The role of the cricothyroid joint anatomy in cricothyroid approximation surgery

Cricothyroid approximation (CTA) surgery aims at raising the voice pitch in male-to-female transsexuals. However, 30% of the patients are not satisfied with the result. The purpose of our study was to examine the cricothyroid joint (CTJ) biomechanics and to analyze if (and how) the CTJ anatomy influences the movement of the cricoid and, consequently, the elongation of the vocal fold and the voice pitch after CTA.

Twenty-four cadaver larynges were examined with high-resolution computerized tomography and MIMICS three-dimensional imaging software (Materialise Interactive Medical Image Control System, Leuven, Belgium). After superimposing the two scans taken in "neutral" and in "CTA" positions, vector geometrical analysis was used to determine the effective rotation axis of the CTJ and to calculate the elongation of the vocal folds after CTA.

Our results showed that the cricoid rotates around an axis, the position of which depends on the anatomical structure of the CTJ. Based on the location of this effective rotation axis, we could distinguish three groups. In group I (N=13), the rotation axis was located in the lower third; in group II (N=5), it was located in the middle third; and in group III (N=6), it was located in the upper third of the cricoid. The elongations of the vocal fold were 12%, 8%, and 3%, in groups I, II, and III, respectively.

The anatomical structure of the CTJ influences directly (1) the position of the effective rotation axis and (2) the elongation of the vocal folds.