We present a novel implant for type I thyroplasty which offers customizability according to patient anatomy as well as postoperative adjustability. Even at this preliminary prototypical stage, the implant provided effective medialization which improved vocal performance.
Glottal gap was decreased upon insertion of the ABI, placing the paralyzed vocal fold in a position more conducive for voicing and increasing phonatory efficiency. PTP, PTF, and PTW were all significantly decreased, though not to the levels observed for the normal condition. This can likely be attributed to a slight posterior glottal gap caused by the round shape of the implant. Such a posterior glottal chink could be corrected with an arytenoid adduction. Evaluating the effect of combined arytenoid adduction with ABI thyroplasty will be the subject of future study.
The ABI not only improved the acoustic parameters of interest, but also restored SNR, percent jitter, and percent shimmer to normal or near normal levels. While it did increase F0, the resultant frequency was discernibly, though not significantly, less than normal. Improvement of perturbation parameters to approximately normal levels can be attributed to restoration of vocal fold contact and vibrational periodicity. Increased SNR occurred due to decreased airflow required for phonation as well as increased acoustic output.
Interestingly, insignificant increases in the mucosal wave amplitude of the right and left vocal folds were observed from the normal to paralyzed condition. Based on experimental observations, this appeared to be due to the high airflow through the glottis required for phonation. However, without vocal fold contact, vocal quality was poor despite the large amplitude. Insertion of the ABI closed the glottal gap and preserved mucosal wave amplitude, resulting in improved vocal quality. Following insertion of the ABI, the mucosal wave was preserved.
There are several limitations to the experimental design and implant which will be the subject of future investigations. While the excised larynx setup is a valuable research tool and has been used frequently to study VFP,5,16,17,19,20
it cannot simulate all clinical concerns of thyroplasty such as physiological tissue response to implant insertion and long-term effectiveness of the implant. Second, a round balloon was used in this study which has the natural tendency to expand uniformly in all directions. This was mitigated by the use of the aluminum frame, which compressed the balloon superiorly and inferiorly, ensuring that the primary force of the balloon on the vocal fold was directed medially. Third, though silicone is a widely used in medical applications including thyroplasty, allergic reaction has been reported.21
Covering the implant with a biointegratable material such as Gore-Tex could address this concern, preserving the advantages of the ABI while eliminating the possibility of an adverse reaction. Continued use of the excised larynx setup will allow us to evaluate implant modifications objectively and quickly before they are applied to human patients.
Application of the ABI to human patients would require several steps not required for this preliminary excised larynx experiment. After insertion of the implant, two to three centimeters of tubing would be left protruding from the balloon to allow for postoperative adjustments to implant volume. The tubing would be sealed with surgical glue prior to closure of the surgical site. Tubing could be left external to the skin similar to a wound drainage tube or, alternatively, left along the inferior margin of the thyroid cartilage. A minor incision at the anteroinferior aspect of the thyroid cartilage would allow for access to the tubing, while blue prolene suture attached to the most distal aspect of the tubing could facilitate visualization. Initial closure of the implant tubing is accomplished with a one-way valve and distal occlusion of the tube lumen with surgical glue. Adjusting the volume can be accomplished by severing the tubing proximal to the seal, increasing or decreasing the amount of saline injected, and then re-occluding the lumen with surgical glue.
To increase procedural effectiveness and the simplicity of ABI insertion, implant and methodological modifications will be evaluated. The spherical balloon shape used in this study is the primary limitation of the ABI. Using a wedge-shaped balloon instead could close the posterior glottal chink as well as prevent overadduction at the anterior commissure. This could also eliminate the need for the supporting frame, opening up the possibility for implant insertion via an anterior microthyrotomy approach. Standard landmarks used in traditional thyroplasty such as the inferior margin of the thyroid cartilage and the anterior commissure could be used to ensure proper vertical placement is maintained. Such an approach would not require the traditional large neck incision currently used for thyroplasty and may also prevent cracking of the thyroid cartilage, particularly in elderly patients, that can occur when making a thyroplasty window. This procedure would be easily reversible, as only a small hole in the anterior thyroid lamina would be needed for implant insertion.
While these modifications could be valuable as the ABI is improved, it is important to note the advantages of the ABI even at this early stage. One implant was used for all larynges in this study, which included specimens of varying size, and provided adequate medialization in all cases. The ABI was easy to insert and required no pre- or intraoperative modifications, such as carving with a Silastic implant. It was easy to adjust medialization incrementally and determine the optimal degree of medialization for a superior vocal outcome (). If excess saline was injected and pressed phonation resulted, the excess could easily be removed until optimal vocal quality returned. As modifications to the ABI are made, these benefits will be preserved.
Figure 9 Incremental adjustments to the volume of saline injected into the implant. A) larynx with simulated right vocal fold paralysis; B) larynx with the implant inserted but no saline injected; C) 0.4 cc injected; D) 0.6 cc injected; E) 1.0 cc injected; F) (more ...)