Three‐Dimensional Conformation of the Injected Bolus in Vocal Fold Injections in a Cadaver Model

Abstract

Objective To determine the 3-dimensional (3D) conformation of the injected bolus in the larynx in vocal fold injections, to understand how the bolus interacts spatially with elements of the laryngeal framework, and to relate the above to clinical observations in performing vocal fold injections. Study Design Excised cadaveric larynx study. Setting Laboratory. Subjects and Methods Vocal folds of 12 human excised cadaveric larynges were injected with calcium hydroxylapatite. High-resolution computed tomography scans were obtained of the injected larynges. Densities corresponding to the injected bolus and the laryngeal framework were extracted and processed with MATLAB routines to generate selective 3D reconstructions of the injected bolus within the laryngeal framework. Histology analysis was also performed to correlate with observations from the 3D reconstructions. Results Boluses injected into the lateral aspect of the thyro-arytenoid muscle tended to be irregularly shaped, appeared to fill up the paraglottic space, and were associated with significant muscle compression. The vertical thickness of the injected boluses averaged 9.5 mm for lateral boluses and 7.6 mm for medial boluses, which were comparable to the vertical thickness of uninjected vocal folds. Conclusion Laterally injected boluses are shaped by spatial constraints imposed by elements of the laryngeal framework. Compression of vocal fold muscle may be a mechanism accounting for stiffness from overinjection. The irregular shapes of some boluses may affect the outcome of subsequent medialization attempts. Injections may enhance the vocal fold contact height as a favorable effect beyond simple medialization.

Modulating phonation through alteration of vocal fold medial surface contour

“…5). The volume used (median, 0.0625 mL) was substantially less than what is required to medialize a vocal fold through a medial injection (0.14–0.23 mL) 24. Despite this effort, it is possible that some degree of prephonatory glottal area reduction might have accompanied the medial surface contour change, so that the effect due to the change in the vertical dimension could not be assessed independently from that due to the change in the transverse dimension, that is, glottal area.…”

“…Lateral injection was deliberately not used for this purpose because laterally injected boluses have been shown to adopt irregular shapes in the paraglottic space 23. Medially injected boluses, in contrast, tend to be more geometrically uniform, possibly due to their smaller volumes and proximity to the vocal ligament, which acts as a geometric constraint 23, 24. Medial injection was therefore used in this study for the experimental purpose of altering vocal fold medial surface contour with relative reproducibility.…”

“…2). 24 The next logical step is to investigate whether such alterations, for example, the change of a convergent glottal geometry to a more rectangular or less convergent one, as conceptualized in Figure 3, would in fact lead to functional gain, as predicted by biomechanical models of phonation 15, 17…”

“…(C) Superimposition of the postinjection contour onto the preinjection image. Previously unpublished data from work described in Mau and Courey 23…”

Combining Multiobjective Optimization and Cluster Analysis to Study Vocal Fold Functional Morphology

“…In contrast, the problem investigated here was to better understand the relationship between the decision space and the objective space. The larynx as a vocal organ can naturally produce a large range of sounds, yet there are specializations facilitating species-specific vocal behavior [35], and there is large interest in predicting what small changes to the integrity of the vocal folds will do to the voice of a person [38], [39]. The cluster analysis helps to relate morphological to acoustic spaces.…”