Quantification of injection force mechanics during injection laryngoplasty.

Objectives: In-office or operative injection laryngoplasty requires needle stability for accurate material placement. To date, no reports compare injection forces based on needle gauge, bends, length, or material type or temperature. We hypothesize these factors alter injection forces and could impact clinical use.
Methods: Swine larynges were placed in a compression testing machine. Syringes were affixed to a stabilizing crossbeam. Straight needles (25G 1.5-inch; 27G 1.25-inch; or 9.8-inch malleable shaft 16G per oral with 24G tapered needle tip) were inserted into the swine vocal folds to simulate realistic tissue resistance pressure. Compressive loading was conducted at 40 mm/minute until steady-state force was achieved. Tests were completed with calcium hydroxylapatite (CaHa), carboxymethylcellulose, and hyaluronic acid at various temperatures and CaHa with various bends in the needles (n = 3 per group, comparisons performed by two-way analysis of variance (ANOVA), Tukey's post-hoc).
Results: Needle size, shape, and temperature altered injection force. Steady-state force was highest with the per-oral needle at a mean of 44.55N compared to 26.44N and 29.77N in the 25G and 27G percutaneous needles, respectively (P < 0.001). Stiffness rate (initial increasing force vs. distance to initiate injection) ranged from 19.75N/mm (per oral) to 22.06N/mm (25G) to 24.56N/mm (27G), (P = 0.875). Adding multiple bends to the per-oral needle increased stiffness rate to 24.99N/mm (P = 0.035), whereas the 25G needle stiffness rate remained unchanged (P = 0.941), with the stiffness rate decreasing in the 27G needle with increasing bends (P = 0.033). Increased temperature decreased injection forces across all materials.
Conclusion: Needle caliber, length, and bends impact steady-state forces and stiffness rates during vocal fold injection.
Level of Evidence: NA Laryngoscope, 129:1060-1066, 2019.
(Published 2018. This article is a U.S. Government work and is in the public domain in the USA.)