The Cricothyroid Joint: A Practical Guide for Distinguishing Between Different Joint Types.

OBJECTIVE: Type A cricothyroid joint (CTJ) leads to a higher elongation of the vocal folds than Type B/C CTJ. Therefore, the determination for the CTJ type is important whether to perform a cricoid-thyroid approximation for a pitch elevation in transwomen with gender dysphoria. This study aimed to develop a tool for clinicians and radiologists for distinguishing between Type A (cricoid cartilage protuberance) and Type B/C (flat surface with/without cartilage of the cricoid) CTJs on high-resolution computed tomography (HRCT).

STUDY DESIGN: This was a prospective study.

METHODS: Analysis of 60 male HRCTs and 60 female HRCTs of the larynx/CTJs. Three-dimensional reconstruction of the laryngeal cartilages, based on visualization of the CTJ in HRCT scans. The intercartilaginous distances (nearest distance between the inner side of the Thyroid and outer side of the cricoid of the CTJ) were measured to compare different types of CTJs.

RESULTS: In all HRCT scans, three-dimensional reconstructions of the CTJ were feasible. All Type A CTJs showed the typical cricoid cartilage protuberance (like a volcano) in biplanar images and three-dimensional reconstructions. All Type B/C CTJs showed a flat cricoid joint cartilage in biplanar images and three-dimensional reconstructions. The type distribution was Type A: 61% in male and female larynges; Type B/C: 39% in male and female larynges. The intercartilaginous distances were Type A: 0.71mm [0.42-0.98] in male larynges and 0.75mm [0.44-1.40] in female larynges; Type B/C: 1.13mm [0.36-1.24] in male larynges and 1.32mm [0.76-2.47] in female larynges.

CONCLUSIONS: In HRCT scans, the Type A CTJ showed an intercartilaginous space less than 1mm. In contrast, the Type B/C CTJ showed an intercartilaginous distance exceeded 1mm.