# Sagittal slope angle of lateral atlantoaxial articulation is associated with the severity of basilar invagination with atlantoaxial dislocation and predicts reduction degree after surgery

## TL;DR

This study shows that the angle of a specific joint in the neck is linked to the severity of a spinal condition and can predict how well surgery will correct it.

## Contribution

The sagittal slope angle of the lateral atlantoaxial articulation is identified as a novel predictor of surgical reduction outcomes in basilar invagination with atlantoaxial dislocation.

## Key findings

- Sagittal slope angle (SSA) was significantly smaller in patients with basilar invagination and atlantoaxial dislocation compared to controls.
- Minimum-SSA is an independent predictor of satisfactory post-surgical reduction with a cut-off value of -40.2.
- Dislocation severity correlates with SSA but not with coronal slope angle (CSA).

## Abstract

To investigate (1) lateral atlantoaxial articulation (LAA) morphology in patients with basilar invagination (BI) with atlantoaxial dislocation (AAD) and healthy individuals and its relationship with the severity of dislocation and (2) the effect of the LAA morphology on reduction degree (RD) after surgery.

In this retrospective propensity score matching case-control study, imaging and baseline data of 62 patients with BI and AAD from 2011 to 2022 were collected. Six hundred thirteen  participants without occipitocervical junctional deformity served as controls. Logistic regression and receiver operating characteristic (ROC) curve were used for analysis.

The age, BMI and sex did not differ significantly between the two groups after propensity score matching. Sagittal slope angle (SSA) and coronal slope angle (CSA) was lower and greater, respectively, in the patient group than in the control group. A negative SSA value usually indicates anteverted LAA. Regression analysis revealed a significant negative correlation between SSA and severity of dislocation. However, no relationship was found between CSA and the severity of dislocation. The multivariate logistic regression analysis revealed that minimum-SSA emerged as an independent predictor of satisfactory reduction (RD ≥ 90%). The ROC curve demonstrated an area under the curve of 0.844, with a cut-off value set at -40.2.

SSA in patients group was significantly smaller and more asymmetric than that in the control group. Dislocation severity was related to SSA but not to CSA. Minimum-SSA can be used as a predictor of horizontal RD after surgery.

The online version contains supplementary material available at 10.1186/s12891-024-07696-4.