Functional Analysis of Injectable Substance Treatment on Surgically Injured Rabbit Vocal Folds.

The larynges were studied outside the body, so the tissue was degenerating and the researchers had to create the tension and closure of the vocal folds artificially rather than letting the animal use its own muscles. The injury model was never validated: the researchers did not examine the tissue under a microscope to confirm that their modified incision actually produced a scar, and rabbit vocal folds are known to recover from simpler microflap injuries within 3 to 7 days. Three larynges per group is very small, each larynx varies in anatomy, and the tension applied had to be adjusted by hand for each sample, so the standard deviations were large and the authors themselves say the study shows trends to be tested in a larger study rather than conclusions. Each animal received only one injection, so nothing can be said about repeated or later dosing. The researchers could not reliably check whether the three raters agreed with each other because there were too few samples. The rating form was adapted from a scale validated in human patients and was not itself validated for rabbit larynges, and a new stiffness item was added that has not been tested elsewhere. The laryngeal injury is described in one place as being made in the left vocal fold and elsewhere as the right side being the injured one, so the side of injury is not consistently reported.

Do not read this as evidence that injecting dexamethasone or hyaluronic acid/gelatin helps patients with vocal fold scarring. The work was done on 12 excised rabbit larynges, three per group, the blinded expert ratings found no significant difference between any treatment and saline, and the researchers did not check the tissue under a microscope to confirm that their injury had produced a scar.