Cross-linked hyaluronan used as augmentation substance for treatment of glottal insufficiency: safety aspects and vocal fold function

Injection laryngoplasty

After a nearly a century of development, augmentation of laryngeal tissue through injection remains as complex a procedure as it was in the earlier part of the century. Initially, the number of surgeons performing injection laryngoplasty was limited since the technique of injection was thought to be difficult and the selection of cases was thought to require the judgment of an accomplished laryngologist. Performing successful injection laryngoplasty does in fact require an understanding of laryngeal anatomy and physiology, and the physical characteristics of the substance to be injected. In addition, the surgeon must be aware of potential host reactions to the injected material. Finally, the surgeon must have an understanding of the etiology and configuration of the glottic insufficiency, and keep in mind the goals of the procedure.

Viscoelasticity of Rabbit Vocal Folds After Injection Augmentation

OBJECTIVES/HYPOTHESIS

Vocal fold function is related to the viscoelasticity of the vocal fold tissue. Augmentation substances used for injection treatment of voice insufficiency may alter the viscoelastic properties of vocal folds and their vibratory capacity. The objective was to compare the mechanical properties (viscoelasticity) of various injectable substances and the viscoelasticity of rabbit vocal folds, 6 months after injection with one of these substances.

STUDY DESIGN

Animal model.

METHODS

Cross-linked collagen (Zyplast), double cross-linked hyaluronan (hylan B gel), dextranomers in hyaluronan (DHIA), and polytetrafluoroethylene (Teflon) were injected into rabbit vocal folds. Six months after the injection, the animals were killed and the right- and left-side vocal folds were removed. Dynamic viscosity of the injected substances and the vocal folds was measured with a Bohlin parallel-plate rheometer during small-amplitude oscillation.

RESULTS

All injected vocal folds showed a decreasing dynamic viscosity with increasing frequency. Hylan B gel and DiHA showed the lowest dynamic viscosity values, and vocal folds injected with these substances also showed the lowest dynamic viscosity (similar to noninjected control samples). Teflon (and vocal folds injected with Teflon) showed the highest dynamic viscosity values, followed by the collagen samples.

CONCLUSION

Substances with low viscoelasticity alter the mechanical properties of the vocal fold to a lesser degree than substances with a high viscoelasticity. The data indicated that hylan B gel and DiHA render the most natural viscoelastic properties to the vocal folds. These substances seem to be appropriate for preserving or restoring the vibratory capacity of the vocal folds when glottal insufficiency is treated with augmentative injections.

Update on new biomaterials and their use in reconstructive surgery

Craniofacial reconstruction may be limited by the paucity of autologous materials available and donor site morbidity. Recent advances in the development of biomaterials have given the reconstructive surgeon new options for restoring form and function. There are now biomaterials (second generation) that can elicit a controlled action and reaction to the surrounding tissue environment (bioactive), and those that can exhibit a controlled chemical breakdown and resorption, with ultimate replacement by regenerating tissue (resorbable). Third-generation biomaterials are being designed to stimulate regeneration of living tissues using tissue engineering and in situ tissue regeneration methods. These techniques will lead to limitless possibilities for tissue regeneration and repair. At present, biomaterials that may find future use in craniofacial reconstruction include newly developed bone and skin substitutes and soft-tissue fillers.

Advances in the management of glottic insufficiency

PURPOSE OF REVIEW

Glottic insufficiency secondary to vocal fold scarring, atrophy, or paresis remains a clinically challenging problem for the laryngologist. Numerous methods have been described in the treatment of glottic insufficiency, belying the complexity of the problem. Type I thyroplasty and injection of fat, fascia, and gelatin powder have been the mainstay of treatment to date, but the ability to restore a normal mucosal waveform to a damaged vocal fold remains an elusive goal.

RECENT FINDINGS

Advances in the material and biomedical sciences have allowed the introduction of newer substances and techniques not only to medialize the vocal fold but also to help restore its viscoelastic properties as well. These substances include expanded polytetrafluoroethylene (ePTFE), collagen, cross-linked hyaluronic acid, micronized acellular human dermis calcium hydroxyapatite, and polydimethylsiloxane. ePTFE can be introduced through a window in the thyroid ala or placed intracordally, and the others can be injected either transorally or transcutaneously, allowing in-office placement under simple topical anesthesia.

SUMMARY

Although the ideal augmentation material and technique have yet to be devised, the laryngologist now has several options with which to address the problem of glottic insuffiency. Since the problem is complex and since it is possible that a customized solution may need to be devised on an individual basis, future laryngologists will need to be comfortable with the indications and applications that each material and technique will afford.

Viscoelastic properties of rabbit vocal folds after augmentation

BACKGROUND

Vocal fold function is closely related to tissue viscoelasticity. Augmentation substances may alter the viscoelastic properties of vocal fold tissues and hence their vibratory capacity.

OBJECTIVES

We sought to investigate the viscoelastic properties of rabbit vocal folds in vitro after injections of various augmentation substances.

STUDY DESIGN AND SETTING

Polytetrafluoroethylene (Teflon), cross-linked collagen (Zyplast), and cross-linked hyaluronan, hylan b gel (Hylaform) were injected into the lamina propria and the thyroarytenoid muscle of rabbit vocal folds. Dynamic viscosity of the injected vocal fold as a function of frequency was measured with a Bohlin parallel-plate rheometer during small-amplitude oscillation.

RESULTS

All injected vocal folds showed a decreasing dynamic viscosity with increasing frequency. Vocal fold samples injected with hylan b gel showed the lowest dynamic viscosity, quite close to noninjected control samples. Vocal folds injected with polytetrafluoroethylene showed the highest dynamic viscosity followed by the collagen samples.

CONCLUSIONS

The data indicated that hylan b gel in short-term renders the most natural viscoelastic properties to the vocal fold among the substances tested. This is of importance to restore/preserve the vibratory capacity of the vocal folds when glottal insufficiency is treated with injections.