Three-dimensional biomechanics of simulated laryngeal abduction in horses.

The research aims to understand the effect of simulated contraction of a certain muscle (cricoarytenoideus dorsalis or CAD) on the movement of arytenoid cartilage in the larynx of horses. Using a range of techniques, it was found that the rocking motion, prompted by the lateral belly of CAD muscle, was crucial for arytenoid cartilage abduction.

Methods and Techniques Used

• The researchers used larynxes from five equine cadavers for the study. These animal models were used to simulate the workings of a live horse’s larynx without the subjectivity associated with a live specimen.
• Serial computed tomographic scans of each larynx were conducted at seven different forces. These forces simulated contraction of medial, lateral, and combined bellies of the left CAD muscle. The use of this technology allowed the researchers to gain detailed 3D images of the cartilage and understand the impact of different forces and angles.
• Three-dimensional reconstruction of radiopaque markers placed at anatomic landmarks on the left arytenoid and cricoid cartilages enabled the researchers to quantify marker displacement in relation to a Cartesian coordinate system. This gave accurate measurements of displacement and was key in assessing the effectiveness of contraction simulation.
• Rotation (roll, pitch, and yaw) of the dorsal and ventral arytenoid planes was calculated relative to a plane formed by the coordinates of three markers on the cricoid cartilage by using Euler angles.

Findings

• Data from displacement and rotation showed that a rocking motion occurs in arytenoid abduction. They found the rotational component mainly attributed to pitch; greater pitch was associated with the action of the lateral belly of the CAD muscle.
• Roll of the ventral arytenoid plane was mainly associated with the action of the medial belly, counteracting the arytenoid cartilage’s inclination to rotate medially into the rima glottidis lumen.
• The markers on the arytenoid cartilage weren’t maintained at a constant distance during the contraction, implying that the arytenoid cartilage underwent slight deformation and was not rigid during the abduction process.

Conclusions

• The researchers concluded that the abduction of arytenoid cartilage relies on the rocking motion brought about by the lateral belly of the CAD muscle.
• The results suggest that surgical procedures, such as laryngoplasty suture placement, should aim to mimic the action of the CAD muscle’s lateral, rather than medial, belly.