The Effects of Thyroplasty Implant Shape and Stiffness on Voice Acoustics and Perception

Introduction: Treatment for glottic insufficiency includes Type I thyroplasty in which an implant is inserted into the paraglottic space to medialize the vocal folds. Although a variety of implant shapes, sizes and materials are used, there is no consensus on optimal implant features. This study evaluates the effects of implant shape and stiffness on voice acoustics and perception.

Methods: Thyroplasty implants of varying medial surface shapes (rectangular, convergent, and divergent) and stiffnesses (Silastic, Gore-tex, hydrogel, and silicone) were tested in an in vivo canine model of phonation. Acoustic quality of each phonatory condition was assessed by measuring cepstral peak prominence (CPP), harmonic amplitude (H1-H2), and root-mean-square (RMS) energy. A perceptual analysis was performed on listener responses in a visual sort-and-rate task. The relationships between implant features (shape and stiffness), acoustic metrics, and perceptual ratings were evaluated.

Results: Rectangular medial surface shape and silastic stiffness implants consistently demonstrate improved voice quality as measured by CPP. Furthermore, CPP is the only acoustic metric that is positively correlated with listener preference across all experiments (p < 0.001). Silicone of moderate stiffness is most preferred across experiments while no consistent relationship between perceptual pattern of preference and a medial surface shape is observed.

Conclusions: Rectangular silastic implants produced the greatest improvement in voice quality. These findings further our knowledge in the optimization of thyroplasty implants in the treatment of glottic insufficiency.