Augmentation and vocal fold biomechanics in a recurrent laryngeal nerve injury model

Abstract

Objectives/hypothesis Composite vocal fold (VF) biomechanical data are lacking for augmentation after recurrent laryngeal nerve (RLN) injury. We hypothesize resulting atrophy decreases VF stiffness and augmentation restores native VF biomechanics. Methods Sixteen Yorkshire Crossbreed swine underwent left RLN transection and were observed or underwent carboxymethylcellulose (CMC) or calcium hydroxyapatite (CaHa) augmentation at 2 weeks. Biomechanical measurements (structural stiffness, displacement, and maximum load) were measured at 4 or 12 weeks. Thyroarytenoid (TA) muscle cross‐sectional area was quantified and compared with two‐way ANOVA with Tukey's post hoc test. Results After 4 weeks, right greater than left structural stiffness (mean ± SE) was observed (49.6 ± 0.003 vs. 28.4 ± 0.002 mN/mm), left greater than right displacement at 6.3 mN (0.54 ± 0.01 vs. 0.46 ± 0.01 mm, p < .01) was identified, and right greater than left maximum load (72.3 ± 0.005 vs. 40.8 ± 0.003 mN) was recorded. TA muscle atrophy in the injured group without augmentations was significant compared to the noninjured side, and muscle atrophy was seen at overall muscle area and individual muscle bundles. CMC augmentation appears to maintain TA muscle structure in the first 4 weeks with atrophy present at 12 weeks. Conclusions VF biomechanical properties match TA muscle atrophy in this model, and both CMC and CaHa injection demonstrated improved biomechanical properties and slower TA atrophy compared to the uninjured side. Taken together, these data provide a quantifiable biomechanical basis for early injection laryngoplasty to improve dysphonia and potentially improve healing in reversible unilateral vocal fold atrophy. Level of evidence N/A

Office-Based Structural Autologous Fat Injection Laryngoplasty for Unilateral Vocal Fold Paralysis

“…Early injection laryngoplasty with long-lasting fillers [ 47 ] has recently been recommended by scholars for this group of patients. While proper human studies are difficult to design, a recent animal study [ 48 ] performed using recurrent laryngeal nerve resection swine also demonstrated that early injection with calcium hydroxyapatite may improve biomechanical properties and slow thyroarytenoid muscle atrophy compared to the uninjured vocal fold, which is comparable to our protocol and results.…”

Effect of continuous local dexamethasone on tissue biomechanics and histology after inhalational burn in a preclinical model

“…Euthanasia was performed after general anesthesia induction with intravenous pentobarbital (100 mg/kg) and confirmed via vital sign monitoring according to institutional protocol. The larynx was extracted immediately after euthanasia and sectioned in the sagittal plane, with care taken to preserve the anterior commissure 24–26 . Specimens were then frozen at −80°C until biomechanical and subsequent histologic analysis.…”

“…Each specimen was positioned beneath a camera to align a template with predetermined indentation points along the entire glottis and subglottis (Figure 2A). Normal indentation was conducted using a Biomomentum Mach‐1 v500css (Laval, Quebec, Canada) with a 1.5 N uniaxial load call as previously established 26,27 . For our evaluation, a 2 mm spherical indenter tip with a velocity of 1.2 mm/s and indentation depth of 0.3 mm was used.…”

“…Normal indentation was conducted using a Biomomentum Mach-1 v500css (Laval, Quebec, Canada) with a 1.5 N uniaxial load call as previously established. 26,27 For our evaluation, a with a discrepant assessment of more than one point were rereviewed by both pathologists in order to achieve consensus. Epithelial ulceration and fibrosis were graded on a five-point scale based on the percentage of ulcerated surface epithelium and fibrotic submucosa inferior to the vocalis muscle, respectively (0: 0%, 1: 1%-25%, 2: 25%-50%, 3: 50%-75%, 4: 75%-100%).…”

Changes in vocal fold gene expression and histology after injection augmentation in a recurrent laryngeal nerve injury model

“…Recent work evaluating the effect of injection augmentation on vocal fold stiffness in an RLN injury model demonstrated biomechanical changes in the injected fold and compensatory changes in the healthy contralateral side. 14 While the thyroarytenoid area was significantly decreased after RLN transection and unaffected by injection augmentation, vocal fold stiffness on the injected side was closer to native tissue properties than the untreated denervated vocal fold. Perhaps more interesting, however, was that healthy vocal folds contralateral to an injected vocal fold also showed increased stiffness, suggestive of compensatory changes separate from the biomechanical properties of the injectate itself.…”