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. 2025 Jun 2;24(4):107.
doi: 10.1007/s12311-025-01865-4.

A Novel Metric for Assessing Long-Term Outcomes in Adults with Chiari Malformation Type I: Occipitocervical Dura Angulation (ODA)-Applications and Value

Bo Wang #  1   2 , Shi-Chao Chen #  1   2   3 , Yao-Wu Zhang  1   2 , Wei-Hao Liu  1   2 , Chong Wang  1   2 , Yi-Xiang Liu  1   2 , Guang-Hao Zheng  1   2 , Jia-Lin Li  1   2   4 , Kai Ji  1   2 , Jun Yang  1   2 , Yong-Zhi Wang  5   6   7 , Wen-Qing Jia  8   9   10
Affiliations

A Novel Metric for Assessing Long-Term Outcomes in Adults with Chiari Malformation Type I: Occipitocervical Dura Angulation (ODA)-Applications and Value

Bo Wang et al. Cerebellum. .

Abstract

Foramen magnum decompression with duraplasty (FMDD), a common surgery for adult Chiari malformation type I(CM-I) with a 60-70% improvement rate, lacks assessment metrics. This study applied the concept of occipitocervical dura angulation (ODA) and aimed to investigate ODA's role in evaluating long-term FMDD outcomes. The ODA normal range was measured in 230 healthy individuals. We included 160 CM-I adults who underwent FMDD over 10 years. Long-term outcomes (> 1 year) were evaluated using the Chicago Chiari Outcome Scale(CCOS). The cohort was grouped to analyze ODA's role in assessing and predicting FMDD outcomes. The normal range of ODA was 104°-145°, with an average value of 124.2 ± 10.4°. The median patient age was 46 years (range: 18-64 years). The median follow-up period was 64.5 months (range: 18-123 months). The cohort was divided into two groups based on preoperative ODA: group A (n = 90) with ODA < 125° and group B (n = 70) with ODA ≥ 125°. Group B had a significantly better prognosis than that of group A (P = 0.012). Logistic regression analysis revealed that an increase in ODA was associated with clinical outcomes in both groups. The receiver operating characteristic curve showed that ODA increases of > 10° and > 3° could be considered as credible threshold values for groups A and B, respectively. ODA is a reliable predictor of prognosis. FMDD should result in an increased ODA, which is one of the criteria for surgical validity, especially for those with a preoperative ODA of < 125°.

Keywords: Chiari malformation type I; Long-term Outcomes; Occipitocervical dura angulation.

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Conflict of interest statement

Declarations. Ethical Approval: This retrospective study followed the principles of the Declaration of Helsinki. This study was approved by institutional review boards of Beijng Tiantan Hospital, Capital Medical University. Consent to Participate: Informed consent was obtained from all individual participants included in the study. Competing Interests: The authors declare no competing interests.

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