UCLA

Objectives

Vocal fold (VF) stiffness and geometry are determinant variables in voice production. Type 1 medialization thyroplasty (MT), the primary surgical treatment for glottic insufficiency, changes both of these variables. Understanding the cause and effect relationship between these variables and acoustic output might improve voice outcomes after MT. In this study, the effects of thyroplasty implants with variable stiffness on glottal shape and acoustics were investigated.

Methods

In an ex vivo human larynx phonation model, bilateral MT with implants of four stiffness levels (1386, 21.6, 9.3, and 5.5 kPa) were performed. Resulting acoustics and aerodynamics were measured across multiple airflow levels. A vertical partial hemilaryngectomy was performed and stereoscopic images of the VF medial surface taken to reconstruct its three-dimensional (3D) surface contour. The results were compared across implants.

Results

The effects of implant stiffness on acoustics varied by airflow. Softer implants resulted in improved acoustics, as measured by cepstral peak prominence (CPP), at lower airflow levels compared to stiffer implants but this relationship reversed at high airflow levels. Stiffer implants generally required less airflow to generate a given subglottal pressure. Stiffer implants resulted in greater medialized surface area and maximal medialization, but all implants had similar effects on overall VF medial surface contour.

Conclusion

Softer implants result in less medialization but better acoustics at low airflow rates. Stiffer implants provide better acoustics and more stable pressure-flow relationships at higher airflow rates. This highlights a potential role for patient-specific customized thyroplasty implants of various stiffness levels.

Level of evidence

NA.