Viscoelasticity in scarred rabbit vocal folds after hyaluronan injection

Abstract

Problem: Hyaluronan has been shown to improve the viscoelastic properties after injections in normal rabbit vocal folds and in patients with unilateral paresis and vocal fold atrophy. Viscoelasticity is important to the vocal fold vibratory capacity. The aim of the study was to analyze the short-term viscoelastic properties after the injection of hyaluronan in scarred rabbit vocal folds. Methods: Vocal folds of New Zealand rabbits were scarred and after 2 months one group received injections with crosslinked hyaluronan and another group was injected with saline. After 2 more months (4 months after scarring) both groups and a third group of control animals with normal vocal folds were euthanized. The larynges were dissected out, 16 vocal folds were frozen in -20 C for viscoelastic measurements, whereas 16 vocal folds were prepared and stained for histological analysis including measurements from digitized slides. Two methods were used for the viscoelastic analysis: (1) analyses were made on intact vocal folds with a linear skin rheometer (LSR) adapted to laryngeal measurements, and (2) the vocal folds were dissected and analyzed in a parallel-plate rheometer. Results: Measurements on the digitized slides showed a thickened lamina propria of the scarred samples as compared to the normal vocal folds ( P < 0.05). The viscoelastic LSR analysis on intact vocal folds showed a tendency to stiffening of the scarred vocal folds as compared to the normal group ( P = 0.05). The parallel plate rheometry on the same samples after dissection showed a decreased dynamic viscocity of the scarred samples injected with hyaluronan (Hylaform) as compared to the normals and to the scarred group that received no hyaluronan ( P < 0.01 and P < 0.05, respectively). Conclusion: Injection of scarred rabbit vocal folds with hyaluronan in the short term rendered improved viscoelastic parameters. Significance: Hyaluroan may prove useful for treating vocal fold scarring. Support: None reported.