# Proposal of Hard Palate-C2-Hyoid Bone Angle as a New Parameter Possibly Related to Dysphagia as a Postoperative Complication of Upper Cervical Fixation: A Case Series and Pilot Study

## TL;DR

This study introduces a new radiological parameter, the H2H angle, which may help predict dysphagia after upper cervical spine surgery.

## Contribution

The study proposes the hard palate-C2-hyoid bone angle as a novel parameter for predicting postoperative dysphagia.

## Key findings

- Dysphagia occurred in two patients after OCF surgery.
- Changes in the H2H angle were plotted as outliers in cases with dysphagia.
- Other radiological parameters did not show significant changes in dysphagia cases.

## Abstract

Introduction: Occipitocervical fusion (OCF) and upper cervical posterior fixation can be performed to resolve occipitocervical or upper cervical instability. The cervical vertebral realignment following these procedures can result in dysphagia, which can decline patients’ postoperative status. Several radiological parameters on cervical lateral X-ray images were proposed to predict and avoid this postoperative dysphagia. However, previous parameters principally focus on cervical alignment and do not include the hyoid bone, which is an essential anatomical structure related to the swallowing mechanism.

Methods: In this case-series study, we enrolled a total of 14 patients (male: female = 10:4) with a mean age of 66.4 years who underwent OCF or upper cervical posterior fixation. We measured the following parameters on cervical lateral X-ray images: T1 slope, pharyngeal airway space, and O-C2, C1-C2, C2-C7, and pharyngeal tilt angles. In addition to these parameters, we also defined and measured a hard palate-C2-hyoid bone (H2H) angle, which reflects the anatomical relationship among the cervical vertebrae, palate, and hyoid bone. We compared pre- and postoperative changes of all the parameters between those patients with postoperative dysphagia after OCF and upper cervical posterior fixation and those without.

Results: Dysphagia occurred in two cases treated with OCF. A chronological change of the H2H angle in a case with postoperative dysphagia was plotted as an outlier on box-and-whisker plots, while any chronological changes of the other parameters in cases with dysphagia were not plotted as outliers.

Conclusion: The H2H angle could be related to the occurrence of postoperative dysphagia after OCF and upper cervical posterior fixation. This parameter should be evaluated with further studies.