Characterization of vocal fold scarring in a canine model

Objective: The objective was to assess the histological and viscoelastic shear tissue properties of the scarred vocal fold lamina propria at 2 and 6 months postoperatively in a canine model. Study Design: Experimental, nonrandomized prospective study. Methods: Six canine larynges were injured using a vocal fold stripping procedure. At 2 and 6 months postoperatively, histological analyses of the scarred and control lamina propria samples were completed for collagen, procollagen, elastin, and hyaluronic acid. Results: In canines killed at 2 months, scarred tissue samples contained increased procollagen and decreased elastin. Elastin fibers in the scarred lamina propria were characteristically tangled and disorganized. In canines killed at 6 months, scarred tissue samples showed decreased elastin and increased collagen. Collagen fibers formed thick, disorganized bundles, and elastin fibers were disorganized throughout the entire scarred vocal fold lamina propria. Viscoelastic shear tissue measurements revealed increased stiffness and viscosity in one of three cases at 2 months and in all three cases at 6 months, indicating increased stiffness and resistance to shear flow during oscillatory shear deformation for scarred tissue samples. No differences were observed between the two postoperative times. Conclusions: Results indicated that viscoelastic tissue changes may take place before scar maturation in the scarred vocal fold lamina propria and that, although abundant collagen deposition may influence viscoelastic shear tissue properties, disorganization of collagen and elastin fibers, thick bundle collagen formation, or the interplay of several of these factors might also play a contributing role.