Abstract
To derive optimal thyroid cartilage window for medialisation thyroplasty in Indian population and comparision of the same with standard parameters including Isshiki’s thyroplasty type I. Along with comparision it is also attempted to bring out difference if any, to provide a better guidelines of medialisation thyroplasty in Indian population. A total No of 52 (35 male and 17 female) cadaveric laryngeal samples (formalin fixed) taken into study. Cartilage window over thyroid lamina is created and increased gradually. Endoscopic examination of medialisation by appropriate silastic block of true vocal cord noted at each level. Relevant thyroid anatomy at window corners also taken into consideration. In Indian set up, dimensions of window required for medialisation thyroplasty are slightly lesser than the average size quoted by premier study of Isshiki when compared in male population. The window size of males which produced ideal medialisation was 12–14 mm in length and 5 mm in height. In females it was 10–11 mm in length and 4 mm in height.
Keywords: Medialisation thyroplasty Indian, Thyroid cartilage window dimension, Isshiki type I thyroplasty
Introduction
The vocal fold is a forbidden place; we are not allowed to enter deep inside. All we can safely do is exert influence from outside. Isshiki
Speech is one of the most complex and highly skilled, learned behaviour that humans possess. Production of speech requires controlled integration of respiratory, phonatory and articulatory musculature. The role of the larynx in voice production is to efficiently convert aerodynamic energy of the chest and lungs into acoustic energy. Critical in this process is vocal fold adduction, which potentiates glottal valve closure. Glottic insufficiency causes hoarseness. Vocal fold paralysis is a common cause of hoarseness in otolaryngeal practice. The vocal fold is composed of several distinct layers or compartments, and the proper diagnosis and treatment of glottic insufficiency relies on correctly determining the level of the problem It is important to preserve the relationship of the five layers of the vocal fold for the production of the mucosal wave and normal voice [1, 2]. Diagnosis of glottic insufficiency relies primarily on laryngoscopic examination [3]. A thorough knowledge of relevant surgical anatomy is a must for any surgeon before contemplating any laryngeal surgical procedures. Precise knowledge of the level of the true vocal cord as projected on the external thyroid cartilage is of critical importance for the laryngeal surgeon. During thyroplasty type I, a window is made in the thyroid cartilage lateral to the true vocal cord in order to mobilize the paralyzed cord medially. Misplacement of the window superiorly even by a few millimetres will result in medialisation of the ventricle and not the true vocal cord. This will result in clinical failure of the surgical objective to improve phonatory quality [4]. Understanding the morphology of the thyroid cartilage is absolutely necessary before contemplating the intricate laryngeal framework surgeries where in precision and exact measurements are essential for optimum results. Modifications of Isshiki original medialisation technique include changes in the size and placement of the window and various techniques for stabilization of the implant. Most of the relevant anatomic details for LFS are based on western population and the studies pertaining to Indian population are extremely scarce. We propose to undertake this study in order to understand the relevant anatomy of the thyroid cartilage in our north Indian population, its application in medialisation thyroplasty. In our study, we will test the traditional window i.e. the window created in Isshiki type I thyroplasty, with an attempt to to identify an appropriate site and size of the window in Indian population so as to get optimal medialisation. The results will be confirmed by visualizing the endolarynx with a zero degree and thirty-degree endoscope on cadaveric larynx.
Aim
To understand the normal anatomy of the thyroid cartilage in North Indian population in order to assess the optimal dimensions and site of cartilage window to be formed in Indian patients undergoing the surgical procedure of medialisation thyroplasty.
Objectives
To derive optimal thyroid cartilage window for medialisation thyroplasty in Indian population and comparision of the same with standard parameters including Isshiki’s thyroplasty type I.
Along with comparision it is also attempted to bring out difference if any, to provide a better guidelines of medialisation thyroplasty in Indian population.
Method
The data for the present study was collected from the cadaveric larynges from the department of Anatomy, of a medical college attached to a tertiary care hospital of the Indian Armed Forces in North India (Table 1).
Table 1.
Thickness measured at the corners of thyroid window as per standardized Isshiki type I thyroplasty procedure
| Index | Male | Female | ||
|---|---|---|---|---|
| Mean in mm | Range in mm | Mean in mm | Range in mm | |
| Anterio-superior left | 2.3 ± 0.2 | 1.6–2.6 | 1.7 ± 0.4 | 1.2–2.4 |
| Anterio-superior right | 2.4 ± 0.2 | 1.6–2.7 | 1.7 ± 0.4 | 1.2–2.4 |
| Anterio-inferior left | 3.1 ± 0.3 | 2.4–3.5 | 2.2 ± 0.4 | 1.8–3.1 |
| Anterio-inferior right | 3.2 ± 0.2 | 2.5–3.6 | 2.2 ± 0.4 | 1.8–3.2 |
| Posterio-superior left | 3.3 ± 0.3 | 2.5–3.7 | 2.5 ± 0.3 | 2.2–3.3 |
| Posterio-superior right | 3.4 ± 0.3 | 2.6–3.8 | 2.5 ± 0.3 | 2.1–3.4 |
| Postrio-inferior left | 3.5 ± 0.5 | 2.9–4.3 | 3.1 ± 0.5 | 2.4–3.8 |
| Posterio-inferior right | 3.7 ± 0.3 | 2.8–4.3 | 3 ± 0.5 | 2.4–3.8 |
Sample size
Sample size was calculated keeping in view at the most 5% risk, with minimum 80% power and 5% significance level (significant at 95% confidence level.
Methods
- Study design
Cross sectional study
- Time line
24 months
- Place of study
Tertiary Care Hospital of Armed Forces.
- Sample size
52
Inclusion criteria
Cadaveric adult larynx specimens of both the sexes will be collected.
Exclusion criteria
Post-mortem larynx specimens of hanging, strangulation, lacerated wound over the neck will be excluded.
Post-mortem larynx specimens with history of any previous laryngeal surgery will be excluded.
Methodology
52 cadaveric larynx specimens (35 male and 17 female) were collected and fixed in 10% formalin solution. After fixation careful dissection was done to isolate thyroid cartilages. All measurements were taken with the help of vernier calliper goniometer and protractor.
Thyroid cartilage thickness was measured up to the nearest 0.1mm with a vernier calliper. The length and width of each window and thyroid cartilage height in the midline (distance from the lower border of the thyroid cartilage to the thyroid notch) was measured to the nearest 0.5mm.
To start with 10 × 4 mm window was created initially; the upper border of which was at the level of midpoint superior and inferior notch, the anterior end 5 mm posterior to the line joining superior and inferior notch. After the removal of the thyroid cartilage from window, silastic block was inserted and checked endoscopically.
This was followed by enlarging the window to 11 × 4 mm, 11 × 5 mm, 12 × 5 mm, 12 × 6 mm, 13 × 6 mm and finally 14 × 6 mm. This procedure was done in all larynges. Endoscopic visualisation was done to look for medialisation.
Observations
Our study provides a comprehensive and detailed description of the dimensions of the thyroid cartilages window in adult human larynx cadavers of Indian origin. All the major measurements of thyroid cartilage were found to be more in males as compared to females except for thyroid angle. Various dimensions of thyroid cartilages are smaller as compared to the African and Western population. At the vocal cord level, the cartilage also becomes thicker posteriorly, in both men and women.
It was observed that in males the ideal size of the window which produced ideal medialisation was 12–14 mm in length and 5 mm in height. In females it was 10–11 mm in length and 4 mm in height.
Sizes smaller to the above size in length caused less medialisation of the vocal cord specially posterior part of vocal cord was not getting medialised adequately. Sizes larger than the above size was not suitable as the silastic was abutting the crico-arytenoid joint and cartilage posteriorly.
Sizes larger in height caused fracture of inferior border of thyroid cartilage during manipulation; it also caused a bulge of false vocal cord superiorly.
Results
In the present study a total no of 52 thyroid cartilages were studied, out of which 35 thyroid cartilages were of male and 17 of female. Results of measurement at the corners of thyroid window is tabulated in terms of mean and range in specimen of both sexes:
In Indian set up, dimensions of window required for medialisation thyroplasty are slightly lesser than the average values mentioned in premier study of Isshiki, as far as the breadth of cartilage window is concerned in male population.
Data reporting
Means and proportions were calculated for continuous and categorical variables respectively. Tests for normality were done before hand and Difference between means was compared using independent sample t test. A P value < 0.05 was considered statistically significant. Data entry was done in MS Excel 2013 and SPSS Version 21.0 was used for statistical analysis
Discussion
When compared between the two sexes, dimension values of cartilage window are observed to be more in males compared to females, and the difference was statistically significant. This study when compared with the study done by Nobuhiko Isshiki (1989), we got slightly lesser values of dimension of window for medialisation window than the premier study of Isshiki. It holds truer for the breadth of cartilage window in male Indian population.
As per Isshiki “The window should be 4–6 mm high and 8–14 mm wide, and should always be large for a large thyroid ala. On average, the windows are 6 × 12 mm in men and 4 × 10 mm in women”. So values observed in this study over indoian population fall within the range though on the lower side when compared to Isshiki study [5].
When compared to Maragos study [6] where he standardised the length of the Type I window at 10.0 and 14.0 mm for females and males, respectively, In this study our dimension in terms of length of window in male population found to be on lower side.
In this study the measurements of dimension for the optimal window size in Type I thyroplasty collaborates and fall within range provided by those of Koufman [7] who used a different set of formulas and measurements of the thyroid cartilage height and width.
In our study it was observed that in males the size of the window which produced ideal medialisation was 12–14 mm in length and 5 mm in height. In females it was 10–11 mm in length and 4 mm in height. These findings of thyroplasty type I window were similar to other previously done studies [5, 6, 8–10].
Key message
Our study has provided data about North Indian population which can be confidently used in planning medialisation thyroplasty.
The window size of males which produced ideal medialisation was 12–14 mm in length and 5 mm in height. In females it was 10–11 mm in length and 4 mm in height which is consistent with Isshiki’s technique.
Limitation
This study was carried out in cadaver which were preserved in formalin. It is known that tissue tend to shrink in size due to fixation and preservation of cadaver. Therefore, there may be some difference/ variation in the measurements obtained in this study and the actual life situations.
Funding
The authors have no relevant financial or non financial interest to disclose.
Declarations
Conflict of interest
The authors have no conflicts of interest to declare that are relevant to the content of this article.
Human participants and /or animals
Study done on human cadaveric laryngeal specimens.
Informed consent/ Ethical approval
Institutional ethical approval vide: Ethical Committee No 109/12/Dec/BH-2016dt 27 Dec 2016.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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