Atlantal facet geometry in Chiari I malformation

Chiari I malformation (CMI) is a complex condition characterized by cerebellar herniation through the foramen magnum and is frequently coincident with other craniovertebral junction abnormalities. Symptoms are varied, and the complete disease etiology is poorly understood. The primary aim of our study is to assess atlantal facet geometry in CMI patients to further elucidate disease pathogenesis.

Forty-six CMI-affected female patients (29.48 years ± 8.35) (Chiari1000 database) and 55 female controls (32.11 years ± 4.81) (New Mexico Decedent Image Database [NMDID]) were included. Twenty 3D landmarks were placed around the perimeter of each facet by a blinded landmarker. Coordinates were subjected to a generalized Procrustes superimposition. A between-groups principal component analysis (bgPCA) was used to explore differences between groups. The protocol was completed by a second landmarker to validate results.

The bgPCA scores were significantly different between CMI patients and controls (W = 689, P = 0.00022). Chiari malformation patients tended to have more negative overall scores, which coincided with smaller, more horizontally oriented facets. These differences were driven largely by the anterior aspect of the facets, which in CMI patients were notably blunted, lacking the typical medial angulation that contributes to the facet's usually reniform shape. The error study conducted by the second blinded landmarker yielded similar differences between CMI and control groups (W = 704, P = 0.00104).

The geometric analysis suggests distinct facet differences in CMI facet shape. CMI etiology is complex, and wholistic anatomical assessment using geometric or multiplanar methods may identify new clinical targets or provide a fresh approach to morphologically driven pathogenesis.