up. Operative times were comparable, but patients undergoing occipitocervical fusion with autograft demonstrated greater blood loss (316 ml vs 195 ml). One (9%) of 11 patients suffered a significant complication related to autograft harvesting. CONCLUSIONS The use of allograft in occipitocervical fusion allows a high rate of successful arthrodesis yet avoids the potentially significant morbidity and pain associated with autograft harvesting. The safety and effectiveness profile is comparable with previously published rates for posterior C1-2 fusion using allograft.