Thyroid cartilage loci and hyoid bone analysis using a video fluoroscopic swallowing study (VFSS) Introduction: Hyoid bone movement can be useful for diagnosing oropharyngeal dysphagia. In most clinical settings, the movement can be evaluated by a video fluoroscopic swallowing study (VFSS) that induces radiation exposure. In contrast with the hyoid bone, the thyroid cartilage is easily seen through the anterior neck surface. We hypothesized that the movement of thyroid cartilage correlates with hyoid bone movement in various axis and can be used as a parameter to evaluate swallowing. The purpose of this study was to investigate whether thyroid cartilage and hyoid bone movement were correlated and to collect basic data to determine if thyroid cartilage can be used as a parameter to evaluate swallowing. Methods: A total of 25 subjects were included, and the VFSS image with normal swallowing function was collected retrospectively. The VFSS image was analyzed by specially developed semi-automatic software. Laryngeal prominence and anterior-superior margins of the hyoid were automatically extracted during swallowing. Two-point sets of the loci during swallowing were obtained in all VFSS frames. The X-coordinates showed an anterior-posterior axis, and the Y-coordinates showed a superior-inferior axis. Pearson correlation coefficients for each X- and Y-coordinate component were computed. Results: X- and Y-coordinates of the thyroid cartilage and hyoid bones in all subjects showed movement in similar patterns, although each subject's movement differed. Pearson correlation coefficients of X- and Y-coordinate components of all subjects ranged from 0.611 to 0.981, which indicated that thyroid cartilage and hyoid bone movement was strongly correlated in anterior-posterior and superior-inferior axes, respectively. Conclusion: We analyzed thyroid cartilage and hyoid bone movement using a specifically developed semi-automatic software and concluded that the movement of thyroid cartilage and hyoid bone was strongly correlated in anterior-posterior and superior-inferior axes, respectively, during swallowing. The present study implies that analysis of thyroid cartilage movement can be used as a parameter for swallowing evaluation.