An ex vivo model to evaluate the effect of cyclical adductory forces on maintenance of arytenoid abduction after prosthetic laryngoplasty performed with and without mechanical arytenoid abduction.

The researchers developed a model to investigate the effect of repetitive adduction forces, similar to those experienced during swallowing or coughing, on an area in the throat known as the arytenoid cartilage. The study found that such forces led to significant loss of abduction, a movement away from the midline, and that the use of a clamp during a surgical procedure known as laryngoplasty did not reduce this effect.

Developing a Model

• The researchers created a model to simulate the effect of cyclical adduction forces on the left arytenoid cartilage. Adduction forces are those that draw a part of the body toward the midline, and in this context, they mimic the forces generated during activities such as swallowing or coughing.

Experiment Setup

• For the experiment, the researchers used 14 cadaveric equine larynges. They performed left laryngoplasty, a surgical procedure to adjust the positioning of the cartilage, on each larynx using a single suture of #5 Ethibond. In half of the cases, the arytenoid was abducted with a clamp before the knot was tied, while in the other half this step was omitted.
• Each laryngoplasty was then subjected to forces ranging from 2 to 26 Newtons at a frequency of 0.5 Hertz for 5000 cycles within a servohydraulic test frame. This mimicked the effect of repetitive adduction forces that would occur in a living subject.
• The researchers documented the displacement of the arytenoid cartilage at 1 Hertz intervals and compared the median percent loss of abduction between the two groups.

Results

• The median left arytenoid abduction distance achieved was 16.9 millimeters, with a range of 9.8 to 19.8 millimeters.
• One larynx in each group failed before completing 1000 cycles. Their failures were determined by progressive displacement of the testing actuator and confirmed by measurement.
• There was no difference in the loss of abduction, or movement away from the midline, between the larynges that were clamped and those that were not after 5000 cycles.
• The model of cyclical adduction generated arytenoid displacements similar to those observed in the first week following surgery in actual patients.

Conclusions

• The study revealed that ex vivo cyclical adductory forces produced a significant loss of laryngoplasty abduction, impacting the effectiveness of the procedure.
• The use of a clamp to abduct the arytenoid cartilage before knot tying during the surgery did not reduce this loss of abduction. This challenges the common surgical practice and suggests that other methods may need to be explored to maintain arytenoid abduction following laryngoplasty.