Virginia Research Day 2025

Medical Student Research Biomedical

06 Skeletal Deformities in Chiari I Malformation Extend into the Cervical Spine: Considering Facet Morphology as a Driver of Symptoms in Chiari-Affected Patients

Brooke Scardina; Blake Rondon; Ishan Perera; Cara Satoskar; Jonathan Millard Corresponding author: bscardina@vcom.edu

Edward Via College of Osteopathic Medicine - Virginia Campus

Chiari I Malformation (CMI) is traditionally diagnosed radiologically as caudal descent of the cerebellar tonsils through the foramen magnum. Despite being a common radiologic diagnosis, many patients with CMI diagnosis never develop symptoms, and the mechanisms driving symptomatology are poorly understood. While most research attention has been focused on occipital bone hypoplasia, recent investigations have linked CMI with craniocervical instability, and many patients who undergo decompression surgery only experience relief after subsequently undergoing occipitocervical fusion. Theoretically, this fusion prevents excessive motion between the skull and atlas bone, which discourages the abnormal cerebrospinal fluid (CSF) circulation patterns thought to worsen symptoms. Intrinsically unstable joints may allow turbulent CSF flow and therefore may be a driver of these symptoms. Our objective is to describe the shape of the superior articular facet of the atlas using geometric morphometric techniques and test the hypothesis that the superior articular facet is shaped differently between patients with Chiari I malformation (CMI)

and age/sex-matched controls. Atlas bones from 30 symptomatic CMI patients and 32 age and sex matched controls were manually segmented from computed tomography scans. A researcher blinded to group identities used the markups module in 3DSlicer (v 5.6.2) to place 20 bilateral, equidistant semilandmarks around the perimeter of the superior articular surface of the lateral mass. The slicermorph module was used to apply a generalized Procrustes superimposition and principal component analysis (PCA) to assess shape variation in the sample. A Mann-Whitney U Test was applied to the resulting principal component (PC) scores to evaluate differences between groups. To assess the protocol’s reliability, a second blinded researcher re-landmarked the sample and the results were compared. The PCA resulted in 62 PCs with the first PC accounting for 24.7% of the variability in the sample. The PC1 shape axis was characterized by changes in facet depth and angle, with more negative scores being associated with deeper, elongated, and obliquely angled surfaces. Positive scores along PC1 were associated with more

shallow, circular, and horizontally angled surfaces. Scores were significantly different between groups ( U = 319, p = 0.023), with CMI patients clustered toward the negative end of the axis. Results of the blinded error study replicated findings along the PC1 axis ( U = 308, p = 0.016), engendering confidence in the results. These results suggest that there are distinct bony differences in the superior articular facets of CMI patients. Specifically, CMI facets are shallower and more horizontally oriented. This morphology may allow excess gliding between the bones and contribute to instability at the atlanto-occipital joint, thereby exacerbating symptoms. These results provide a mechanistic explanation for the clinical outcomes seen in patients who fail to get relief from decompression surgeries but are subsequently relieved by occipitocervical fusion. This also suggests that cervical stabilization should be heavily considered in surgical cases, instead of decompression alone. This protocol was reviewed and approved by the VCOM IRB (#2024-195).

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2025 Research Recognition Day